Despite ample evidence that females are weaker and possess smaller muscle cross-sectional areas (CSAs) compared to males, it remains unclear if there are sex-related differences in the properties of motor units (MU). Eleven males (age 22 ± 3 years) and 12 females (age 21 ± 1 years) performed isometric trapezoid muscle actions at 10% and 70% of maximal voluntary contraction (MVC). Surface electromyography signals were recorded and decomposed into MU action potential (AP) waveforms and firing instances. Average MUAP amplitudes (MUAPAMPS), mean firing rates (MFRs), initial firing rates (IFRs), and recruitment thresholds (RT) were calculated for the 10% MVC, while MUAPAMPS, IFRs, and MFRs were regressed against RT for the 70% MVC. Ultrasonography was used to measure CSA of the first dorsal interosseous (FDI). Males had greater CSAs (p < 0.001; males 2.34 ± 0.28 cm2, females 1.82 ± 0.18 cm2) and MVC strength (p < 0.001; males 25.9 ± 5.5 N, females 16.44 ± 2.5 N). No differences existed for MUAPAMPS, IFRs, MFRs, or RTs (p > 0.05) during the 10% MVC. For the 70% MVC, the y-intercepts from the MUAPAMPS vs. RT relationships were greater (p < 0.05) for the males (males - 0.19 ± 0.53 mV; females - 0.78 ± 0.75 mV), while the inverse was true for the MFR vs. RT relationships (males 31.55 ± 6.92 pps, females 38.65 ± 6.71 pps) with no differences (p > 0.05) in the slopes. Therefore, smaller CSAs and weaker MVCs are likely the result of smaller higher-threshold MUs for females.

中文翻译：

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在高强度但不是低强度的收缩过程中，与性别相关的第一背骨间运动单位放电速率和动作电位振幅的差异。

尽管有充分的证据表明，与男性相比，女性较弱并且具有较小的肌肉截面积（CSA），但尚不清楚运动单位（MU）的特性是否存在性别相关的差异。11名男性（22±3岁）和12名女性（21±1岁）以最大自愿收缩（MVC）的10％和70％进行了等距梯形肌肉动作。记录表面肌电信号并将其分解为MU动作电位（AP）波形和触发实例。计算10％MVC的平均MUAP振幅（MUAPAMPS），平均放电率（MFR），初始放电率（IFR）和募集阈值（RT），而将MUAPAMPS，IFR和MFR相对于RT回归70％ MVC。超声用于测量第一背骨间（FDI）的CSA。男性具有更大的CSA（p <0.001; 男性2.34±0.28 cm2，女性1.82±0.18 cm2）和MVC强度（p <0.001；男性25.9±5.5 N，女性16.44±2.5 N）。在10％MVC期间，MUAPAMPS，IFR，MFR或RT没有差异（p> 0.05）。对于70％的MVC，男性（男性-0.19±0.53 mV；女性-0.78±0.75 mV）的MUAPAMPS与RT关系的y截距更大（p <0.05），而反之则成立MFR与RT的关系（男性31.55±6.92 pps，女性38.65±6.71 pps）在斜率上无差异（p> 0.05）。因此，较小的CSA和较弱的MVC可能是女性较小的较高阈值MU的结果。对于70％的MVC，男性（男性-0.19±0.53 mV；女性-0.78±0.75 mV）的MUAPAMPS与RT关系的y截距更大（p <0.05），而反之则成立MFR与RT的关系（男性31.55±6.92 pps，女性38.65±6.71 pps）在斜率上无差异（p> 0.05）。因此，较小的CSA和较弱的MVC可能是女性较小的较高阈值MU的结果。对于70％的MVC，男性（男性-0.19±0.53 mV；女性-0.78±0.75 mV）的MUAPAMPS与RT关系的y截距更大（p <0.05），而反之则成立MFR与RT的关系（男性31.55±6.92 pps，女性38.65±6.71 pps）在斜率上无差异（p> 0.05）。因此，较小的CSA和较弱的MVC可能是女性较小的较高阈值MU的结果。