Wrist discomfort levels for combined movements at constant force and repetition rate

Sixteen male subjects each performed a repetitive, downwards, non-prehensile wrist exertion task with the arm pronated, at a rate of 15 times per minute and with a force of 10N ± 1N in 49 combinations of flexion/extension and radial/ulnar deviation to 0%, 18%, 38% and 55% of the Range of Motion (ROM) for 5 min each. The dependent measure was discomfort measured on a 100 mm visual analogue scale and for most of the analyses these were standardized by using the min - max procedure of Gescheider (1988) . These Standardised Discomfort Levels (SDLs) were fitted to mathematical equations from which iso-discomfort contours were derived relative to the percentages of flexion/extension and radial/ulnar-deviation ROM used. The lowest standardized discomfort was found for the neutral wrist posture, followed by 18% extension with neutral radial/ulmar deviation. The results reveal interesting features of the processes involved and provide useful avenues for further research.