Abstract
Six eumenorrheic females (age = 26.3±2.4 yrs; X±SE) exercised until exhaustion (EE;
70% V̇O2max) at the midluteal (LP, 7-8 days after ovulation) and midfollicular (FP, days 7-8)
phases of their menstrual cycles. Phases were confirmed by estradiol and progesterone
concentrations. Each EE test was preceded by a depletion exercise bout (DE; 90 min,
60% V̇O2max and 4 × 1 min, 100% V̇O2max) and 3 days of rest/diet control. Muscle biopsies 1% (vastus lateralis) were taken
post-DE, pre-EE, and post-EE and then analyzed for glycogen content. There was a strong
tendency (P < 0.07) for EE duration to be greater during LP (139.2±14.9 min) than FP (126±17.5
min). Glycogen repletion (pre-EE minus post-DE) following DE was greater (P = 0.05) during the LP than FP (88.2±4.7 vs 72.8±5.7 µmol/g w. w. muscle). However,
EE glycogen utilization (pre-EE minus post-EE/EE time) did not differ between phases
(LP = 0.41±0.08 µmol/g w. w. muscle/min vs FP = 0.33±0.11 µmol/g w. w. muscle/min;
P = 0.17). The results suggest that exercise performance and muscle glycogen content
are enhanced during the LP of the menstrual cycle. These findings imply athletic performance
may be affected by the phases of the menstrual cycle.
Key words
Menstrual cycle - exercise - muscle glycogen
