Power Loading-Induced Fatigue is Influenced by Menstrual Cycle Phase

Purpose 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), mid-follicular (mid FOL), ovulation (OV), and mid-luteal (mid LUT). Methods Sixteen eumenorrheic women performed sessions of maximal explosive leg press (2x10 at 60%1RM 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 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 to OV. Changes in MVC and AL associated (r2 = 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 to 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 to OV. In addition, resting twitch force at mid LUT was lower (p < 0.01) compared to M. Blood lactate levels increased more (p < 0.05) during M compared to mid LUT. Some serum hormone concentrations 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, while mid FOL and mid LUT appear to be superior for acute muscular responses.