Resistance exercise decreases - endorphin immunoreactivity

Previous research investigating the response of plasma P-endorphins (13-EP) to resistance exercise has resulted in equivocal findings. To examine further the effects of resistance exercise on 3-EP immunoreactivity, 10 male and 10 female college-age students participated in a series of controlled isotonic resistance exercises. The session consisted of three sets of eight repetitions at 80% of one repetition maximum (1-RM) for each of the following exercises: (1) bench press; (2) lateral pull-downs; (3) seated arm curls; and (4) military press. Blood plasma was sampled both before and after the lifting routine and P-endorphin levels were determined by radioimmunoassay. A Students t test for paired samples indicated that mean(s.e.) plasma P-endorphin levels after exercise (10.5(1.3) pg R-EP ml-') were significantly decreased as compared with pre-exercise (control) levels (16.5(1.2), P< 0.05). While the mechanism(s) contributing to the decrease in immunoreactivity is unclear, it may be the result of the synergistic effect of R-EP clearance during rest intervals and changes in psychological states between sampling.