Principle of Progressive Overload

For gains in strength and power, the trainee must take on a training load greater than what the body is normally accustomed to. As the body adapts to this new level of force, the training stimulus must be readjusted so that added stress is again placed on the musculoskeletal system. The body responds to an overload by raising its strength threshold; for further improvement to occur, the training resistance must therefore increase again.

Overloading is tied directly to the idea of voluntary maximal contraction: the muscle must contract against a resistance it does not normally encounter, and this process stimulates the physiological changes that increase the strength and size of the muscle (see maximal-muscular-contraction). One way many resistance-training systems guarantee this is by using sets to failure and/or RM loads.

If the body is underloaded for a period — because of illness, bed rest, or simply a lack of training — strength is lost as the threshold level drops (this connects to reversibility-disuse). The overload must be large enough to stimulate adaptation but not so great that it causes injury.

Once strength has been gained through training, it can be maintained with as little as one maximal contraction per week per muscle group. Research has shown strength marginally improving over a 6-week period on such a maintenance program, whereas strength diminishes when training stops altogether.

• Training load must exceed what the body is normally accustomed to.
• Body adapts by raising the strength threshold; resistance must then increase again for continued gains.
• Underloading (illness, bed rest, no training) lowers the threshold and causes strength loss.
• Overload must stimulate adaptation but avoid injury.
• Maintenance: 1 maximal contraction per week per muscle group can hold (and marginally improve over 6 weeks) gained strength.

• maximal-muscular-contraction — overloading is operationally defined as performing a voluntary maximal contraction against unaccustomed resistance.
• progression — progression is how overload is applied gradually over time.
• reversibility-disuse — underloading reverses the threshold gains.
• intensity — intensity (load as % of 1RM) is the variable manipulated to overload.
• exhaustion-set — sets to failure ensure a maximal contraction occurs.
• muscle-hypertrophy — physiological change overload stimulates.