| Work-related musculoskeletal disorders (WMSD) of the upper limb are common among occupational hand transfer tasks. Associated risk factors for WMSD development such as insufficient muscle rest, excessive force, and awkward posture are accentuated by the reduction of cycle time (CT), grip type, and precision requirements as well. Two studies have been conducted to elucidate the effects of CT of a pick-and-place task on muscle activity, grip force, wrist posture, center of pressure, error rate, and perception-based measures (discomfort and difficulty). Placement precision was investigated in the second study.;A CT of less than 5 s led to an unacceptable muscle loading in both pick-and-place studies. Increased precision and weight of the object may increase muscle loading and rest for the muscles we investigated especially for the forearm musculature. (Abstract shortened by UMI.).;The results from the first study suggested that a pace threshold (between 2s and 5 s for this task) is reached at a higher CT than that defined by the ability to perform the task. Similarly, in the second study, static muscle loading exceeded 1% and the muscle rest as determined from a gaps analysis was below 10% for CT ≤ 3s for all muscles. Precision increased loading in ECR, ECU, EDI, and FDS muscles (p<0.001) and increased perceived difficulty (p<0.05). The findings suggest that increased precision increases the loading by 43% in the distal musculature. |
