The word stress may have a negative connotation but it may also be considered as a stimulus or a challenge, which we have to handle. French scientist Claude Bernard is acknowledged as the first author to recognize that humans, by maintaining internal stability (milieu intérieur), are able to withstand the challenges of the external environment (Bernard 1865). The work of Bernard was refined by Cannon in the early 1920`s, as he described the actions of cells responding to perturbing stimuli in terms of dynamic equilibria, or ``homeostasis" (Cannon 1914). Forty years later, Selye introduced "the general adaptation syndrome" (Selye 1956), where he investigated several internal and external stressors that may disturb the homeostatic balance. Among these stressors was also strenuous exercise. The general adaptation syndrome is made up of three stages: 1) Alarm reaction; the reaction of an organism when it is suddenly exposed to a stressor to which it is not adapted. If the organism can survive, this initial reaction is followed by the adaptation or the `stage of resistance`. 2) Stage of resistance; the organism is fully adapted to the stressor and the symptoms disappear. 3) State of exhaustion; occurs when the adaptation resources of an organism are depleted (Selye 1956). Recently, more interest has risen on the sustained physiological activation leading to increased duration of the stress response (Brosschot et al. 2005). This prolonged stress response may manifest itself in three forms: anticipatory responses to potential stressors, slow recovery from stressors, and/or recurrent activity related to past stressors (Brosschot et al. 2005). (Part of original introduction)
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