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

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?

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

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

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

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

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.

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.

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.

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

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.

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.

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

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.

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.

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.

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

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.

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.

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.

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].

Deficit and EPOC

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.

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

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

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.