Gender effect on beta-endorphin response to exercise

Purpose: Twelve healthy men (26.4 yr) and women (26.8 yr) were compared at rest and after cycling for 25 min at 60 and 80% (V) over dot O-2max to dete rmine whether gender and menstrual cycle influenced circulating beta-endorp hin concentration (BE). Methods: (V) over dot O-2max was determined on a cy cle ergometer, and subjects completed the exercise in a randomized order. W omen were tested in both the luteal (L) and follicular (F) phases of their menstrual cycle, which was confirmed by their blood estrogen levels. All te sts were conducted in the morning after a 30-min rest (12-h postabsorptive) . An indwelling venous catheter placed in a forearm vein enabled blood samp ling at rest, 25 min of cycling, and 25 min of recovery. Results: Resting B E was similar for men before both 60 and 80% intensities of exercise, 5.27 +/- 0.43 and 5.30 +/- 0.33 pmol.ml(-1), respectively. BE was not significan tly changed at 60% (V) over dot O-2max (6.54 +/- 0.33 pmol.mL(-1)) but sign ificantly increased at 80% (V) over dot O-2max (11.90 +/- 1.98 pmol.mL(-1)) . Women tended to have slightly lower BE during the L compared with F, but this did not reach significance (L = 4.40 +/- 0.22, F = 4.73 +/- 0.30 pmol. mL(-1)). Cycling at 60% (V) over dot O-2max did not significantly increase BE in the L (5.41 +/- 0.42 pmol.mL(-1)) nor the F (5.35 +/- 0.40 pmol.mL(-1 )). Cycling at 80% (V) over dot O-2max increased BE to a similar extent in both the L and F phase, respectively (10.44 and 10.96). Although the BE con centrations tended to be slightly lower in women compared with men at 80% ( V) over dot O-2max this did not reach statistical significance. Conclusions : These data suggest that women cycling at 80% (V) over dot O-2max will hav e a similar BE response to men independent of their menstrual cycle. BE in women at rest and who exercise at lower exercise intensities may have sligh tly lower BE levels then men independent of the time of the women's menstru al cycle.