Power Loading–Induced Fatigue Is Influenced by Menstrual Cycle Phase

PURPOSE: This study aimed to examine the effects of fatiguing power loading on neuromuscular properties, force production, and metabolic capacities during four phases of the menstrual cycle (MC): menstruation (M), midfollicular (mid FOL), ovulation (OV), and midluteal (mid LUT). METHODS: Sixteen eumenorrheic women performed sessions of maximal explosive leg press (2 × 10 at 60% one-repetition maximum load with 2-min recovery between sets). Serum hormones and neuromuscular responses were measured. RESULTS: The loading protocol significantly decreased power (between −14.2% and −12.5%; P < 0.001) and maximal force production (between maximum voluntary force (MVC); −15.0% and −7.8%; P < 0.001–0.05), while decreasing activation level (between AL; −6.9% and −2.2%; P < 0.001–0.05) in all MC phases. The decreases in AL were greater during mid LUT (P < 0.01) compared with OV. Changes in MVC and AL were associated (r(2) = 0.53; P < 0.01) at all MC phases. The decrease in EMG during MVC did not differ between the MC phases; however, mean power frequency was higher during M (+7.7%; P < 0.05) and mid LUT (+3.1%; P < 0.05) compared with OV (−7.5%). Resting twitch force decreased during mid FOL (−6.9%; P < 0.05) and mid LUT (−16.2%; P < 0.001), and these values were significantly decreased (P < 0.05) compared with OV. In addition, resting twitch force at mid LUT was lower (P < 0.01) compared with M. Blood lactate levels increased more (P < 0.05) during M compared with mid LUT. Some serum hormone concentrations were associated with fatigue-induced changes in neuromuscular properties and force production, but these correlations behaved differently between the MC phases. CONCLUSIONS: OV may offer a more favorable hormonal milieu for acute neural responses, whereas mid FOL and mid LUT seem to be superior for acute muscular responses.