Der Schmerz
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A series of studies with humans as well as experiments carried out on animals have shown that physical exercise leads to temporary hypoalgesia. Reduced sensitivity to pain is not only demonstrable after long-distance exercise (such as a marathon run) but also during and after intensive physical exercise on a laboratory ergometer. In a double blind study (20 mg naloxone versus placebo) experimental pain thresholds (electrical intracutaneous finger and dental pulp stimulation) and plasma hormone levels (beta-endorphin, cortisol, and catecholamines) were measured in ten healthy athletic men before, during, and after physical exercise on a cycle ergometer. ⋯ Central pain inhibitory systems are probably thereby activated by the stimulation of afferent nerves endings (group III and IV) in the skeletal muscle. The same trigger mechanism also plays a role as a release stimulus for hormones which are secreted in increased measure during physical exercise (catecholamines, pituitary hormones). Plasma beta-endorphin is probably not directly involved in the exercise-induced hypoalgesia but is rather a "marker" for the activating of central analgesia mechanisms.