1. Copyright © 2012 American College of Sports Medicine Chapter 7 Metabolic Responses and Adaptations to Training

2. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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 + H 2 O  ADP + P i + energy

4. Copyright © 2012 American College of Sports Medicine Adenosine Triphosphate (ATP)

5. Copyright © 2012 American College of Sports Medicine Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) Three Ways Energy Can Be Used Quickly 1.Skeletal muscle ATP stores Capacity: a few seconds of exercise 2.Phosphocreatine (PC) system Capacity: 5-10 seconds of high-intensity exercise PC stored in skeletal muscle (×4 > than ATP) ADP + phosphocreatine  ATP + creatine 3.Production of ATP from multiple ADP sources Capacity: >10 seconds of exercise 2 ADP  ATP + AMP

6. Copyright © 2012 American College of Sports Medicine 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, O 2 availability

7. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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, P i, & ammonia Slight decreases in pH & AMP –Regulated by enzyme control & negative feedback systems

10. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) Lactate –Negative impact on performance –Lactate production from pyruvate contributes to muscle fatigue

13. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine Krebs Cycle

16. Copyright © 2012 American College of Sports Medicine The Electron Transport Chain

17. Copyright © 2012 American College of Sports Medicine Adenosine Triphosphate (ATP) and Metabolic Systems (cont’d) Energy Yield From Carbohydrates –3 ATP produced per molecule of NADH –2 ATP produced from FADH 2 –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. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine Metabolic Demands and Exercise Indirect Calorimetry –Measurement of O 2 consumption via open-circuit spirometry –Changes in O 2 & CO 2 %’s in expired air compared with normal, inspired ambient air –Components: flow meter, computer interface –Measure of energy expenditure –Respiratory quotient: measure of CO 2 produced per unit of O 2

23. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine 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. Copyright © 2012 American College of Sports Medicine Metabolic Demands and Exercise (cont’d) Estimating Energy Expenditure During Exercise –Average energy expenditure at rest: 0.20-0.35 L of O 2 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. Copyright © 2012 American College of Sports Medicine Metabolic Demands and Exercise (cont’d) Oxygen Consumption and Acute Training Variables –O 2 consumption Increases during exercise in proportion to intensity Increases exponentially as exercise approaches steady state Remains elevated during recovery after exercise –O 2 deficit Difference between O 2 supply & demand Larger during anaerobic than aerobic exercise Smaller in aerobically trained athletes than in untrained & strength/power athletes

27. Copyright © 2012 American College of Sports Medicine Oxygen Consumption During Exercise and Excess Postexercise Oxygen Consumption

28. Copyright © 2012 American College of Sports Medicine Metabolic Demands and Exercise (cont’d) Resistance Exercise and Oxygen Consumption –Resistance exercise increases VO 2 during & after a workout –VO 2 : 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. Copyright © 2012 American College of Sports Medicine 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