Physiologists define stress as how the body reacts to a stressor, a stimulus that causes stress. Acute stressors affect an organism in the short term; chronic stressors over the longer term.
Alarm is the first stage, which is divided into two phases: the shock phase and the anti-shock phase.
· Shock phase: During this phase, the body can endure the stressor effect. The organism's resistance to the stressor drops temporarily below the normal range and some level of shock may be experienced.
· Anti-shock phase: When the threat or stressor is identified or realized, the body starts to respond and is in a state of alarm. During this stage, the locus coeruleus/sympathetic nervous system is activated and catecholamines such as adrenaline are being produced, hence the fight-or-flight response. The result is: increased muscular tonus, increased blood pressure due to peripheral vasoconstriction and tachycardia, and increased glucose in blood. There is also some activation of the HPA axis, producing glucocorticoids (cortisol, aka the S-hormone or stress-hormone).
Resistance is the second stage.
Increased secretion of glucocorticoids plays a major role, intensifying the systemic response—they have lypolytic, catabolic and anti-anabolic effects: increased glucose, fat and aminoacid/protein concentration in blood. Moreover, they cause lymphocytopenia, eosinopenia, neutrophilia and polycythemia. In high doses, cortisol begins to act as a mineralocorticoid (aldosterone) and brings the body to a state similar to hyperaldosteronism. If the stressor persists, it becomes necessary to attempt some means of coping with the stress. Although the body begins to try to adapt to the strains or demands of the environment, the body cannot keep this up indefinitely, so its resources are gradually depleted.
Exhaustion or Recovery will define the third stage.
Recovery stage follows when the system's compensation mechanisms have successfully overcome the stressor effect (or have completely eliminated the factor which caused the stress). The high glucose, fat and aminoacid levels in blood prove useful for anabolic reactions, restoration of homeostasis and regeneration of cells.
· Exhaustion is the alternative third stage in the GAS model. At this point, all of the body's resources are eventually depleted and the body is unable to maintain normal function. The initial autonomic nervous system symptoms may reappear (sweating, raised heart rate, etc.). If stage three is extended, long-term damage may result (prolonged vasoconstriction results in ischemia which in turn leads to cell necrosis), as the body's immune system becomes exhausted, and bodily functions become impaired, resulting in de-compensation.
Relevance to athletes:
The above thumb nail sketch of stress response is (or should be) the framework of all training protocol and workout design!
Read, ReRead and think………….