Women report more work-related pain and neck/shoulder musculoskeletal disorders than men. For the same absolute workload, due to lower strength, females generally work at a higher relative intensity, which could induce more fatigue. However, the arm’s anthropometric load (AL) of men is higher. Therefore, simply lifting their arm could be more fatiguing. Sex as a variable is formed of many constructs, and analyses can become muddied by their differing responses to fatigue. No studies have considered AL, when comparing how fatigue affects men and women. The purpose was to determine if including the arm’s AL in the statistical analysis would impact findings of sex-specific effects of shoulder fatigue on muscle EMG. Fifty-five (29m/26f) participants completed a repetitive pointing task (RPT) at shoulder height until they reported fatigue of 8+ on the BORG CR-10 scale. Muscle activities were measured using surface electrodes placed over the anterior deltoid (AD) and upper trapezius (UT) muscles. Muscle activity amplitude was quantified using root mean square (RMS). First- and last-minute data were used to assess change from no-fatigue (NF) to fatigue-terminal (FT) conditions. AL was calculated using sex-specific body parameter equations. General estimating equations (GEE) were used to determine the effects of sex and fatigue on RMS values, while including AL in the GEE. There was no sex difference in time to reach fatigue. A significant main effect of sex on RMS was observed (χ2(1) = 4.17, p = 0.04) when including AL as a covariate. Females displayed a significantly higher percentage change in AD RMS from NF to FT, compared to males (p = 0.03), when AL was included in the GEE. No sex differences in UT were observed. This sex difference emerged when AL was included as a covariate, suggesting that sex-associated anthropometric differences may contribute to sex differences in the fatigue response. Differences in the impact of AL on AD compared to UT could be explained by differences in their respective mechanical roles or muscle fiber content. Anthropometrics may be useful to include as covariates in future research to separate individual anthropometric differences from sex differences.

中文翻译：

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性是上肢重复运动任务中机械变量的代表吗？性别和人体测量负荷对肌肉疲劳影响的研究

与男性相比，女性报告更多与工作相关的疼痛和颈部/肩部肌肉骨骼疾病。对于相同的绝对工作量，由于强度较低，女性通常以较高的相对强度工作，这可能会导致更多的疲劳。然而，男性手臂的人体测量负荷 (AL) 更高。因此，简单地抬起他们的手臂可能会更疲劳。性别作为一个变量由许多结构组成，分析可能会因它们对疲劳的不同反应而变得混乱。在比较疲劳对男性和女性的影响时，没有研究考虑过 AL。目的是确定在统计分析中包括手臂的 AL 是否会影响肩部疲劳对肌肉 EMG 的性别特异性影响的发现。五十五名 (29m/26f) 参与者在肩高处完成了重复指向任务 (RPT)，直到他们在 BORG CR-10 量表上报告疲劳 8+。使用放置在前三角肌 (AD) 和上斜方肌 (UT) 上的表面电极测量肌肉活动。使用均方根 (RMS) 量化肌肉活动幅度。第一分钟和最后一分钟的数据用于评估从无疲劳 (NF) 到疲劳终端 (FT) 条件的变化。AL 是使用特定性别的身体参数方程计算的。一般估计方程 (GEE) 用于确定性别和疲劳对 RMS 值的影响，同时将 AL 包括在 GEE 中。达到疲劳的时间没有性别差异。当将 AL 作为协变量时，观察到性别对 RMS 的显着主要影响（χ2(1) = 4.17，p = 0.04）。当 AL 包含在 GEE 中时，与男性相比，女性从 NF 到 FT 的 AD RMS 变化百分比显着更高（p = 0.03）。未观察到 UT 的性别差异。当 AL 作为协变量时出现这种性别差异，这表明与性别相关的人体测量差异可能导致疲劳反应中的性别差异。与 UT 相比，AL 对 AD 影响的差异可以通过它们各自的机械作用或肌纤维含量的差异来解释。人体测量学可能有助于在未来的研究中作为协变量将个体人体测量学差异与性别差异分开。当 AL 作为协变量时出现这种性别差异，这表明与性别相关的人体测量差异可能导致疲劳反应中的性别差异。与 UT 相比，AL 对 AD 影响的差异可以通过它们各自的机械作用或肌纤维含量的差异来解释。人体测量学可能有助于在未来的研究中作为协变量将个体人体测量学差异与性别差异分开。当 AL 作为协变量时出现这种性别差异，这表明与性别相关的人体测量差异可能导致疲劳反应中的性别差异。与 UT 相比，AL 对 AD 影响的差异可以通过它们各自的机械作用或肌纤维含量的差异来解释。人体测量学可能有助于在未来的研究中作为协变量将个体人体测量学差异与性别差异分开。