The Physiology of Training

Performance Effect on VO2max and Strength

Chapter 13

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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

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Calculation of VO2max

Product of maximal cardiac output (Q) and arteriovenous difference (a-vO2)

a-vO2 difference

– Represents amount of oxygen taken into muscle tissue

– Known from PO2 in arterial and venous blood

– Greater difference = more O2 extracted

VO2max = HRmax x SVmax x (a-vO2)max

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Questions:

Can VO2max be improved?

How much can it be improved?

What change influences it the most?

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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

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a-vO2 Difference and Increased VO2max

Improved ability of the muscle to extract oxygen from the blood:– 1. Muscle blood flow (delivery)

Capillary density (delivery)

– 2. Mitochondial number

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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

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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

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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

Endurance training production – FFA use instead of glycolysis– H isoform of LDH = low affinity for pyruvate

removal– Malate-aspartate shuttle = NADH to mitochondria

pyruvate + NADH lactate + NADLDH

Detraining and VO2max

Decrease in VO2max with cessation of training SVmax

maximal a-vO2 difference

(Opposite of training effect)

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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