Powers, Chapter 13
The Physiology of Training
Effect on VO2max, Performance,
Homeostasis, and Strength
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
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
Calculation of VO2max
• Product of maximal cardiac output (Q) and
arteriovenous difference (a-vO2)
VO2max = HRmax x SVmax x (a-vO2)max
• Improvements in VO2max
– 50% due to  SV
– 50% due to  a-vO2
• Differences in VO2max in normal subjects
– Due to differences in SVmax
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
Figure 12-11
6
Factors Increasing Stroke Volume
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
Summary of Factors Causing Increased VO2max
Detraining and VO2max
• Decrease in VO2max
with cessation of
training
–  SVmax ,  maximal
a-vO2 difference
• Opposite of training
effect
Endurance Training: Effects on
Performance
• Improved performance following endurance
training
• Structural and biochemical changes in muscle
–  Mitochondrial number,  Enzyme activity
–  Capillary density
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
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
Time-course of Training/Detraining
Mitochondrial Changes
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)
Changes in CS Activity Due to
Different Training Programs
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
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
Endurance Training Reduces the O2
Deficit at the Onset of Work
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
Biochemical Changes, FFA Oxidation,
and Glucose-Sparing
Blood Lactate Concentration
• Balance between lactate
production and removal
• Lactate production during exercise
– NADH, pyruvate, and LDH in the
cytoplasm
pyruvate + NADH
LDH
lactate + NAD
• Blood pH affected by blood
lactate concentration
Mitochondrial and Biochemical
Adaptations and Blood pH
Biochemical Adaptations and Lactate
Removal
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
Link Between Muscle and Systemic
Physiology: One Leg Training Study
Peripheral Control of Cardiorespiratory
Responses to Exercise
Central Control of Cardiorespiratory
Responses to Exercise
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
Neural and Muscular Adaptations to
Resistance Training