Shoulder postural fatigue and discomfort

Abstract

Does greater strength capacity in the shoulder-complex afford increased protection against regionalized fatigue and discomfort induced by sustained awkward arm postures in light-weight manual assembly environments? This question was addressed by testing the relationship between differences in shoulder complex strength capacity, produced by variations in arm posture within a subject, and among subjects assuming equivalent arm postures, and severity of fatigue and discomfort sensed during a low-exertion manual performance task. Experimental findings showed that: (a) awkward arm postures produced substantial and rapid onset of postural fatigue and discomfort during a light-weight manual performance task where strength demands were low (i.e., less than 15 percent of maximum voluntary contraction (MVC)), (b) variations in strength capability found among arm postures within an individual subject, or among subjects assuming the same arm posture, did not affect onset of substantial fatigue or discomfort when hands are postured near or above shoulder level, and (c) postures which simply appeared to be awkward, or which compromised strength capacity (e.g., working with the arm to the side of the body, or aligned in the coronal plane), did not necessarily increase discomfort of fatigue. Our findings suggest caution against sole reliance upon population or individual worker upper-extremity strength capabilities as predictors of fatigue and discomfort in the shoulder complex when manual exertions are small (e.g., light-weight manual assembly activities involving small parts or small hand-tools) and hands are postured at or above shoulder level. RELEVANCE TO INDUSTRYStronger workers are often selected for manual assembly overhead, or when other awkward upper extremity postures must be sustained. Measurements of subject upper-extremity isometric strength capability in an array of arm postures, and computation of external shoulder load moments, were of no significant value in predicting or gauging onset or severity of fatigue and discomfort experienced in elevated arm postures. Ergonomists are encouraged to eliminate overhead work even in light-weight manual assembly environments and to extend their upper-extremity posture analyses beyond evaluation of anthropometrics, shoulder external load moments, and upper extremity strength capability when specifying arm and shoulder postures in light-weight manual assembly environments,

Prevalence of Musculoskeletal Disorders at Workplaces in the People’s Republic of China

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Influence of paid and unpaid work on psychophysiological stress responses of men and women.

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