4 energy expenditure and fatigue chapter. learning objectives learn how exercise affects metabolism...
TRANSCRIPT
4
Energy Expenditure and Fatigue
chapter
Learning Objectives
bull Learn how exercise affects metabolism and how metabolism can be monitored to determine energy expenditure
bull Discover the underlying causes and sites of fatigue in muscles
Respiratory Exchange Ratio
bull The ratio between CO2 released (VCO2) and oxygen consumed (VO2)
bull RER = VCO2 VO2
bull The RER value at rest is usually 078 to 080
RER Determining Substrate Utilization
Carbohydrate
6 O2 + C6H12O6 rarr 6 CO2 + 6 H2O + 38 ATP
RER = VCO2 VO2 = 6 CO2 6 O2 = 10
Fat
C16H32O2 + 23 O2 rarr 16 CO2 + 16 H2O + 129 ATP
RER = VCO2 VO2 = 16 CO2 23 O2 = 070
Resting Metabolic Rate (RMR)
RMR is the minimum amount of energy required bythe body to sustain basic cellular function
ndash Fat-free massndash Body surface areandash Ranges from 1100 to 2500 kcaldayndash When activity is added daily caloric expenditure is
1700 to 3100 kcalday
Factors That Affect RMR
bull Age RMR gradually decreases with age generally because of a decrease in fat-free mass
bull Body temperature RMR increases with increasing temperature
bull Psychological stress Stress increases activity of the sympathetic nervous system
bull Hormones Thyroxine from the thyroid gland and epinephrine from the adrenal medulla both increase RMR
Metabolic Rate During Submaximal Exercise
bull Metabolism increases in direct proportion to the increase in exercise intensity
bull During exercise at a constant power output (work rate) VO2 increases from its resting value to a steady-state value within 1-2 minutes
bull There is a linear increase in the VO2 with increases in power output (work rate)
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Learning Objectives
bull Learn how exercise affects metabolism and how metabolism can be monitored to determine energy expenditure
bull Discover the underlying causes and sites of fatigue in muscles
Respiratory Exchange Ratio
bull The ratio between CO2 released (VCO2) and oxygen consumed (VO2)
bull RER = VCO2 VO2
bull The RER value at rest is usually 078 to 080
RER Determining Substrate Utilization
Carbohydrate
6 O2 + C6H12O6 rarr 6 CO2 + 6 H2O + 38 ATP
RER = VCO2 VO2 = 6 CO2 6 O2 = 10
Fat
C16H32O2 + 23 O2 rarr 16 CO2 + 16 H2O + 129 ATP
RER = VCO2 VO2 = 16 CO2 23 O2 = 070
Resting Metabolic Rate (RMR)
RMR is the minimum amount of energy required bythe body to sustain basic cellular function
ndash Fat-free massndash Body surface areandash Ranges from 1100 to 2500 kcaldayndash When activity is added daily caloric expenditure is
1700 to 3100 kcalday
Factors That Affect RMR
bull Age RMR gradually decreases with age generally because of a decrease in fat-free mass
bull Body temperature RMR increases with increasing temperature
bull Psychological stress Stress increases activity of the sympathetic nervous system
bull Hormones Thyroxine from the thyroid gland and epinephrine from the adrenal medulla both increase RMR
Metabolic Rate During Submaximal Exercise
bull Metabolism increases in direct proportion to the increase in exercise intensity
bull During exercise at a constant power output (work rate) VO2 increases from its resting value to a steady-state value within 1-2 minutes
bull There is a linear increase in the VO2 with increases in power output (work rate)
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Respiratory Exchange Ratio
bull The ratio between CO2 released (VCO2) and oxygen consumed (VO2)
bull RER = VCO2 VO2
bull The RER value at rest is usually 078 to 080
RER Determining Substrate Utilization
Carbohydrate
6 O2 + C6H12O6 rarr 6 CO2 + 6 H2O + 38 ATP
RER = VCO2 VO2 = 6 CO2 6 O2 = 10
Fat
C16H32O2 + 23 O2 rarr 16 CO2 + 16 H2O + 129 ATP
RER = VCO2 VO2 = 16 CO2 23 O2 = 070
Resting Metabolic Rate (RMR)
RMR is the minimum amount of energy required bythe body to sustain basic cellular function
ndash Fat-free massndash Body surface areandash Ranges from 1100 to 2500 kcaldayndash When activity is added daily caloric expenditure is
1700 to 3100 kcalday
Factors That Affect RMR
bull Age RMR gradually decreases with age generally because of a decrease in fat-free mass
bull Body temperature RMR increases with increasing temperature
bull Psychological stress Stress increases activity of the sympathetic nervous system
bull Hormones Thyroxine from the thyroid gland and epinephrine from the adrenal medulla both increase RMR
Metabolic Rate During Submaximal Exercise
bull Metabolism increases in direct proportion to the increase in exercise intensity
bull During exercise at a constant power output (work rate) VO2 increases from its resting value to a steady-state value within 1-2 minutes
bull There is a linear increase in the VO2 with increases in power output (work rate)
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
RER Determining Substrate Utilization
Carbohydrate
6 O2 + C6H12O6 rarr 6 CO2 + 6 H2O + 38 ATP
