Abstract

Plasmatic levels of beta-endorphin during maximal graded bicycle stress test were measured by RIA on extracted plasma in 10 well-trained (A group) and in 8 untrained subjects (C group). Blood samples were obtained at rest, at peak work load and at the third, 10th and 90th min of revovery. For every stress test the following were evaluated exercise time, maximum work load, total work load, maximum double product and mean K (an index of velocity of heart rate recovery during the first three minutes after the exercise). Both groups A and C showed a significant rise in beta-endorphin activity at the third minute of recovery; the increase was significantly greater in trained rather than in sedentary subjects (p<0.01). Beta-endorphin release was closely related to mean K; no relationship was found between exercise time, maximum work load, total work load, maximum double product and beta-endorphin rise. Our data shows that a release of beta-endorphin occurs during the initial phase of recovery after a maximal stress test; beta-endorphin rise is greater in trained subjects and correlates with the speed of heart rate recovery, but has no relationship with the duration and the grade of the effort. Whether beta-endorphin increase plays a role in the rapid decrease of adrenergic tone which occurs after exercise or represents a secondary phenomenon remains to be determined. Verf.-Referat