Training is a process of tearing down muscle and building it up again. The adaptations to training require creation of new biological material. During training, additional damage to muscle cells is achieved along with depletion of cellular resources (energy). This is why following training the body is weaker not stronger. However, in order for the body to maintain homeostasis (keep things on an even keel), it initiates not just repair of these cells but also increases them in size and number to reduce the impact of similar future stress. This is known as the General Adaptation Syndrome. In summary, if the stress is too small (intensity or duration) little or no adaptation growth is seen. If the stress is too severe, growth is delayed or even prevented. The ideal training programme would maximally stimulate this General Adaptation to enable the muscular cells to respond to future demands whilst minimizing the stress of the body in order to stimulate the changes.

When we train we choose a specific intensity and duration. Then these are repeated (frequency). In an untrained person significant improvements in exercise capacity are not usually seen until the training intensity exceeds 50% of maximum oxygen uptake.  As we become more trained, this intensity must increase to 70-85% of peak oxygen uptake in order to achieve a positive training response. It should be noted however, that training at this intensity too often results in overtraining, injuries and staleness. Therefore, exercise below this level is important to maintain fitness and allow for active muscular recovery.

In summary - we must regularly stress (overload) the body to achieve a training effect. Too much overload is not beneficial and results in injury and staleness. It is about getting the balance correct.