In addition to a minimum intensity, the training load must be continued for a certain time. High intensity training which is too brief may not allow time for the physical adaptations required by the body. The frequency of training-that is, how often it is carried out-is also important. Training is a stimulus which causes an anabolic adaptation. This adaptation will take time, and so ade quate recovery must be allowed between training sessions for the body tissues to modify themselves. The type of training will dictate will the type of tissue adaptation which occurs, a principle known as the specificity (McCafferty and Horvath, 1977) (see below)