Energy Transfer During Exercise

1. Energy TransferDuring 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

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

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. 2001. Illustrated Principles of Exercise Physiology. Prentice Hall. • McArdle, William D., Frank I. Katch, and Victor L. Katch. 2011. Essentials of Exercise Physiology 4th ed. Image Collection. Lippincott Williams & Wilkins. • Plowman, Sharon A. and Denise L. Smith. 1998. Digital Image Archive for Exercise Physiology. Allyn & Bacon.