RER = VCO2 VO2 = 6 CO2 6 O2 = 10
Fat
C16H32O2 + 23 O2 rarr 16 CO2 + 16 H2O + 129 ATP
RER = VCO2 VO2 = 16 CO2 23 O2 = 070
Resting Metabolic Rate (RMR)
RMR is the minimum amount of energy required bythe body to sustain basic cellular function
ndash Fat-free massndash Body surface areandash Ranges from 1100 to 2500 kcaldayndash When activity is added daily caloric expenditure is
1700 to 3100 kcalday
Factors That Affect RMR
bull Age RMR gradually decreases with age generally because of a decrease in fat-free mass
bull Body temperature RMR increases with increasing temperature
bull Psychological stress Stress increases activity of the sympathetic nervous system
bull Hormones Thyroxine from the thyroid gland and epinephrine from the adrenal medulla both increase RMR
Metabolic Rate During Submaximal Exercise
bull Metabolism increases in direct proportion to the increase in exercise intensity
bull During exercise at a constant power output (work rate) VO2 increases from its resting value to a steady-state value within 1-2 minutes
bull There is a linear increase in the VO2 with increases in power output (work rate)
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Resting Metabolic Rate (RMR)
RMR is the minimum amount of energy required bythe body to sustain basic cellular function
ndash Fat-free massndash Body surface areandash Ranges from 1100 to 2500 kcaldayndash When activity is added daily caloric expenditure is
1700 to 3100 kcalday
Factors That Affect RMR
bull Age RMR gradually decreases with age generally because of a decrease in fat-free mass
bull Body temperature RMR increases with increasing temperature
bull Psychological stress Stress increases activity of the sympathetic nervous system
bull Hormones Thyroxine from the thyroid gland and epinephrine from the adrenal medulla both increase RMR
Metabolic Rate During Submaximal Exercise
bull Metabolism increases in direct proportion to the increase in exercise intensity
bull During exercise at a constant power output (work rate) VO2 increases from its resting value to a steady-state value within 1-2 minutes
bull There is a linear increase in the VO2 with increases in power output (work rate)
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Factors That Affect RMR
bull Age RMR gradually decreases with age generally because of a decrease in fat-free mass
bull Body temperature RMR increases with increasing temperature
bull Psychological stress Stress increases activity of the sympathetic nervous system
bull Hormones Thyroxine from the thyroid gland and epinephrine from the adrenal medulla both increase RMR
Metabolic Rate During Submaximal Exercise
bull Metabolism increases in direct proportion to the increase in exercise intensity
bull During exercise at a constant power output (work rate) VO2 increases from its resting value to a steady-state value within 1-2 minutes
bull There is a linear increase in the VO2 with increases in power output (work rate)
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Metabolic Rate During Submaximal Exercise
bull Metabolism increases in direct proportion to the increase in exercise intensity
bull During exercise at a constant power output (work rate) VO2 increases from its resting value to a steady-state value within 1-2 minutes
bull There is a linear increase in the VO2 with increases in power output (work rate)
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Increase in Oxygen Uptake with Increasing Power Output
Reprinted by permission from GA Gaesser and DC Poole 1996 ldquoThe slow component of oxygen uptake kinetics in humansrdquo Exercise and Sport Sciences Reviews 24 36
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Maximal Oxygen Uptake
bull VO2max The maximal capacity for oxygen consumption by the body during maximal exertion
bull Single best measurement of cardiorespiratory endurance and aerobic fitness (800 or 1600m)
bull Increases with physical trainingbull Generally expressed relative to body weight
(ml kg-1 min-1)bull Normally active untrained college-aged students =
38-42 ml kg-1 min-1
bull VO2max declines in active people after age 25-30 by ~ 1 per year
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Relationship Between Exercise Intensity and Oxygen Uptake in Trained and
Untrained Man
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Estimating Anaerobic Effort
bull Oxygen deficit 氧債 is calculated as the difference between the oxygen required for a given exercise intensity and the actual oxygen consumption
bull Anaerobic effort can be estimated by examining excess postexercise oxygen consumption (EPOC)mdashthe mismatch between O2 consumption and energy requirements
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Oxygen Requirement During Exercise and Recovery
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Factors Responsible for EPOC
bull Rebuilding depleted ATP and PCr suppliesbull Clearing lactate produced by anaerobic metabolism
