Chapter 7 Metabolic Responses and Adaptations to Training

1. Chapter 7Metabolic Responses and Adaptations to Training

2. Introduction • Definitions • Metabolism: sum of all chemical reactions in the human body to sustain life • Exergonic reactions: result in energy release • Endergonic reactions: result in stored or absorbed energy • Bioenergetics: flow of energy change within human body • Energy • Ability to perform work • Changes in proportion to magnitude of work performed • Chemical energy needed for several metabolic processes

3. Adenosine Triphosphate (ATP) and Metabolic Systems • Overview • Body requires continuous chemical energy for life & exercise • Potential energy transferred from storage or food to fuel muscle • ATP • High-energy compound used to fuel body • Composed of adenine & ribose (adenosine) + 3 phosphates • Hydrolysis: cleavage of phosphate bond releases energy • ATP + H2O  ADP + Pi + energy

4. Adenosine Triphosphate (ATP)

5. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Three Ways Energy Can Be Used Quickly • Skeletal muscle ATP stores • Capacity: a few seconds of exercise • Phosphocreatine (PC) system • Capacity: 5-10 seconds of high-intensity exercise • PC stored in skeletal muscle (×4 > than ATP) • ADP + phosphocreatine  ATP + creatine • Production of ATP from multiple ADP sources • Capacity: >10 seconds of exercise • 2 ADP  ATP + AMP

6. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Phosphagen Repletion • ATP-PC resynthesis is critical to explosive exercise performance • High-intensity exercise depletes PC by: • 60-80% in first 30 seconds • 70% in first 12 seconds • Longer-duration high-intensity exercise reduces PC by 89% • Greater the PC degradation, the longer the time to recover PC • Biphasic response: faster + slower components • Factors: intensity, volume, muscle pH, ADP level, O2 availability

7. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Anaerobic Training Adaptations • Positive adaptations in ATP-PC & adenylate kinase metabolic systems • Occur in three ways: • Greater substrate storage at rest • Altered enzyme activity • Limited accumulations of fatiguing metabolite

8. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Glycolysis • Breakdown of CHOs to resynthesize ATP in cytoplasm • Anaerobic metabolic system • Capacity: 2 min of high-intensity exercise • Rate of ATP resynthesis not as rapid as that of PC • Larger glycogen than PC supply in body • Gluconeogenesis: reforming of glucose in opposite direction of glycolysis

9. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Control of Glycolysis • Inhibited by: • Sufficient oxygen levels (steady-state exercise & rest) • Reductions in pH • Increased ATP, PC, citrate, & free fatty acids • Stimulated by: • High concentrations of ADP, Pi, & ammonia • Slight decreases in pH & AMP • Regulated by enzyme control & negative feedback systems

10. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Glycogen Metabolism • Muscle glycogen = quick source of glucose • > glycogen availability preexercise  endurance performance • Glycogen use: • Most rapid at beginning of exercise • Increases exponentially as intensity increases • Muscle & liver glycogen repletion: • Critical to recovery after exercise • Factors: hormonal action, glucose uptake, blood flow, CHOs consumed

11. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Training Adaptations • Changes in substrate storage & enzyme activity • Aerobic training (AT): muscle glycogen in FT & ST fibers • Steady-state AT & high-intensity interval training: muscle glycogen storage • Sprint training: may not change or increase glycogen content • RT: increases resting glycogen content by up to 112%

12. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Lactate • Negative impact on performance • Lactate production from pyruvate contributes to muscle fatigue

13. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Metabolic Acidosis and Buffer Capacity • Blood & muscle pH decrease during & after anaerobic exercise • Acidosis: • Adversely affects energy metabolism & force production • Causes onset of fatigue to be rapid • Buffering capacity: • Ability to resist changes in pH • Increased after 7-8 weeks of sprint training • Greater in trained than in untrained people

14. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Aerobic Metabolism • Occurs when adequate oxygen is available • Is primary source of ATP: • At rest • During low to moderate steady-state exercise • Majority of energy comes from oxidation of CHOs & fats • Krebs cycle • Continues oxidation of acetyl CoA • Produces 2 ATP indirectly

