Temporal dependence of trapezius muscle activation during sustained eye-lens accommodation at near

Abstract

In this experimental study different levels of oculomotor load were induced via optical trial lenses. The aim was to investigate the temporal dependence of a moderate visual load on trapezius muscle activity. Trapezius muscle activity was measured with bipolar surface electromyography (EMG). Sixty-six subjects with a median age of 36 (range 19-47, std 8) viewed a black and white Gabor grating (5 c/deg) through 0 D, and -3.5 D lenses, in periods of 7-min. An auto refractor was used to continuously sample data on eye-lens accommodation during the vision tasks. Response-diopters were used as a dichotomous high/low accommodation grouping variable. For these groups EMG amplitudes during minutes 1-7 per each lens trial were studied separately with Generalized Estimating Equations (GEE). The analysis results showed significant increases in trapezius muscle activity over time for both viewing conditions. For the binocular -3.5 D condition response-diopters gave a significant positive contribution to the EMG amplitude. The results indicate that sustained eye-lens accommodation at near, during ergonomically unfavorable viewing conditions, may increase the risk for trapezius muscle myalgia. © 2013 Springer-Verlag.