New aspects of the hormone and cytokine response to training

Exercise training is associated with peripheral-cellular and central-cerebral processes, hormonal-neuronal regulation and transmission mechanisms. During the acute training response, peripheral cellular mechanisms are mainly metabolostatic to achieve energy supply and involve associated cytokine and hormonal reactions. Glycogen deficiency is associated with increased expression of local cytokines (interleukin-6, IL-6), decreased expression of glucose transporters, increased cortisol and decreased insulin secretion and β-adrenergic stimulation. A nutrient-sensing signal of adipose tissue may be represented by leptin which, as for insulin, IL-6 and insulin-like growth-factor I (IGF-I), has profound effects on the hypothalamus and is involved in the metabolic hormonal regulation of exercise and training. Muscle damage and repair processes may involve the expression of inflammatory cytokines (e.g. tumour necrosis factor-α, TNF-α) and of stress proteins (e.g. heat shock protein 72). During overreaching and overtraining, a myopathy-like state is observed in skeletal muscle with depressed turnover of contractile proteins (e.g. in fast-type glycolytic fibres with a concomitant increase in slow type myosins). These alterations are influenced by exercise-induced hypercortisolism, and by decreased somatotropic hormones (e.g. IGF-I). The hypothalamus integrates various error signals (metabolic, hormonal, sensory afferents and central stimuli) and therefore pituitary releasing hormones represent the functional status of an athlete and long-term hypothalamic hormonal and sympathoadrenal downregulation are some of the prominent hormonal signs of prolonged overtraining and performance incompetence syndrome.