Abstract Several occupational groups are exposed to periods of low ambient temperatures while performing manual work tasks outdoors. Work tasks typically include heavy lifting, tool handling, and overhead work. This study evaluated the effect of working position and cold environment on muscle activation level (%RMSmax) and fatigue in the upper limb during manual work tasks. Fourteen male participants (25 ± 3 years, 80.9 ± 6.4 kg, 182 ± 5 cm) completed a 2-h test protocol consisting of five test periods alternating with four work periods, wearing identical sets of clothing, under cold (−15 °C) and control (5 °C) conditions. The work periods consisted of manual work at the hip level, manual overhead work, and a lifting exercise. The test periods consisted of isometric maximal voluntary contractions (MVC) and seated rest. Skin temperatures decreased during cold exposure, especially in the extremities. %RMSmax in the forearm was higher in the cold condition both during overhead work and work at the hip level than that for the same work in the control condition, especially at the end of the test when the difference was approximately 25% (equating to 2–3 %RMSmax). For the middle deltoid muscle, the %RMSmax was approximately three times (or 10 %RMSmax) higher during overhead work than work at the hip level, but there was no additional cost of working in the cold. Signs of deltoid muscle fatigue (decrease in electromyography median power frequency and an increase in %RMSmax) were observed during the overhead work periods in both temperature conditions. No decrease in MVC, as a sign of overall muscle fatigue, was observed in either condition. Relevance to industry This study demonstrated that when wearing suitable cold-weather protective clothing, the adverse effect of work posture is much higher than that of cold on muscle demand and physical strain.

中文翻译：

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体力劳动中工作姿势和寒冷环境对上肢肌肉激活水平和疲劳的影响

摘要 一些职业群体在户外执行体力劳动时会暴露在低温环境中。工作任务通常包括搬运重物、工具搬运和高空作业。本研究评估了工作位置和寒冷环境对体力工作任务中上肢肌肉激活水平 (%RMSmax) 和疲劳的影响。14 名男性参与者（25 ± 3 岁，80.9 ± 6.4 公斤，182 ± 5 厘米）完成了一个 2 小时的测试协议，该协议由五个测试周期和四个工作周期交替组成，穿着相同的衣服，在寒冷 (-15 °C) ) 和控制 (5 °C) 条件。工作时间包括髋部的体力劳动、头顶的体力劳动和举重练习。测试期包括等长最大自主收缩 (MVC) 和坐姿休息。在寒冷环境下，皮肤温度会下降，尤其是四肢。在寒冷条件下，前臂的 %RMSmax 在过头工作和髋部水平工作中均高于在控制条件下进行的相同工作，尤其是在测试结束时，差异约为 25%（等于 2 –3 %RMSmax)。对于中三角肌，在过头训练时的 %RMSmax 大约是臀部训练的三倍（或 10%RMSmax），但没有在寒冷中工作的额外成本。在两种温度条件下的头顶工作期间都观察到三角肌疲劳的迹象（肌电图中值功率频率降低和 %RMSmax 增加）。在任何一种情况下，都没有观察到 MVC 减少，这是整体肌肉疲劳的标志。