Applied Physiology, Nutrition, and Metabolism, Ahead of Print.
Data are scant on sex-related differences for electrically evoked contractions, which assess intrinsic contractile properties while limiting spinal and supraspinal adaptations to mitigate fatigue. Furthermore, the few studies that exist use stimulus frequencies considerably higher than the natural motor unit discharge rate for the target force. The purpose of this study was to compare force loss to electrically evoked contractions at a physiological stimulus frequency among young females (n = 12), young males (n = 12), old females (n = 11), and old males (n = 11). The quadriceps of the dominant leg were fatigued by 3 min of intermittent transcutaneous muscle belly stimulation (15 Hz stimulus train to initially evoke 25% of maximal voluntary force). Impairment of tetanic contractile impulse (area under the curve) did not differ between sexes for young or old adults or between age groups, with a pooled value of 55.2% ± 12.4% control at the end of fatigue. These data contrast with previous findings at 30 Hz, when the quadriceps of females had greater fatigue resistance than males for young and old adults. The present results highlight the impact stimulus frequency has on intrinsic fatigability of muscle; the findings have implications for future fatigue paradigms and treatment approaches when utilizing electrical stimulation for rehabilitation. Novelty Fatigue was not different between sexes with a stimulation frequency comparable to discharge rates during voluntary contractions. These results highlight that stimulus frequency not only influences fatigue development but also between-group differences.

中文翻译：

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膝伸肌的电诱发力损失对于年轻和年老的女性和男性来说是等效的。

应用生理学、营养学和代谢，提前出版。
关于电诱发收缩的性别相关差异的数据很少，这些差异评估内在收缩特性，同时限制脊柱和脊柱上的适应以减轻疲劳。此外，现有的少数研究使用的刺激频率远高于目标力的自然运动单位放电率。本研究的目的是在年轻女性 (n = 12)、年轻男性 (n = 12)、老年女性 (n = 11) 和老年男性 (n = 11)。优势腿的股四头肌因 3 分钟的间歇性经皮肌肉腹部刺激（15 Hz 刺激训练以最初唤起 25% 的最大随意力）而疲劳。强直收缩冲动的损害（曲线下面积）在年轻人或老年人之间或年龄组之间没有差异，在疲劳结束时控制的汇总值为 55.2% ± 12.4%。这些数据与之前在 30 Hz 时的发现形成对比，当时女性的股四头肌在年轻人和老年人中比男性具有更高的抗疲劳性。目前的结果突出了刺激频率对肌肉内在疲劳的影响；当利用电刺激进行康复时，这些发现对未来的疲劳范式和治疗方法有影响。新奇疲劳在两性之间没有差异，其刺激频率与自主收缩期间的放电率相当。