Reproducibility of work movements with carpenters' hand tools

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Abstract
To find a model for testing possible new causes of accidents in the construction industry, the degree of precision with which carpenters habitually reproduced familiar work with ordinary hand-tools was investigated Ten experienced carpenters performed standardized sawing, nailing and screwing tasks on two separate days, twice a day. The number of work movements and the time taken for each task were recorded. Perceived exertion was rated according to Borg's scale. The forces used while sawing and screwing were estimated and simulated on a dynamometer with appropriate handles. The activity of seven muscle groups of the work arm and shoulder was recorded with EMG and surface electrodes. Intra-individually the carpenters repeated the standardized work tasks with a high degree of precision (coefficients of variation less than 10%). In the dynamometer simulation, the precision was almost the same in screwing, but not in sawing. The perceived strain was consistently related to three different levels, with screwing rated ‘hardest’ and hammering ‘easiest’. The EMG pattern varied among the ten subjects, but individual patterns and amplitudes were similar at the four trials. Parts of the model described can be used to test whether the reproducibility of movement performance changes after exposure to different work-related strains.