Abstract des Autors

Since athletes must push their limits in quest of the minimal differences in performance that separate the champion from the also-ran, overreaching (short-term overtraining) will remain a common part of training. lf overreaching is too great, too monotonous, continued for too long a time, or coupled with too many competitions and nontraining stress factors, an overtraining syndrome rnay result and the athlete's performance may fail to return to expected levels, even if the regeneration is extended. On the basis of available studies, even in top athletes the maximal sustainable duration of overreaching in endurance sports can be assumed to be around three weeks of intensified or prolonged endurance training of more than 3 h/d. The risk of overtraining is increased by (1) one-sided, monotonous training without alternating hard and easy training days, (2) a lack of one complete rest day per week, (3) a high total and increasing training load combined with additional significant nontraining stress factors, and (4) too many competitions. So far as is known at present, physiological responses to overtraining in endurance athletes can be summarized as an inhibition of the transmission of stress (catabolic) signals to target organs such as (1) a decrease in neuromuscular excitability of overloaded muscles, (2) a decrease in adrenoreceptor density (decrease in sensitivity of the organism to catecholamines), (3) a decrease in adrenal sensitivity to ACTH during prolonged overtraining periods (decreased cortisol response) combined with an increased pituitary sensitivity to GHRH (increased GH response) reflecting a shift to a counterregulatory anabolic endocrine responsibility, (4) intracellular protection mechanisms such as an increased synthesis of heat-shock proteins to complement the complex strategy of the organism against overload-related cellular damage, and (5) an additional decrease in sympathetic intrinsic activity in advanced stages that may depend on an elevated concentration of inhibitory neurotransmitters in the brain (so-called central mechanism). The observed overtraining-related decrease in beta-adrenoreceptor density works like the nonselective beta-blockers, resulting in impaired glycogenolysis, glycolysis, lipolysis, heart rate response, and endurance performance ability. Verf.-Referat