15. Krebs Cycle

16. The Electron Transport Chain

17. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Energy Yield From Carbohydrates • 3 ATP produced per molecule of NADH • 2 ATP produced from FADH2 • Glucose oxidation: total of 38 or 39 ATP produced • 2 ATP from blood glucose glycolysis OR 3 ATP from stored glycogen glycolysis • 2 ATP from Krebs cycle • 12 ATP from 4 NADH produced from glycolysis & pyruvate conversion to acetyl CoA • 22 ATP from electron transport chain

18. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Energy Yield From Fats • Fat metabolism predominates at rest & in low/moderate exercise • Lipolysis: breakdown of fats by hormone-sensitive lipase into: • Glycerol • 3 free fatty acids • Fatty acids enter circulation or are oxidized from muscle stores via beta oxidation • Beta oxidation: splitting of 2-carbon acyl fragments from a long chain of fatty acids • People with high aerobic capacity can oxidize fats at a large rate

19. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Aerobic Training Adaptations • # of capillaries surrounding each muscle fiber • Capillary density: # of capillaries relative to muscle CSA • Nutrient & oxygen exchange during exercise • Reliance on fat metabolism • # of mitochondria & mitochondrial density in muscle • Myoglobin content • Enzyme activity • Muscle glycogen stores at rest

20. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Anaerobic Training Adaptations • # of capillaries surrounding each muscle fiber • No change in capillary density (&  with hypertrophy) • Mitochondrial density in muscle • No change in myoglobin content • No change or enzyme activity

21. Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) • Energy System Contribution and Athletics • All energy systems are engaged at all times • Some predominate based on exercise: • Intensity • Volume/duration • Recovery intervals • Training systems can be designed to target each system

22. Metabolic Demands and Exercise • Indirect Calorimetry • Measurement of O2 consumption via open-circuit spirometry • Changes in O2 & CO2 %’s in expired air compared with normal, inspired ambient air • Components: flow meter, computer interface • Measure of energy expenditure • Respiratory quotient: measure of CO2 produced per unit of O2

23. Metabolic Demands and Exercise (cont’d) • Basal Metabolic Rate (BMR) • Minimal level of energy needed to sustain bodily functions • Factors affecting BMR: • Body mass • Regular exercise • Diet-induced thermogenesis • Environment

24. Metabolic Demands and Exercise (cont’d) • Estimating Resting Energy Expenditure • Important for weight loss/gain programs • Several population-specific equations developed • Predictor variables: body mass or LBM, height, age • Equations • Harris & Benedict • Mifflin-St Jeor • Cunningham

25. Metabolic Demands and Exercise (cont’d) • Estimating Energy Expenditure During Exercise • Average energy expenditure at rest: • 0.20-0.35 L of O2 min-1 • 1.0-1.8 kcal min-1 • In metabolic equivalents (METs): • Men: 250 mL min-1 • Women: 200 mL min-1 • Exercise increases energy expenditure based on intensity, volume, muscle mass involvement, rest intervals

26. Metabolic Demands and Exercise (cont’d) • Oxygen Consumption and Acute Training Variables • O2 consumption • Increases during exercise in proportion to intensity • Increases exponentially as exercise approaches steady state • Remains elevated during recovery after exercise • O2 deficit • Difference between O2 supply & demand • Larger during anaerobic than aerobic exercise • Smaller in aerobically trained athletes than in untrained & strength/power athletes

27. Oxygen Consumption During Exercise and Excess Postexercise Oxygen Consumption

28. Metabolic Demands and Exercise (cont’d) • Resistance Exercise and Oxygen Consumption • Resistance exercise increases VO2 during & after a workout • VO2: • Greater during large muscle-group exercises than smaller • Varies based on lifting velocity • Greater when exercises are performed with high intensity • Greater when exercises are performed for high rep # • Greater when exercises are performed with short rest intervals • Not affected by exercise order

29. Metabolic Demands and Exercise (cont’d) • Body Fat Reductions • Require proper diet & exercise • Energy expenditure must exceed energy intake for net kilocalorie deficit • Dietary recommendations: • Well-balanced diet from major food groups • High water intake • 55-60% of kcal from CHOs • 15% of kcal from protein • <25% of kcal fats