Training Adaptations

Expansion

Endurance training

• Cardiac: increased stroke volume with eccentric hypertrophy, lower resting and submaximal heart rate, increased plasma volume
• Muscle: increased mitochondrial density, oxidative enzymes, capillary density, myoglobin and fat oxidation capacity
• Result: higher VO2 max and, more importantly for performance, a higher lactate threshold

Resistance training

• Neural adaptations first: better recruitment, firing rate and synchronisation, giving strength gains within 2 to 4 weeks before any size change
• Hypertrophy of type II fibres more than type I, from about 6 to 8 weeks
• Increased tendon and bone strength
• Little change in VO2 max

Detraining is rapid: much of the plasma volume and mitochondrial gain is lost within 2 to 4 weeks of inactivity, whereas strength declines more slowly.

The specificity principle underlies both: adaptations occur in the systems that are stressed, which is why cross-training benefits are limited and why rehabilitation must target the intended function.