Impact Of Menstrual Cycle On Submaximal Exercise Vo2 And Critical Power In Active Eumenorrheic Females

PURPOSE: The effects of the menstrual cycle (MC) on exercise metabolism and performance are equivocal. The purpose of this study was to investigate whether the MC impacted submaximal exercise oxygen consumption (VO2) and Critical Power (CP) in recreationally active, eumenorrheic females. METHODS: Eight eumenorrheic females (Age: 33 ± 8 y, VO2max: 36.9 ± 3.8 ml/kg/min) completed fasted exercise testing in 3 distinct phases of the MC (early follicular, late follicular, and mid luteal). MC phase was determined using calendar-based counting, ovulation test strips, and confirmed via serum hormones (estrogen and progesterone). For submaximal exercise, participants cycled for 20 min at 50% VO2max while VO2 and respiratory exchange ratio (RER) were measured with indirect calorimetry. Rating of perceived exertion (RPE) was measured with Borg 6-20 Scale. After submaximal exercise, participants rested for 10 min and performed a 3-min all-out test to assess CP. Power output (W) was continuously measured to determine CP, which was defined as mean W in final 30 sec of 3-min all-out test. Repeated measures ANOVA was used to assess differences in submaximal responses for VO2 and RER, and 3-min all-out CP. Friedman tests were used to assess differences in RPE. RESULTS: For submaximal cycling, VO2 did not differ across MC (early follicular: 1.27 ± 0.22 L/min, late follicular: 1.27 ± 0.20 L/min, mid-luteal: 1.27 ± 0.22 L/min; p-value = 0.98; effect size = 0.01). However, RER was higher during late follicular (0.91 ± 0.03) than early follicular (0.89 ± 0.05) and mid-luteal (0.89 ± 0.03) phases (p = 0.12; effect size = 0.30). RPE was lower during late follicular (11 ± 2) compared to early follicular (13 ± 2) and mid luteal (13 ± 2)(p = 0.04). For the 3-min all-out test, CP did not differ by MC phase (early follicular: 138 ± 31 W, late follicular: 136 ± 33 W, mid luteal: 136 ± 31 W; p = 0.52; effect size = 0.07). CONCLUSIONS: These preliminary results in 8 recreationally active, eumenorrheic females suggest that submaximal exercise VO2 and CP do not differ across the MC, despite minor differences in submaximal substrate utilization and perceived exertion. Texas Woman's University ORSP Small Grant