The Physiology of Training

1. Powers, Chapter 13 The Physiology of Training Effect on VO2max, Performance, Homeostasis, and Strength

2. Principles of Training • Overload 足夠的負荷 • Training effect occurs when a system is exercised at a level beyond which it is normally accustomed • Specificity 專一性 • Training effect is specific to the muscle fibers involved • Type of exercise • Reversibility 回復性 • Gains are lost when overload is removed

3. Endurance Training and VO2max • Training to increase VO2max • Large muscle groups, dynamic activity • 20-60 min, 3-5 times/week, 50-85% VO2max • Expected increases in VO2max • 15% (average) - 40% (strenuous or prolonged training) • Greater increase in highly deconditioned or diseased subjects • Genetic predisposition • Accounts for 40%-66% VO2max

4. Calculation of VO2max • Product of maximal cardiac output (Q) and arteriovenous difference (a-vO2) • Improvements in VO2max • 50% due to  SV • 50% due to  a-vO2 • Differences in VO2max in normal subjects • Due to differences in SVmax VO2max = HRmax x SVmax x (a-vO2)max

5. Stroke Volume and Increased VO2max • Increased SVmax •  Preload (EDV, end diastolic volume) •  Plasma volume •  Venous return •  Ventricular volume •  Afterload (TPR, total peripheral resistance) •  Arterial constriction •  Maximal muscle blood flow with no change in mean arterial pressure •  Contractility 收縮能力

6. Figure 12-11

7. Factors Increasing Stroke Volume

8. a-vO2 Difference and Increased VO2max • Improved ability of the muscle to extract oxygen from the blood •  Muscle blood flow •  Capillary density •  Mitochondial number • Increased a-vO2 difference accounts for 50% of increased VO2max

9. Summary of Factors Causing Increased VO2max

10. Detraining and VO2max • Decrease in VO2max with cessation of training •  SVmax,  maximal a-vO2 difference • Opposite of training effect

11. Endurance Training: Effects on Performance • Improved performance following endurance training • Structural and biochemical changes in muscle •  Mitochondrial number,  Enzyme activity •  Capillary density

12. Structural and Biochemical Adaptations to Endurance Training •  Mitochondrial number  •  Oxidative enzymes • Krebs cycle (citrate synthase) • Fatty acid (-oxidation) cycle • Electron transport chain •  NADH shuttling system • Change in type of LDH • Adaptations quickly lost with detraining

13. Detraining: Time Course of Changes in Mitochondrial Number • About 50% of the increase in mitochondrial content was lost after one week of detraining • All of the adaptations were lost after five weeks of detraining • It took four weeks of retraining to regain the adaptations lost in the first week of detraining

14. Time-course of Training/Detraining Mitochondrial Changes

15. Effect of Exercise Intensity and Duration on Mitochondrial Enzymes • Citrate synthase (CS) • Marker of mitochondrial oxidative capacity • Light to moderate exercise training • Increased CS in high oxidative fibers (Type I and IIa) • Strenuous exercise training • Increased CS in low oxidative fibers (Type IIb)

16. Changes in CS Activity Due to Different Training Programs

17. Influence of Mitochondrial Number on ADP Concentration and VO2 • [ADP] stimulates mitochondrial ATP production • Increased mitochondrial number following training • Lower [ADP] needed to increase ATP production and VO2

18. Biochemical Adaptations and Oxygen Deficit • Oxygen deficit is lower following training • Same VO2 at lower [ADP] • Energy requirement can be met by oxidative ATP production at the onset of exercise • Results in less lactic acid formation and less PC depletion

19. Endurance Training Reduces the O2 Deficit at the Onset of Work

20. Biochemical Changes and FFA Oxidation • Increased mitochondrial number and capillary density • Increased capacity to transport FFA from plasma to cytoplasm to mitochondria • Increased enzymes of -oxidation • Increased rate of acetyl CoA formation • Increased FFA oxidation • Spares muscle glycogen and blood glucose

21. Biochemical Changes, FFA Oxidation, and Glucose-Sparing

22. LDH pyruvate + NADH lactate + NAD Blood Lactate Concentration • Balance between lactate production and removal • Lactate production during exercise • NADH, pyruvate, and LDH in the cytoplasm • Blood pH affected by blood lactate concentration

23. Mitochondrial and Biochemical Adaptations and Blood pH

24. Biochemical Adaptations and Lactate Removal

25. Links Between Muscle and Systemic Physiology • Biochemical adaptations to training influence the physiological response to exercise • Sympathetic nervous system ( E/NE) • Cardiorespiratory system ( HR,  ventilation) • Due to: • Reduction in “feedback” from muscle chemoreceptors • Reduced number of motor units recruited • Demonstrated in one leg training studies

26. Link Between Muscle and Systemic Physiology: One Leg Training Study

27. Peripheral Control of Cardiorespiratory Responses to Exercise

28. Central Control of Cardiorespiratory Responses to Exercise

29. Physiological Effects of Strength Training • Strength training results in increased muscle size and strength • Neural factors • Increased ability to activate motor units • Strength gains in initial 8-20 weeks • Muscular enlargement • Mainly due enlargement of fibers (hypertrophy) • Long-term strength training

30. Neural and Muscular Adaptations to Resistance Training