Three Metabolic Pathways

PSK 4U Unit 5: Energy Systems Days 2-3

The Energy Systems

The ability to move, work or play sports is dependant on supplying sufficient energy at the required rate for the duration of the

activity.

All energy in the human body comes from the breakdown of complex nutrients like

carbohydrates, fats and proteins.

Biologic Energy Cycle Energy can neither be created or destroyed but merely transformed.

Plants

Carbohydrates Proteins

Chemical Energy

Sun = Solar Energy.

Animals

Carbohydrates Proteins Fats

Chemical / Mechanical Energy Humans

Carbohydrates, Proteins, Fats, ATP – PC.

Chemical / Mechanical Energy

O2

CO2 H2O

Bioenergetic Conversion

• The breakdown of energy nutrients for energy to carry out physical activity.

Carbohydrates Fats Proteins

4.1 cal/gram 9.3 cal/gram 4.3 cal/gram

Glycogen Triglycerides Amino Acids

Glycolysis Lipolysis

Glucose Fatty acids Not stored; excreted through urine

• Carbohydrates are the most abundant substances in nature – they come to us from foods that originate from plants (fruits and vegetables) and grain based products (such as bread and pasta).

• Glycogen = Stored form of glucose within skeletal muscle and the liver.

Review

The end result of nutrient breakdown is the production of various amounts of adenosine triphosphate (ATP).

•ATP is the immediate energy source for muscular contraction.

•An ATP molecule consists of an adenosine molecule bonded to three phosphate groups.

Adenosine Triphospate (ATP)

•ATP molecules are supplied by chemical reactions that take place in the mitochondria found in muscle cells.

Adenosine P P P

Adenosine Triphosphate (ATP)

To release the energy, a phosphate molecule breaks away from the phosphate group through hydrolysis to form adenosine diphosphate (ADP)

Breaking ATP into ADP releases energy and allows

cross bridge formation to occur between the myosin

and actin filaments inside the muscle.

Adenosine Adenosine P P P Hydrolysis P P P

HEAT

ENERGY

ATP is a renewable resource that can be regenerated by the recombination of ADP with a free phosphate. The following reaction describes the regeneration process.

+ +

• To accomplish this synthesis, energy must be available;

• Energy is supplied through the breakdown of complex food molecules, such as fats and carbohydrates.

Adenosine Adenosine P P P P P P ENERGY

The 3 Energy Pathways The production of ATP involves three energy pathways, each

producing ATP at a distinct rate and duration:

1. The Immediate or High Energy Phosphate system (Anaerobic Alactic or ATP- PC system)

2. The Short-Term or Glycolytic system

(Anaerobic Lactic or Lactic Acid system)

3. The Long-Term or Oxygen system (Aerobic)

The three energy pathways are designated as anaerobic or aerobic, depending on whether oxygen is needed by the system in the production of energy.

Two Systems = Three Pathways 1.Anaerobic

• Energy systems that do not rely on the immediate use of oxygen. There are two types of anaerobic energy systems.

Anaerobic Alactic (ATP-CP)

• A short term energy of both fast and slow twitch muscle fibres that does not require oxygen and does not produce lactic acid.

Anaerobic Lactic (glycolysis)

• A fast twitch muscle energy system which does not require the immediate use of oxygen but does produce lactic acid.

2.Aerobic (cellular respiration)

• A slow twitch muscle energy system which is used in prolonged continuous activity in the presence of oxygen and does not produce lactic acid.

ATP-PC (Anaerobic Alactic)

An immediate - high energy phosphate system

Involves high power output activities that require an immediate high rate of energy production for a short period of time.

Involves activities such as weight lifting, high jump, long jump, shot put, discus 50 metre sprint, 25 metre swim.

Adenosine P P P

HEAT

ENERGY

As muscle contraction begin, the body’s metabolism may not be able to supply ATP to the contracting muscle cells as rapidly as required…The body must then make use of creatine phosphate (phosphocreatine). Creatine phosphate serves as a quick available energy reserve for muscles as it is broken down into creatine and phosphate.

+ The free phosphate ions bonds with ADP to produce ATP and leaves behind creatine. The new ATP molecule is stored as potential energy.

