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

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 x 1-min all-out efforts with 1-min active recovery. Meals, comprising carbohydrate (CHO) intake of 8 g center dot 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 (similar to 4%, P = 0.020) during SMC and ventilatory inefficiencies during SMC and HIT (similar to 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 (similar to 6% higher blood glucose and similar to 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.