Aerobic & Anaerobic Aerobic & Anaerobic Metabolism in MusclesMetabolism in Muscles

ObjectivesObjectives

Recognize the importance of ATP as Recognize the importance of ATP as energy source in skeletal muscle.energy source in skeletal muscle.

Understand how skeletal muscles Understand how skeletal muscles derive and utilize ATP for energy.derive and utilize ATP for energy.

Differentiate between energy Differentiate between energy metabolism in red and white muscle metabolism in red and white muscle fibers.fibers.

ATP or ATP or adenosine triphosphateadenosine triphosphate is the energy currency used by is the energy currency used by our body everyday to perform a number of tasks:our body everyday to perform a number of tasks:

METABOLISM: METABOLISM: EnergyEnergy ReleaseRelease

Maintain body temperature

• Repair damaged cells

• Digestion of food

• Mechanical work – movement

ATP ↔ ADP + Energy

ATP …….. Contd.ATP …….. Contd. The nucleotide coenzyme The nucleotide coenzyme adenosineadenosine

triphosphate (ATP)triphosphate (ATP) is the most important form of is the most important form of chemical energy stored in cellschemical energy stored in cells

Breakdown of ATP into ADP+POBreakdown of ATP into ADP+PO44 releases energy releases energy

Muscles typically Muscles typically store limitedstore limited amounts of ATP – amounts of ATP – enough to power enough to power 4-6s 4-6s of activityof activity

So resting muscles must have energy stored in So resting muscles must have energy stored in other ways.other ways.

ATP Is GeneratedATP Is GeneratedThrough 3 Energy SystemsThrough 3 Energy Systems1.1. ATP-PCr system ATP-PCr system

2.2. Glycolytic systemGlycolytic system

3.3. Oxidative systemOxidative system

The process that facilitates muscular contraction is entirely dependent on body’s ability to provide & rapidly

replenish ATP

INTERACTION OF ENERGY INTERACTION OF ENERGY SYSTEMSSYSTEMS

Immediate Short-term Long-term

100%%

Cap

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of E

nerg

y Sy

stem

10 sec 30 sec 2 min 5+ min

Energy Transfer Systems and ExerciseEnergy Transfer Systems and Exercise

Aerobic Energy System

Anaerobic Glycolysis

ATP - CP

Exercise Time

Energy Systems Energy Systems for Exercisefor Exercise

Energy SystemsEnergy SystemsMole of Mole of ATP/minATP/min

Time to Time to FatigueFatigue

Immediate:Immediate: ATP - PCr ATP - PCr(ATP & phosphocreatine)(ATP & phosphocreatine)

445 to 10 sec5 to 10 sec

Short Term:Short Term: GlycolyticGlycolytic(Glycogen-Lactic Acid)(Glycogen-Lactic Acid)

2.52.51 to 2 min1 to 2 min

Long Term:Long Term: OxidativeOxidative11Unlimited Unlimited timetime

Energy RequirementsEnergy Requirements

The three energy systems often operate The three energy systems often operate simultaneously during simultaneously during physical activity.physical activity.

Relative contribution of each system to Relative contribution of each system to total energy requirement differs markedly total energy requirement differs markedly depending on exercise depending on exercise intensityintensity & & durationduration..

Magnitude of energy from anaerobic sources Magnitude of energy from anaerobic sources depends on depends on person’s capacity and tolerance person’s capacity and tolerance for lactic acid accumulation for lactic acid accumulation (Athletes are (Athletes are trained so that they will have better tolerance trained so that they will have better tolerance for lactic acid) for lactic acid) ..

As exercise intensity diminishes and duration As exercise intensity diminishes and duration extends extends beyond 4 minutes,beyond 4 minutes, energy more energy more dependent on dependent on aerobic metabolismaerobic metabolism..

Energy MetabolismEnergy Metabolism

AerobicAerobicWith oxygenWith oxygenSource of energy: Source of energy:

mainly mainly fatty fatty acidsacids, then , then carbohydratecarbohydrate

COCO22, H, H22O & ATPO & ATP

AnaerobicAnaerobic– Without oxygenWithout oxygen– Source of Source of

energy: energy: Carbohydrate Carbohydrate (glycolysis)(glycolysis)

– Lactate & ATPLactate & ATP

What factors contribute to What factors contribute to muscle fatigue?muscle fatigue?