ATP ENERGY

Adenosine P P P PC PC

PC PC

PC PC Creatine

Anaerobic Alactic Characteristics

• Only a small amount of ATP and PC is stored in muscle fibres;

• Uses very large amounts of energy in a short period of time;

• The rate of recovery is relatively rapid. After a brief rest (2 minutes or so), the system is recharged and ready for the next sprint;

• Oxygen is not required;

• Glucose is not used;

• Lactic acid is not produced;

• The system can only provide energy for muscles for the first

10-15 seconds of high intense activity;

• Uses both fast and slow twitch muscles;

• Work output is relatively high.

Glycolysis (Anaerobic Lactic)

In all out sprint, which requires a great deal of power output in a short period of time, (15-60 or 120 seconds) ATP cannot be supplied rapidly enough to meet the needs of the muscle cells.

Energy is quickly available, but the anaerobic pathways are not very efficient

• short term energy stores are rapidly depleted,

• lactic acid builds up

• exercise soon comes to a halt.

If an athlete must continue vigorous work a second energy system uses a complex biochemical process which breaks down carbohydrates into glucose and glycogen to release energy.

One molecule of glucose yields:

• two molecules of ATP and

• pyruvate, which is converted to lactic acid in the absence of oxygen.

Carbs

Glucose/glycogen ENERGY

Lactic Acid

ADP + P ATP

The Effects of Lactic Acid

During intense exercise, lactic acid builds up in the blood faster than it can be removed.

• Lactic acid hampers the breakdown of glucose

As lactic acid build up an athlete will reach their Anaerobic

Threshold.

• Anaerobic threshold is the point where a person begins to

feel discomfort and a burning sensation in their muscles.

• At the anaerobic threshold the muscle loses it ability to

contract resulting in muscle fatigue.

• As work increases, the body reaches the

Anaerobic Threshold

• At this point the anaerobic system can no longer keep pace with the increasing requirements of the muscles.

Low

Slow twitch fibres dominate

Exercise Intensity

Moderate

Fast-twitch type A fibres are recruited

The anaerobic threshold is the highest intensity of workload at which lactate clearance still keeps pace with lactate production.

Once this level is reached the intensity level must decrease to reduce the amount of lactic acid buildup

High Fast-twitch Type B fibres

dominate

The Effects of Lactic Acid • Lactic acid causes pH changes in the muscle fibres and they

can no longer respond to stimulation. • Lactic acid interferes with cross- bridge bonding by limiting

the strength of the fibre contraction. • A high production of lactic acid ultimately limits continued

performance in intense activities When lactic acid accumulates, extreme fatigue sets in and oxygen debt develops.

Oxygen debt is the reason you must breathe rapidly and deeply for a few minutes after strenuous exercise.

After you stop anaerobic exercise, your body needs extra oxygen to burn up the excess lactic acid and return your energy reserves to normal.

Lactic acid cannot be removed until extra oxygen is supplied to convert it to harmless, re-usable products.

Oxygen Debt

• Oxygen debt refers to post exercise oxygen consumption where the body needs to pay back its debt incurred above after the exercise is over

• You will notice that even after you are done racing you will continue to breath hard.

• At this point your body is still trying to repay the oxygen debt that was created when you were working hard.

Characteristics of the Lactic Acid System

• The energy source is entirely carbohydrate;

• Oxygen is not required

• Energy is provided for 15-60 or 120 seconds depending on conditioning

• Uses predominately fast twitch muscle fibres

• Work output is moderate

• Used in sports such as football, basketball and hockey.

The Effect of Training on the Lactic Acid System At any level of work, the rate of lactic acid build-up is decreased through training. • The anaerobic threshold rises. • The individual is able to “handle” a higher level of lactic acid. • Trained individuals are able to remove lactic acid faster from

exercising muscles. • Improvements in the cardiovascular system deliver an increased blood

flow to the working muscle.

Raising Your Anaerobic Threshold

Since it is not possible to convert fast twitch fibres to slow twitch fibres, raising your anaerobic threshold depends on improving the condition of the fast twitch muscle fibres. This occurs when effort intensifies. How do you know if your workouts are pushing your AT? • Pay attention to how your running feels. • After several workouts, you'll notice the feeling when you

are in the anaerobic zone. • Elite athletes use the Conconi test which requires a hand-

held device that directly measures blood lactate concentration. The corresponding heart rate at the AT gives you a convenient way of monitoring your workouts.

