Stroke Increases Neuromuscular Fatigability in Females but not Males During Isometric Exercise

Purpose: Females have worse motor-related functional outcomes than males post stroke. However, it is unclear whether stroke affects motor performance such as neuromuscular fatigability differently between sexes. This study determined sex differences in the impact of stroke on fatigability. Methods: Forty-one chronic stroke survivors (23 female, ≥6 months post stroke) and 23 age-matched neurotypical controls (12 female) performed a sustained submaximal (30% of maximum) isometric knee extension contraction with paretic or dominant leg, respectively. Task duration was used to quantify fatigability. Potentiated twitch (Q tw ) and surface electromyography (EMG) were assessed to quantify muscle contractile properties and neuromuscular activation, respectively. Separate two-way ANOVAs were performed to determine main and interaction effects of group and sex on fatigability and neuromuscular measurements. Separate Pearson correlations were performed to explore associations between fatigability and neuromuscular measurements. Results: There was an interaction effect of group and sex on task duration where female stroke survivors had a shorter task duration than neurotypical females (254 ± 121 vs. 445 ± 228 s, p < 0.001) whereas this difference was not observed between male stroke survivors (248 ± 132 s) and neurotypical males (260 ± 72 s, p = 0.628). Also, neurotypical females had a longer task duration than neurotypical males ( p = 0.009); however, there were no differences in task duration between male and female stroke survivors ( p = 0.839). Stroke survivors had a shorter task duration than neurotypical controls (251 ± 124 vs. 356 ± 193 s, p = 0.008). Males had a shorter task duration than females (253 ± 112 vs. 319 ± 186 s, p = 0.027). Stroke survivors had less of a change in Q tw (35 ± 16 vs. 51 ± 13% reduction, p < 0.001) and EMG (35 ± 28 vs. 98 ± 41% increase, p < 0.001) than neurotypical controls during exercise. Females had less of a change in Q tw (36 ± 14 vs. 46 ± 18% reduction, p = 0.020) and EMG (47 ± 39 vs. 67 ± 49% increase, p = 0.021) than males during exercise. Within the stroke survivor group, a shorter task duration was associated with less Q tw reduction for female stroke survivors ( r = 0.656, p = 0.001), but a shorter task duration was associated with greater Q tw reduction for male stroke survivors ( r = -0.519, p = 0.039). Conclusions: Stroke increased fatigability in females but not males during sustained submaximal isometric knee extension exercise. This sex-specific impact of stroke on fatigability is likely due to central versus peripheral mechanisms.