Fatigued muscle no longer contracts due Fatigued muscle no longer contracts due to:to: Build up of lactic acid (low pH of Build up of lactic acid (low pH of

sarcoplasm)sarcoplasm)Exhaustion of energy resources (Exhaustion of energy resources (

ADP & ADP & ATP) ATP)Ionic imbalance: muscle cells is Ionic imbalance: muscle cells is

less responsive to motor neuronal less responsive to motor neuronal stimulationstimulation

Muscle FatigueMuscle Fatigue

How would a fatigued muscle be How would a fatigued muscle be able again to contractable again to contract

Recovery period: Begins immediately after activity ends

Oxygen debt (excess post-exercise oxygen consumption)◦Amount of oxygen required during resting period to restore muscle to normal conditions

What are the mechanisms What are the mechanisms by which muscle fibers by which muscle fibers obtain energy to power obtain energy to power

contractions?contractions?

Muscles and Fiber TypesMuscles and Fiber TypesWhite muscle : White muscle : (glycolytic(glycolytic))

mostly fast fibersmostly fast fiberspale (pale (e.g.,e.g., chicken breast) chicken breast)

Red muscleRed muscle: : (oxidative)(oxidative)mostly slow fibersmostly slow fibersdark (dark (e.g.,e.g., chicken legs) chicken legs)

Most human muscles:Most human muscles:mixed fibersmixed fiberspinkpink

Fast versus Slow FibersFast versus Slow Fibers

Type I

Type II

Abundant mitochondriaAbundant mitochondria Extensive capillary supplyExtensive capillary supply High concentrations of myoglobinHigh concentrations of myoglobin Can contract for long periods of timeCan contract for long periods of time Fatigue resistantFatigue resistant Obtain their ATP mainly from Obtain their ATP mainly from FA FA --

oxidation,oxidation, TCA cycle, and the ETC TCA cycle, and the ETC

Slow fibers:Slow fibers:

Large glycogen reservesLarge glycogen reserves Relatively few mitochondriaRelatively few mitochondria Produce rapid, powerful contractions of Produce rapid, powerful contractions of

short durationshort duration Easily fatiguedEasily fatigued Obtain their ATP mainly from Obtain their ATP mainly from Anaerobic Anaerobic

glycolysisglycolysis

Fast fibersFast fibers

ENERGY REQUIREMENTS ENERGY REQUIREMENTS AND SOURCE OF ENERGY AND SOURCE OF ENERGY FOR SKELETAL MUSCLEFOR SKELETAL MUSCLE

( Resting vs. Working)( Resting vs. Working)

ATP Use in the Resting Muscle CellATP Use in the Resting Muscle Cell

ATP is necessary for cellular housekeeping duties, ATP is necessary for cellular housekeeping duties, e.g.:e.g.:ATP is used for ATP is used for glycogenesisglycogenesis (storage form of (storage form of

glucose)glucose)ATP is used to create another energy storage ATP is used to create another energy storage

compound called compound called creatine phosphatecreatine phosphate

Resting Muscle and Resting Muscle and the Krebs Cyclethe Krebs Cycle

Resting muscle fibers typically takes up fatty acids Resting muscle fibers typically takes up fatty acids from the blood stream.from the blood stream.

Inside the muscle fiber, the Inside the muscle fiber, the FA’s are oxidized (in the are oxidized (in the mitochondriamitochondria) to produce ) to produce Acetyl-CoAAcetyl-CoA & several & several molecules of NADH and FADH2molecules of NADH and FADH2

Acetyl-CoA will then enter the Acetyl-CoA will then enter the Krebs cycle Krebs cycle (in the (in the mitochondriamitochondria)) COCO22, , ATP,ATP, NADH, FADH2, and NADH, FADH2, and oxaloacetateoxaloacetate

NADH and FADH2 will enter NADH and FADH2 will enter the Electron Transport the Electron Transport Chain. Chain. (in the inner (in the inner mitochondrialmitochondrial membrane) membrane) synthesis of synthesis of ATPATP

Figure 10–20a

ATP use in ATP use in Working MuscleWorking Muscle As we begin to exercise, we almost immediately As we begin to exercise, we almost immediately

use our stored ATPuse our stored ATP

For the For the next 15 secondsnext 15 seconds or so, we turn to the or so, we turn to the creatine-phosphate.creatine-phosphate.