End of Day 2

Long-Term Energy: Aerobic System

• As the length of an exercise session continues the athlete requires a steady power output over a long period of time

• Exercise performed at a lower intensity level relies almost

exclusively on the aerobic system for energy production and requires the athlete to use oxygen as its source of energy.

o Most daily activities use energy provided by the aerobic energy

system o The oxygen energy system is the most important energy system in

the body.

• While this pathway cannot generate the speed of the anaerobic, it does provide a great deal more efficiency and endurance.

The Cori Cycle

• The process by which lactic acid is concerted to pyruvate for future conversion to glucose and glycogen

• This gets rid of lactic acid in our system and helps to

contribute to future energy production.

Aerobic System – Cellular Respiration

• The aerobic system energy requires the metabolism of

Glucose (stored in muscles)

Fats

Proteins

Oxygen

Combine to produce

ADP + P ATP

Using energy produces

ENERGY

CO2 Water

Characteristics of the Aerobic System

The oxygen system is highly efficient. When oxygen is used in muscle cells:

• it prevents the build-up of lactic acid

• an individual can work out longer before lactic acid build-up begins

• it is able to remove lactic acid from muscles allowing the muscle to continue to contract allowing exercise to continue

• it promotes the re-synthesis of ATP for energy when work output is low.

As the duration of activity increases, the contribution of the aerobic system to the total energy requirement increases. Due to this, there are two limitations to the aerobic system:

• The system requires a continuous supply of oxygen and fuel sources necessary for the aerobic metabolism.

• The use of ATP must be relatively slow to allow the process to meet the energy demands

Aerobic System Oxygen uptake The power of the aerobic system is generally evaluated by measuring the maximum volume of oxygen that can be consumed in a given amount of time. This can be measured by determining the amount of oxygen exhaled as compared to the amount inhaled. As the intensity of work increases the capacity of aerobic system reaches a maximum. The greatest rate at which oxygen can be taken in and used during exercise is referred to maximal oxygen consumption or (VO2max)

Aerobic Power – VO2 Max

Each person has his or her own maximal rate of oxygen

consumption (VO2 max)

• The maximal rate at which oxygen can be used is genetically determined.

• A normal VO2 max for most high school athletes would fall somewhere between 45 and 60 range.

• The VO2 max values of trained athletes will reach 80-90 for males and 75-85 for females

The more active we are the higher the VO2 max.

Maximal O2 Consumption (VO2 Max) in ml / kg / min. for the 2.4km Run

Time Max Time Max VO2 VO2 8:00 65.2 10:45 48.9 8:15 64.9 11.00 47.6 8:30 63.2 11.15 46.1 8:45 61.3 11:30 44.7 9:00 59.1 11.45 43.2 9:15 57.9 12:00 41.7 9:30 56.7 12:15 40.3 9:45 55.6 12:30 38.9 10:00 53.1 12:45 37.4 10:15 51.8 13:00 36.2 10:30 50.1 13:15 35.1

Oxygen Deficit While exercising intensely the body is sometimes unable to meet all of its energy needs. Specifically, it is unable to take in and absorb enough oxygen to adequately 'feed' the muscles the amounts of energy needed to adequately perform the tasks the athlete is requesting from the body. In order to make up the difference without sacrificing output, the body must tap into its anaerobic metabolism. This is where the body uses both aerobic and anaerobic energy production. While not hugely detrimental, oxygen deficits can grow to a level that the anaerobic energy system cannot cover. This can cause performance to deteriorate.

Effect of Training on the Aerobic System

The performance of any activity requires a certain rate of oxygen consumption. A person’s ability to perform an activity is limited by their maximal rate of oxygen consumption. Therefore, the most efficient method for improving the aerobic energy system is endurance training/exercise. Long, slow distance training or exercise at the low end of your target heart rate tends to use slow twitch fibres. Walking, jogging or any other light exercise, uses mainly slow-twitch fibres to do the work. ST fibres are slower to fatigue and are well suited for endurance activities.

Effect of Training on the Aerobic System

Endurance exercise consists of repeated, sustained effort of long duration several times per week.

Generally, the higher the intensity, the greater the oxygen consumption. When exercising the target heart rate (THR) should be raised to 70% of max. Examples include: running, swimming or biking for 40 minutes or more at a heart rate of 130-140 bpm

Notes: A highly trained or elite athlete should be able to sustain a heart rate of 85% of their VO2 max.

