Shoulder-arm muscular activity and reproducibility in carpenters' work

The purpose of the present study was to analyse the levels of muscle activity that experienced carpenters reach in some arm-shoulder muscles when performing familiar tasks, and to find whether there are intra- and inter-individual similarities in muscle activity. Ten healthy carpenters performed twice on the same day: their tasks were, manual screwdriving at eye level, manual sawing on a saw horse, and nailing upward into the ceiling. Two weeks later the experiment was repeated. Normalized electromyography was used. The median activity levels during the period analysed did not exceed 15% of maximum electromyographic activity for any of the muscle groups studied. For some muscles and activities there were wide ranges of median activity levels. The most activated muscles in all three tasks were the trapezius pars descendens, infraspinatus and anterior deltoid. There was an intra-individual similarity between the median values from each trial.