Sex Differences in Motor Unit Discharge Rates at Maximal and Submaximal Levels of Force Output

J Greig Inglis, David A. Gabriel
2020 Applied Physiology, Nutrition and Metabolism  
This study evaluated potential sex differences in motor unit (MU) behaviour at maximal and submaximal force outputs. Forty-eight, 24 females and 24 males, performed isometric dorsiflexion contractions at 20, 40, 60, 80, and 100% of a maximum voluntary contraction (MVC). Tibialis anterior electromyography was recorded both by surface and intramuscular electrodes. Compared to males, females had a greater MU discharge rate (MUDR) averaged across all submaximal intensities (Δ 0.45 pps, 2.56%).
more » ... exhibited greater increases in MUDR above 40% MVC, surpassing females at 100% MVC (p's<0.01). Averaged across all force outputs, females had a greater incidence of doublet and rapid discharges and a greater percentage of MU trains with doublet and rapid (5-10ms) discharges (Δ 75.55% and 61.48% respectively, p's<0.01). A sub-set of males (n=8) and females (n=8), matched for maximum force output, revealed that females had even greater MUDR (Δ 1.38 pps, 7.47%) and percentage of MU trains with doublet and rapid discharges (Δ 51.62%, 56.68% respectively, p's<0.01) compared to males at each force output, including 100% MVC. Analysis of the sub-set of strength matched males and females suggest that sex differences in MU behaviour may be a result of females needing to generate greater neural drive to achieve fused tetanus. Novelty bullets: • Females had higher MUDRs, and greater percentage of motor unit trains with doublets across submax force outputs (20-80%MVC). • Differences were even greater for a strength matched sub-set. • Differences in motor unit behaviour may arise from musculoskeletal differences requiring greater neural drive in females.
doi:10.1139/apnm-2019-0958 pmid:32338038 fatcat:guar3mepqbe3vdn7gpsbhelrfa