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Chapter 13
The Physiology of Training
.
Performance Effect on VO2max and Strength
Principles of Training

Overload
– Training effect occurs when a system is
exercised at a level beyond which it is
normally accustomed

Specificity
– Training effect is specific to the muscle
fibers involved
– Type of exercise

Reversibility
– Gains are lost when overload is removed
Moffit’s corollary to Principles of
Training

Consistency
– Once in a while is better than nothing…..
but just barely
– Even if just a little overload, as long as
there is consistency there will be positive
changes
Result of Endurance Training

Structural and biochemical changes in
muscle
–  Mitochondrial number
•  Enzyme activity
–  Capillary density
Result of Endurance Training


Ability to perform repeated sub maximal
muscle contractions
Ability to support aerobic energy
production
– For longer periods (duration)
– At higher intensities (work capacity)

Higher
maximal oxygen consumption
.
(VO2max)
.
What is VO2max?


Maximum capacity to use oxygen in the
recycling of ATP
Factors Affecting:
– Delivery of oxygen
• Blood circulation
– Extraction of oxygen
• Unloading
– Use in metabolism
• Mitochondria
.
Calculation of VO2max
.

Product of maximal cardiac output (Q)
and arteriovenous difference (a-vO2)
.
VO2max = HRmax x SVmax x (a-vO2)max

a-vO2 difference
– Represents amount of oxygen taken into
muscle tissue
– Known from PO2 in arterial and venous
blood
– Greater difference = more O2 extracted
Questions:
.

Can VO2max be improved?

How much can it be improved?

What change influences it the most?
Answers:



Yes, it can be improved
It can be increased by up to 15%
.
Improvements in VO2max from:
– 50% due to  a-vO2 difference
– 50% due to  SV
.

Differences in VO2max in untrained
– Due to differences in SVmax
a-vO
Difference
and
Increased
2
.
VO2max

Improved ability of the muscle to extract
oxygen from the blood:
– 1.  Muscle blood flow (delivery)
•  Capillary density (delivery)
– 2.  Mitochondial number
.
Stroke Volume and Increased VO2max

Increased SVmax
–  Preload (EDV)
•  Plasma volume
•  Venous return
•  Ventricular volume
–  Afterload (TPR)
•  Arterial constriction
•  Maximal muscle blood flow with no change in
mean arterial pressure
–  Contractility
Structural and Biochemical
Adaptations to Endurance Training


 Mitochondrial number
 Oxidative enzymes
– Krebs cycle (citrate synthase)
– Fatty acid availability (-oxidation)
– Electron transport chain (cytochromes)



 NADH (shuttling system)
Change in type of LDH (pyruvate unchanged)
Adaptations quickly lost with detraining
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
– More ATP available sooner when trained
Effect of Exercise Intensity and
Duration on Mitochondrial Enzymes

Citrate synthase (CS)
– Marker of mitochondrial oxidative capacity

Light to moderate endurance training
– Increased CS in high oxidative fibers (Type I and IIa)

Strenuous endurance training
– Increased CS in low oxidative fibers (Type IIb)
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
Blood *Lactate Concentration

Lactate production during exercise
pyruvate + NADH

LDH
lactate + NAD
Endurance training  production
– FFA use instead of glycolysis
– H isoform of LDH = low affinity for pyruvate

 removal
– Malate-aspartate shuttle = NADH to mitochondria
.
Detraining and VO2max
.

Decrease in VO2max with cessation of
training
–  SVmax
–  maximal a-vO2 difference
(Opposite of training effect)
Detraining: Time Course of Changes in
Mitochondrial Number: Study Results



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
Time Course of Changes
Associated With Detraining
Physiological Effects of Strength
Training

Neural factors
– Increased ability to activate motor units - recruitment
– Strength gains in initial 8-20 weeks

Muscular enlargement
– Mainly due enlargement of fibers (hypertrophy)
• More sarcomeres in parallel
• More fluid within the cell
– Long-term strength training
Neural and Muscular Adaptations
to Resistance Training
Questions?
End