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

Abstract

To examine the effect of ovarian hormones and their synthetic equivalents on substrate utilisation and fatigue resistance during a race-specific cycling protocol. 17 well-trained female cyclists (9 eumenorrheic females, 8 oral contraceptive users), completed two experimental trials, in a randomised 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 (SMC) followed by 6-min of high-intensity (HIT) and then a fatigue resistance test (FRT): 6x1-min all-out efforts with 1-min active recovery. Meals, comprising carbohydrate (CHO) intake of 8 g.kg-1 body mass, were standardised 24-h pre-trial. An electrolyte-only solution was provided ad-libitum during each trial. 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 OC 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. Fatigue resistance was compromised only in high-hormone phase of the menstrual cycle, with eumenorrheic females likely susceptible due to increased CHO utilisation during SMC. Hormone-induced ventilatory inefficiencies may also have increased metabolic demand. These findings emphasise the need to maintain CHO availability for power production, particularly in high-hormone phases.