Physiology of Training

Specificity principle

Training adaptations are specific to muscles, movements, and energy systems trained

Specificity example

400 m runner trains mainly ATP-PC and glycolytic systems

Overload principle

Adaptation requires stimulus above normal levels

Progression principle

Gradually increase training demands

10% rule

Increase training volume or intensity by no more than 10% per week

Reversibility principle

Training adaptations are lost when training stops

Tedium principle

Variation helps prevent boredom

Initial values principle

Less fit individuals improve more rapidly

Interindividual differences

People respond differently to training

VO2 equation

VO2 = Q × a-vO2 difference

Q equation

Q = Heart Rate × Stroke Volume

Initial VO2max improvement

Caused mainly by increased maximal cardiac output

Long-term VO2max improvement

Increased cardiac output and a-vO2 difference

Time for initial VO2max changes

1-4 months

Time for long-term VO2max changes

32+ months

Primary reason endurance training increases Qmax

Increased maximal stroke volume

Can endurance training increase HRmax?

No

Preload

Amount of blood filling the ventricle before contraction

EDV

End-diastolic volume

Endurance training effect on preload

Increases preload

Reason lower HR increases preload

More ventricular filling time

Plasma volume expansion

Increases blood volume

Athlete's heart

Physiological left ventricular hypertrophy from endurance training

LV hypertrophy effect

Increases EDV and contractility

Endurance muscle adaptations

Increased mitochondria, capillaries, oxidative fibers, antioxidants, fat use, buffering

Mitochondrial biogenesis

Creation of new mitochondria

Mitophagy

Removal of damaged mitochondria

Mitochondrial location

20% subsarcolemmal, 80% intermyofibrillar

Primary mitochondrial adaptation

Increased size rather than number

Benefit of increased mitochondrial volume

Greater oxidative phosphorylation capacity

Effect on glycolysis

Reduced dependence on glycolysis

Capillary density adaptation

Increases oxygen delivery and waste removal

Fiber type shift with endurance training

Fast-to-slow

Oxidative phenotype

More aerobic characteristics

Mechanical efficiency

Improved after endurance training

Free radicals

Reactive molecules that can damage cells

Endogenous antioxidants

Produced within the body

Exogenous antioxidants

Obtained from diet

Training effect on antioxidants

Increases endogenous antioxidant production

Fuel utilization after endurance training

Greater fat use, less carbohydrate use

FFA

Free fatty acids

GLUT4

Glucose transporter increased with training

Benefit of greater fat utilization

Preserves glycogen stores

Acid-base adaptation

Improved buffering and reduced H+ accumulation

LDH adaptation

Shift to lower affinity pyruvate isoform

Effect on pH

Better maintenance during exercise

Endurance detraining VO2max decline

Within 2 weeks

Reason VO2max falls quickly

Loss of plasma volume and stroke volume

Mitochondrial decline during detraining

More gradual

Retraining effect

Can restore lost adaptations

Submaximal exercise after endurance training

Same VO2 but achieved more efficiently

Steady-state after training

Reached faster

Oxygen deficit after training

Smaller

Lactate production after training

Reduced

PC depletion after training

Reduced

Ventilation during submaximal exercise

Lower

Sympathetic activation after training

Lower

Strength gains early in training

Primarily neural

Strength gains later in training

Muscle hypertrophy

Neural adaptations to strength training

Improved recruitment, synchronization, firing rate

Motor unit synchronization

More units activated simultaneously

Motor neuron firing rate

More action potentials per second

Neural inhibition

Reduced with training

Agonist

Prime mover muscle

Antagonist

Muscle opposing movement

Strength training effect on antagonist activity

Reduced co-activation

Hypertrophy

Increase in muscle fiber size

Hyperplasia

Increase in number of muscle fibers

Primary mechanism of muscle growth

Hypertrophy

Muscle proteins increased during hypertrophy

Actin and myosin

Fiber type most affected by hypertrophy

Type II fibers

Strength training fiber shift

IIx to IIa

Strength training oxidative changes

Possible but evidence inconclusive

Strength training antioxidant effect

Increases endogenous antioxidants

Additional strength training benefits

Stronger tendons, ligaments, bones

Bone adaptation

Increased osteoblast activity and bone density

Collagen synthesis

Increased with strength training

Requirement for hypertrophy

Muscle protein synthesis must exceed breakdown

Time course of hypertrophy

Several weeks

Strength detraining

Loss of strength occurs gradually