Response of beta-endorphin and estradiol to resistance exercise in females during energy balance and energy restriction.

The acute effect of weightlifting on beta-endorphin and estradiol was studied in experienced female recreational weightlifters. Five eumenorrheic females completed two months of testing, each with a different sequence of testing conditions (SEQ1 and SEQ2). In SEQ1, a week of weight maintenance diet and prescribed exercise (3 d.wk-1, 3 sets, approximately 85% 1 RM, 10-12 reps, eight lifts) beginning on d 11 of their menstrual cycle was followed by measurement of hormone response to a weightlifting bout during energy balance (EBAL) on d 18. This included blood sampling via a catheter before, just after, and at 15 and 30 min of recovery. The women consumed 500 kcal per day for the next 48 hrs and then repeated the weightlifting test during negative energy balance (NEBAL). SEQ2 was similar except that the 48 hrs of NEBAL preceded the EBAL test condition. Estradiol and beta-endorphin increased from baseline to immediately post exercise under both dietary conditions but was significant only during NEBAL. Estradiol increased 1.6 fold and beta-endorphin 3.7 fold by the end of the resistance exercise bout during NEBAL. Both hormones were also elevated for a longer time during recovery in the NEBAL condition. Since estradiol and beta-endorphin can suppress gonadotropin release, it is possible that repeated elevations in these hormones during weightlifting, especially concurrent with energy restriction, could contribute to disruption of the menstrual cycle.