This type of training does not raise your anaerobic threshold.

Endurance training has four major effects on the aerobic system:

• Improved delivery of oxygen and nutrients to the muscles

• Increase the size and number of mitochondria in muscle fibres

• Increased activity of enzymes involved in the aerobic pathway

• Preferential use of fats over glucose during exercise which saves the muscles limited store of glycogen

Using All 3 Pathways

While running at a comfortable pace you use both systems, but the anaerobic: aerobic ratio is low enough that the lactate generated is easily removed, and doesn't build up. As the pace is increased, eventually a point is reached where the production of lactate, by the anaerobic system, is greater than its removal. The anaerobic threshold is the point where lactate (lactic acid) begins to accumulate in the bloodstream. Note: Depending upon the distance, and effort, the body can use different proportions of both of these systems. For example, the 800 m race is too long to be a sprint, but too short to be a distance race. Therefore, it is run at the cross-over between the aerobic and anaerobic systems.

Training the Pathways

The best method to train all of the systems together is interval training. Interval work consists of repeating a series of short, high intensity, runs alternating with rest (recovery) periods. Whichever method is used, the athlete must continually push themselves into a lactate burdened state which makes their body adapt. Regardless of the race distance you are training for, 5k or marathon, interval work will help you run faster. Pushing the body past the 'comfortable' speed of running increases aerobic capacity, trains the fast twitch muscles to operate at a higher /faster level and makes the athlete more tolerant of lactic acid build up. The result of interval training is that a runner who can comfortably run at eight-minute/ mile pace and runs their intervals at a seven-minute/mile pace will be able to increase their steady comfortable pace under an eight-minute/mile pace.

Summary of the Systems

• Energy for muscular activity depends on a supply

of ATP that can be broken down into ADP and

phosphate

• All of the body’s biochemical processes and the

three energy systems require ATP

• Trained individuals are able to use ATP and remove

lactic acid more efficiently than untrained

individuals

• Endurance training can significantly improve the

aerobic system

Energy system Anaerobic Alactic Anaerobic Lactic Aerobic

Type of Activity short sprints used in

baseball, pole vault

long jump triple jump

games such as football,

Basketball, Hockey

long distance running

cross country skiing

swimming

Range of Maximum Work Times

0 – 15 seconds 15 to 60 or 120 seconds (depending on conditioning)

120 seconds plus

Oxygen Required None None or very little Yes

Lactic Acid Produced

None Yes, accumulated faster than it can be removed

Depends on intensity

Energy Source Chemical energy stored in muscles, ATP and CP

Entirely carbohydrate (glycogen)

Mixture of fat, protein and carbohydrate

End Products of Fuel Breakdown

Adenosine Diphosphate Creatine Phosphate plus

energy

Lactic Acid CO2 and H2O

Muscle Fibre Recruited

Fast and slow twitch Predominately fast twitch Slow twitch and some fast twitch

Work Output per Unit of Time

High Medium Low

Comparing the Systems

Anaerobic Pathways Aerobic Pathways

Primary Energy Source

ATP produced without the presence of oxygen

ATP produced with the presence of oxygen

Energy System

Immediate Alactic

Short-term Lactic Long-term Oxygen

Fuel ATP and CP Glycogen + glucose Glycogen, glucose, fat and protein

Duration 0s 10s 40s 70s 2 min 6 min 25 min 1 hr 2hr 3hr

Sport Event

Sprinting

100 m dash

Throwing

Jumping

Weightlifting

Ski jumping

Diving

Vaulting in

Gymastics

Track

200-400 m,

500m

Speedskating

Most

gymnastics

Events,

Cycling(track)

50 m swim

100 m Swim

800 m track

Gymnastic floor

exercise

Alpine skiing

Cycling 1000m

pursuit

Middle

distance track,

swimming,

speedskating

1000 m canoe

Boxing,

Wrestling

Rowing

Figure skating

Cycling pursuit

Long Distance

Track,swimming,

canoeing,

speedskating

Cycling road racing

Marathon

Triathlon

Most team Sports/Racquet Sports

Roles of 3 Pathways in Sports

ATP - CP System

Glycolytic System

Aerobic System

When the systems are used

Feel the burn!

Picture All 3 Pathways

End of Day 3