INFLUENCE OF MENSTRUAL STATUS ON FLUID REPLACEMENT AFTER EXERCISE-INDUCED DEHYDRATION IN HEALTHY-YOUNG WOMEN

Objective-To determine whether fluid replacement after exercise induce d dehydration varies over the normal menstrual cycle. Methods-Five sub jects, with a regular menstrual cycle lasting 28(SEM 2) d, were dehydr ated by 1.8(0.1)% of their preexercise mass by cycle exercise in the h eat, Trials were undertaken 2 d before (trial -2) and 5 and 19 d after the onset of menses (trials 6 and 20 respectively). After exercise, s ubjects ingested a fixed volume, equivalent to 150% of mass loss, of a commercially available sports drink over a 60 min period. Results-Cum ulative urine output [median(range)] over the 6 h following ingestion was the same on all trials: 714(469-750) ml on trial -2; 476(433-639) ml on trial 6; 534(195-852) ml on trial 20. There was no menstrual cyc le effect on urinary electrolyte (Na+, K+, Cl-) excretion or serum ele ctrolyte (Na+, K+, Cl-) concentrations. Plasma volume increased by 8-1 2% of the postexercise value following rehydration. The percentage of ingested fluid retained did not differ between trials at any time, Six hours after drink ingestion, net fluid balance was not different from the initial value on any of the trials. Conclusions-Acute replacement of exercise induced fluid losses is not affected by the normal menstr ual cycle.