bull Replenishing O2 supplies borrowed from hemoglobin and myoglobin
bull Removing CO2 that has accumulated in body tissues
bull Increased metabolic and respiratory rates due to increased body temperature
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Lactate Threshold
bull It is the point at which blood lactate begins to accumulate substantially above resting concentrations during exercise of increasing intensity
bull The rate at which lactate production exceeds lactate clearance
bull Usually expressed as a percentage of maximal oxygen uptake
bull A high lactate threshold can indicate potential for better endurance performance
bull Lactate accumulation contributes to fatigue
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Relationship Between Exercise Intensity and Blood Lactate Concentration
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Lactate Threshold and Endurance Performance
Lactate threshold (LT) when expressed as a percentage of VO2max is one of the best determinants of an athletersquos pace in endurance events such as running and cycling While untrained people typically have LT around 50 to 60 of their VO2max elite athletes may not reach LT until around 70 to 80 VO2max
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Economy of Effort
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Measuring Energy Use During Exercise
Key Pointsbull Excess postexercise oxygen consumption (EPOC)
is the metabolic rate above resting levels after exercise
bull Lactate threshold is the point at which blood lactate production begins to exceed the bodyrsquos ability to clear or remove lactate
bull Individuals with higher lactate thresholds expressed as a percentage of VO2max are capable of the best endurance performance
bull Aerobic endurance performance capacity is also associated with a high economy of effort
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Fatigue and its Causes
bull Energy delivery (ATP-PCr anaerobic glycolysis and oxidation)
bull Accumulation of metabolic by-products such as lactate and H+
bull Failure of the muscle fiberrsquos contractile mechanismbull Alteration in the nervous system
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Energy Systems and Fatigue
bull PCr depletionbull Glycogen depletion (ldquohitting the wallrdquo)
ndash Pattern of glycogen depletion from Type I and II fibers depends on the duration and intensity of the activity
ndash Glycogen depletion is selective to the muscle groups involved in the activity
ndash Depletion of liver glycogen to increase blood glucose increases muscle glycogen utilization
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Decline in Muscle Glycogen
Adapted by permission from DL Costill 1986 Inside running Basics of sports physiology (Indianapolis Benchmark Press) Copyright 1986 Cooper Publishing Group Carmel IN
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Glycogen Depletion in Different Muscle Fibers
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Glycogen Depletion in Different Muscle Groups
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
High Muscle Temperature Impairs Skeletal Muscle Function and Metabolism
Adapted by permission from SDR Galloway and RJ Maughan 1997 Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man Medicine and Science in Sports and Exercise 29 1240-1249
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Metabolic By-Products and Fatigue
bull Short-duration activities depend on anaerobic glycolysis and produce lactate and H+
bull Cells buffer H+ with bicarbonate (HCO3ndash) to keep cell pH
between 64 (at exhaustion) and 71bull Intercellular PH lower than 69 however slows
glycolysis and ATP productionbull When pH reaches 64 H+ levels inhibit glycolysis and
result in exhaustion
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Changes in Muscle pH During Sprint Exercise and Recovery
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Neuromuscular Fatigue
Fatigue may involve1 Decreased release or synthesis of acetylcholine2 Hyperactive acetylcholinesterase(break down ACH)
3 Hypoactive acetylcholinesterase(accumulate excessive ACH unable relax)
4 Increased threshold for stimulation of the muscle fiber5 Competition with ACh for the receptors on the muscle
membrane6 Potassium may leave the intracellular space
decreasing the membrane potential below resting values( < -70mv)
7 Central nervous system fatigue
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism
Causes of Fatigue
Key Pointsbull Fatigue may result from depletion of PCr or
glycogen which impairs ATP productionbull The H+ generated by lactic acid leads to fatigue by
decreasing muscle pH which impairs the cellular processes of energy production and muscle contraction
bull Failure of neural transmission may cause some fatigue
bull The central nervous system may also limit exercise performance as a protective mechanism