Women Experience Greater Relative But Similar Absolute Neuromuscular Fatigue Than Men During Ramp-incremental Exercise Testing

Sex differences in pulmonary, cardiovascular, or neuromuscular function may affect the decline in neuromuscular performance and the primary mechanism of exercise intolerance. Unlike the cardiopulmonary exercise test (CPET), the musculo-CPET (mCPET) uses brief (5 s) maximal isokinetic power (Piso) measurements at baseline and peak exercise to assess neuromuscular performance and fatigue. PURPOSE: To examine sex differences in neuromuscular performance and fatigue during ramp-incremental (RI) mCPET. We hypothesize men will have greater power (baseline Piso), lower capacity to aerobically support their available muscle power (lower aerobic power index; API), greater reduction in Piso per watt of power achieved (higher fatigue index; FI) than women; both sexes will be limited by neuromuscular performance (no power reserve (PR)) with a similar rate of RI fatigue. METHODS: Participants performed a RI mCPET with and without interleaved Piso measurements every 90 s. Data are presented as mean [SD] and analyzed with two-tailed t-tests or two-way ANOVA. RESULTS: Five men (23 [2] yr; 25 [3] kg/m2; 90 [7] % predicted V̇O2peak) and six women (21 [2] yr; 22 [2] kg/m2; 101 [12] % predicted V̇O2peak) completed both visits. Baseline Piso was greater in men (703 [159] vs 569 [63] W, p = 0.09). API was similar between sexes (40 [4] vs 38 [4] %, p = 0.49). The reduction in Piso per RI-watt was lower in males (FI (0.14 [0.06)] vs 0.26 [0.08] %/W, p = 0.03), but exercise in both sexes was limited by neuromuscular performance (PR: 30 [24] vs 29 [31] % RI-WRpeak, p = 0.97). During interleaved mCPET the rate of fatigue was similar between sexes (main effect of time (F(1.3, 11.9) = 30.5, p < 0.001), no main effect of sex (F(1, 9) = 2.6, p = 0.14), and no interaction (F(3,27) = 1.1, p = 0.35))(Figure). CONCLUSIONS: Despite lower baseline Piso and greater decline in neuromuscular performance per watt in women, the dynamics of the decline with time were similar between the sexes.