1. Energy Transfer During Exercise
McArdle, Katch, & Katch
Chapter 6

2. Immediate Energy: The ATP-PC System
Immediate & rapid supply of energy almost exclusively from high energy phosphates ATP and PCr within specific muscles.
How much stored within muscles?

3. Immediate Energy: phosphagens
ATP = 5 mmol/kg
PCr = 15 mmol/kg
For 57 kg female (20 kg muscle) = 400 mmol total
For 70 kg male (30 kg muscle) = 600 mmol total
Brisk Walk
Slow Jog
All-out Sprint
1 minute
20 – 30 sec.
6 – 8 seconds

4. Immediate Energy: phosphagens
Activities that rely almost exclusively on stored phosphagens:
Wrestling
Apparatus routines in gymnastics
Weight lifting
Most field events
Baseball
Volleyball

5. Short-Term Energy: Lactic Acid System
To continue strenuous exercise beyond a brief period, the energy to phosphorylate ADP comes from glucose and stored glycogen during anaerobic process of glycolysis

6. Short-Term Energy: Lactic Acid System
This occurs when oxygen supply is
Inadequate or
Oxygen demands exceed oxygen utilization
Activities powered mainly by lactic acid energy system
Last phase of mile run, 400 m run
100 m swim
Multiple sprint sports: ice hockey, field hockey, and soccer

7. Short-Term Energy: Lactic Acid System
Blood Lactate Accumulation
Only when lactate removal (Ld < La) is slower than lactate production does lactate accumulate.
During light & moderate exercise, aerobic metabolism meets energy demands. Non-active tissue rapidly oxidize any lactate formed.

8. Short-Term Energy: Lactic Acid System
Lactate begins to rise exponentially at about 55% of healthy untrained person’s max VO2.
Usual explanation is relative tissue hypoxia.
Point of abrupt increase in blood lactate is onset of blood lactate accumulation.

9. Short-Term Energy: Lactic Acid System
Blood lactate threshold occurs at higher percentage in trained individual’s capacity due to:
Genetic endowment, e.g. muscle fiber type, or
Local adaptations that favor less production of HLa and more rapid removal rate. Endurance trg. extends exercise intensity before OBLA.
Lactate formed in one part of an active muscle can be oxidized by other fibers in same muscle or by less active neighboring muscle tissue.

10. Short-Term Energy: Lactic Acid System
Blood lactate as an Energy Substrate
Substrate for Gluconeogenesis in liver
Lactate shuttling between cells – supply fuel

11. Short-Term Energy: Lactic Acid System
Ability to generate high lactate concentration in maximal exercise increases with specific sprint and power training.
An anaerobically trained athlete can accumulate 20 to 30% more blood lactate compared to untrained subjects.
Possible reasons:
Increased intramuscular glycogen stores, 20% increase glycolytic enzymes, motivation.

12. Long Term Energy: the Aerobic System
The use of oxygen by cells is called oxygen uptake (VO2).
Oxygen uptake rises rapidly during the first minute of exercise.
Between 3rd and 4th minute a plateau is reached and VO2 remains relatively stable.
Plateau of oxygen uptake is known as steady rate.

13. Long Term Energy: Aerobic System
Steady-rate is balance of energy required and ATP produced.
Any lactate produced during steady-rate oxidizes or reconverts to glucose.
Many levels of steady-rate in which: O2 supply = O2 demand.
Oxygen supply requires
Deliver adequate oxygen to muscles
Process oxygen within muscles

14. The Aerobic System
Oxygen Deficit: difference between total oxygen consumed during exercise and amount that would have been used at steady-rate of aerobic metabolism.

15. Oxygen Deficit
Energy provided during the oxygen deficit phase represents a predominance of anaerobic energy transfer from stored intramuscular phosphagens plus rapid glycolytic reactions.
Steady-rate oxygen uptake during light & moderate intensity exercise is similar for trained & untrained.
Trained person reaches steady-rate quicker, has smaller oxygen deficit.

16. Maximum Oxygen Uptake
The point when VO2 plateaus with additional workloads.
Maximum VO2 indicates an individual’s capacity for aerobic resynthesis of ATP.
Additional exercise above the max VO2 can be accomplished by anaerobic glycolysis.

17. Fast- and Slow-Twitch Fibers
Fast Twitch Fibers (II)
Slow Twitch Fibers (I)
Fast Contraction Speed
Half as Fast as FT
High Anaerobic Capacity
High Aerobic Capacity: mitochondrial density, aerobic enzymes

18. The Energy Spectrum
Relative contribution of aerobic & anaerobic energy during maximal physical effort.
Intensity and duration determine the blend.
Nutrient-related Fatigue: severe depletion glycogen.

19. Oxygen Uptake during Recovery
Light aerobic exercise rapidly attains steady-rate with small oxygen deficit.
Moderate to heavy aerobic takes longer to reach steady-rate and oxygen deficit considerably larger.
Maximal exercise (aerobic-anaerobic) VO2 plateaus without matching energy requirement.

20. Oxygen Uptake during Recovery
Four reasons why excess post-exercise oxygen consumption (EPOC) takes longer to return to baseline following strenuous
Oxygen deficit is smaller in moderate exercise
Steady-rate oxygen uptake is achieved versus in exhaustive exercise never attained
Lactic acid accumulates in strenuous exercise
Body temperature increased considerably more.

21. Oxygen Uptake during Recovery
Traditional “Oxygen Debt” Theory
Alactacid oxygen debt: restoration of ATP & PCr depleted during exercise, small portion to reload muscle myoglobin & hemoglobin [fast].
Lactacid oxygen debt: to re-establish original glycogen stores by resynthesizing 80% HLa through gluconeogenesis (Cori cycle) and to catabolize remaining HLa through pyruvic acid (Kreb’s cycle) [slower phase].

22. Deficit and EPOC

23. Oxygen Uptake during Recovery
Updated Theory because disprove traditional Oxygen Debt Theory.
EPOC serves to replenish high-energy phosphates and some to resynthesize a portion of lactate to glycogen.
Significant portion EPOC attributed to thermogenic boost that stimulates metabolism (Q10).
Other factors EPOC: 10% reloads blood O2; 2-5% restores O2 in body fluids, including myoglobin; all systems increased O2 need in recovery due to effects of epinephrine, norepinephrine, and thyroxine.

24. Oxygen Uptake during Recovery
Time frame for lactate removal post-exercise
Mass action effect: rate proportional to amount of substrate & product present
Passive or Active Recovery
Optimum recovery steady-rate exercise: passive
Optimum recovery non-steady rate: active

25. Oxygen Uptake during Recovery
Intermittent Exercise: interval training
Major advantage of interval training: enable performance of large amounts of exhaustive exercise & lower HLa
Exercise: Recovery Ratio
1:3 ratio overloads immediate energy system
1:2 ratio to train short-term glycolytic system
1:1 ratio to train long-term aerobic system

26. Illustration References
Axen and Axen Illustrated Principles of Exercise Physiology. Prentice Hall.
McArdle, William D., Frank I. Katch, and Victor L. Katch Essentials of Exercise Physiology 4th ed. Image Collection. Lippincott Williams & Wilkins.
Plowman, Sharon A. and Denise L. Smith Digital Image Archive for Exercise Physiology. Allyn & Bacon.