School of Rehabilitation Science, University of Saskatchewan, Saskatoon, SK, Canada.
Safety and Health Assessment and Research for Prevention Program, Washington State Department of Labor and Industries, Tumwater, WA, USA.
J Biomech. 2021 Jun 23;123:110503. doi: 10.1016/j.jbiomech.2021.110503. Epub 2021 May 7.
Musculoskeletal risk is mediated by body posture, especially for static tasks. Workstations that require non-neutral postures can lead to increased load, muscular fatigue and injury risk. However, demands during simple axial rotation tasks are not well-defined. The purpose of this study is to quantify the muscular activity of during static axial rotation in a range of postures. Eighteen participants performed 76 axial rotation exertions in varying combinations of humeral elevation angles (30°-60°-90°-120°-150°), plane of elevation (30°-60°-90°-120°) and exertion intensity (20-40%). Six unilateral (right) muscles (pectoralis major (clavicular and sternal), posterior deltoid, teres major, infraspinatus, latissiumus dorsi) were monitored using surface electromyography (EMG). EMG was normalized and integrated over 2 s. The influences of elevation, plane, and intensity on activity levels were then tested with a 3-way ANOVAs (p < .05). During internal rotation, activity was highest at low elevation/high plane combinations for the internal rotators, but at high elevation/low plane combinations for the external rotators. During the 40% intensity exertions, activity levels were highest at lower elevations for internal rotator but at high elevations for the external rotators. During external rotation, as the degree of elevation increased, the activity of the external rotator muscles also increased while internal rotators were unaffected. Humeral muscles responsible for axial rotation are influenced by arm posture during axial rotation exertions. High elevation and plane combinations resulted in high demands for external rotator muscles and this should be considered for job design and injury risk.
肌肉骨骼风险受身体姿势影响，尤其是在静态任务中。需要非中立姿势的工作站可能会导致负荷增加、肌肉疲劳和受伤风险。然而，简单轴向旋转任务的要求尚不清楚。本研究的目的是量化在不同姿势下静态轴向旋转过程中的肌肉活动。18 名参与者在不同的肩臂抬高角度（30°-60°-90°-120°-150°）、抬高平面（30°-60°-90°-120°）和施力强度（20%-40%）的组合下进行了 76 次轴向旋转施力。使用表面肌电图（EMG）监测 6 块单侧（右侧）肌肉（胸大肌（锁骨和胸骨）、三角肌后束、大圆肌、冈下肌、背阔肌）。将 EMG 进行归一化和 2 秒积分。然后，使用 3 因素方差分析（p<.05）测试抬高、平面和强度对活动水平的影响。在内部旋转时，对于内部旋转器，在低抬高/高平面组合下活动最高，但对于外部旋转器，在高抬高/低平面组合下活动最高。在 40%强度施力时，内部旋转器的活动水平在较低的抬高高度下最高，但外部旋转器在较高的抬高高度下最高。在外部旋转时，随着抬高角度的增加，外部旋转肌的活动也增加，而内部旋转肌则不受影响。负责轴向旋转的肱骨肌肉在轴向旋转施力时受手臂姿势的影响。高抬高和平面组合导致对外旋肌的高要求，这在工作设计和受伤风险方面应加以考虑。
