Does Eyelid Squinting Increase Shoulder Muscle Activity?
Work-related musculoskeletal disorders in the neck/shoulder are common problem among computer workers. The physiological mechanisms for development of these disorders, e.g. myalgia and tension neck syndrome, are not yet fully understood. According to the Cinderella hypothesis the low-threshold motor-units are the first ones to be at risk for selective overuse, e.g. causing fibre injuries, in a sustained muscle activation. Hence, a small increase of the “static muscular activity may increase the risk of motor-unit overuse. Visual discomfort has been suggested as one path, among others, that contributes to the generation of MSDs. Interventions including improved lightning have improved visual comfort and reduced rated glare. They have also decreased shoulder pain and showed lower 10th percentile EMG levels in comparison to a control group. Refractive error (blur) and glare that may be reduced by eyelid squint may induce a higher electromyographic (EMG) activity from the orbicularis oculi muscle than a neutral condition. A direct connection between the orbicularis and trapezius muscles, could possibly be a link between visual discomfort and MSDs, and partly explain findings of less shoulder pain after improved lightning conditions. In this study surface electromyography (EMG) was measured from the right orbicularis oculi muscle and bilaterally from the descending trapezius muscle, from 28 subjects. The trapezius EMG was normalised to a submaximal contraction. During the experiment the subjects were asked to squint maximally (Max) for 5 s, at 20％ (80％ open eye area) and 50％ (1 min each), and repeat Max, in intermediate one-minute-periods (Neutral), the subject was asked to look forward. The orbicularis EMG was normalised to the maximal 1-s root-mean-square (RMS) values from the two Max periods. The orbicularis EMG levels increased with instructed squint level. The trapezius levels were low and very similar during the neutral and the squint conditions. The study does not at all support the existence of direct connection between the orbicularis oculi and the trapezius muscles. The question of a possible indirect association, i.e. if a poor visual condition increases both trapezius and orbicularis muscular activity, remains to be focused.
Forsman, M. B(a)nziger, T. Richter, H.O.
Division of Occupational and Environmental Medicine Department of Public Health Sciences Karolinska Centre for Musculoskeletal Research University of G(a)vle, Sweden
国际会议
17th World Congress on Ergonomics(第十七届国际人类工效学大会)
北京
英文
1-5
2009-08-09（万方平台首次上网日期，不代表论文的发表时间）