Exercise elicits a multitude of changes in biological functions in the body and could thus be regarded as a stressful stimulus that may disrupt a well-regulated state of homeostasis. In a stress research model, a stressful stimulus is labeled the stressor and the following response is described as the stress reaction (160;193;194).

The stressor-induced reactions are observed in the context of a pre-set and meticulously regulated balance, often referred to as homeostasis in the biological science. As early as 1929, W.B. Cannon described homeostasis as a "coordinated physiological process, which maintains most of the steady states in the organism". Thus, stress may be defined as a disruption of homeostasis (29), and the subsequent reactions are programmed to counterbalance the perturbations of the stressor and to re-establish the homeostatic balance after the stressful stimulus is terminated.