This system dominates in events such as This system dominates in events such as the 100m dash or lifting weights.the 100m dash or lifting weights.

Working MuscleWorking Muscle After the phosphagen system is depleted, the muscles After the phosphagen system is depleted, the muscles

must find another ATP source.must find another ATP source. **The process of The process of anaerobic metabolism anaerobic metabolism can maintain ATP can maintain ATP

supply for supply for about 45-60s.about 45-60s. Glycogen Glycogen Glucose Glucose 2 2 pyruvic acid pyruvic acid (2 ATP + 2 NADH)(2 ATP + 2 NADH) 2 Pyruvic acid 2 Pyruvic acid 2 2 lactic acid lactic acid (2 NAD(2 NAD++)) Lactic acid diffuses out of muscles Lactic acid diffuses out of muscles blood blood taken by taken by

the liver the liver Glucose (by gluconeogenesis) Glucose (by gluconeogenesis) blood blood taken by the muscle againtaken by the muscle again

* * It usually takes a little time for the respiratory and cardiovascular It usually takes a little time for the respiratory and cardiovascular systems to catch up with the muscles and supply Osystems to catch up with the muscles and supply O22 for aerobic for aerobic metabolism.metabolism.

Muscle MetabolismMuscle Metabolism

Figure 10–20c

Anaerobic Metabolism, Anaerobic Metabolism, continuedcontinued……

Anaerobic metabolism is inefficient… Why?Anaerobic metabolism is inefficient… Why?Large amounts of glucose are used for very small Large amounts of glucose are used for very small

ATP returns.ATP returns.Lactic acid is produced whose presence Lactic acid is produced whose presence

contributes to muscle fatiguecontributes to muscle fatigue

Which type of sports uses anaerobic Which type of sports uses anaerobic metabolism?metabolism?Sports that requires bursts of speed and activity, Sports that requires bursts of speed and activity,

e.g., basketball.e.g., basketball.

Aerobic MetabolismAerobic Metabolism Occurs when the respiratory and cardiovascular Occurs when the respiratory and cardiovascular

systems have “caught up with” the working muscles.systems have “caught up with” the working muscles. Prior to this, some aerobic respiration will occur thanks to Prior to this, some aerobic respiration will occur thanks to

the muscle protein, the muscle protein, myoglobinmyoglobin, which binds and stores , which binds and stores oxygen.oxygen.

During During restrest and and light to moderate light to moderate exercise, exercise, aerobic metabolism contributes 95% of the aerobic metabolism contributes 95% of the necessary ATP.necessary ATP.

Compounds which can be aerobically metabolized Compounds which can be aerobically metabolized include:include: Fatty acids, Fatty acids, Pyruvic acid (made via glycolysis), and Pyruvic acid (made via glycolysis), and

amino acids.amino acids.

THE CORI CYCLETHE CORI CYCLE&&

THE GLUCTHE GLUCOOSE-SE-ALANINE CYCLEALANINE CYCLE

The Cori cycleThe Cori cycleLiverLiver converts converts lactatelactate into into

glucoseglucose via via gluconeogenesisgluconeogenesis

The newly formed glucose The newly formed glucose is transported to muscle to is transported to muscle to be used for energy againbe used for energy again

The glucose-alanine The glucose-alanine cyclecycle

Muscles produce:Muscles produce: PyruvatePyruvate from glycolysis during exercise and from glycolysis during exercise and NH2 NH2

produced from normal protein degradation produced from normal protein degradation produce produce AlanineAlanine

Pyruvate + NH2 Alanine

This alanine is transported through the blood to This alanine is transported through the blood to liverliver

Liver converts alanine back to pyruvateLiver converts alanine back to pyruvate

Alanine – NH2 = Pyruvate

Pyruvate is used in gluconeogenesisPyruvate is used in gluconeogenesis The newly formed glucose is transported to The newly formed glucose is transported to

muscle to be used for energy againmuscle to be used for energy again

The Glucose-Alanine The Glucose-Alanine CycleCycle

What happened to NHWhat happened to NH22??Liver converts it to urea Liver converts it to urea for excretion (urea cycle)for excretion (urea cycle)