Fatigue Resistance Is Altered during the High-Hormone Phase of Eumenorrheic Females but Not Oral Contraceptive Users

Abstract

ABSTRACT Purpose This study aimed to examine the effect of ovarian hormones and their synthetic equivalents on substrate utilization and fatigue resistance during a race-specific cycling protocol. Methods Seventeen well-trained female cyclists (nine eumenorrheic females, eight oral contraceptive users) completed two experimental trials, in a randomized order, in their low- (follicular/sugar pill) and high-hormone (luteal/active pill) phases. Each 91-min trial consisted of a 45-min moderate-intensity component (submaximal cycling, or SMC) followed by 6 min of high-intensity (HIT) and then a fatigue resistance test (FRT): 6 × 1-min all-out efforts with 1-min active recovery. Meals, comprising carbohydrate (CHO) intake of 8 g·kg−1 body mass, were standardized 24-h pretrial. An electrolyte-only solution was provided ad libitum during each trial. Results In eumenorrheic females, a large reduction in average power during FRT was observed in the luteal phase (277 ± 31 vs 287 ± 33 W; P = 0.032). Greater CHOox (~ 4%, P = 0.020) during SMC and ventilatory inefficiencies during SMC and HIT (~7%, P < 0.001) were also observed in the luteal phase. In contraceptive users, despite some phasal changes in cardiorespiratory and metabolic data in SMC (~6% higher blood glucose and ~2% higher minute ventilation in active pill phase), none of the performance parameters in the FRT were different. Conclusions Fatigue resistance was compromised only in high-hormone phase of the menstrual cycle, with eumenorrheic females likely susceptible because of increased CHO utilization during SMC. Hormone-induced ventilatory inefficiencies may also have increased metabolic demand. These findings emphasize the need to maintain CHO availability for power production, particularly in high-hormone phases.