Repetitive task indicator as a tool for assessment of upper limb musculoskeletal load induced by repetitive task.

A unified repetitive task indicator (RTI) has been proposed, characterizing the upper limb load resulting from repetitive work. Within RTI, the work task is described using parameters which refer to the duration of particular sequences of the work cycle and force exerted, taking into account the posture of the upper limb. On the basis of theoretical and experimental studies, undertaken by the author and on the basis of results of experimental studies conducted in other international research laboratories, available in the literature, an analysis was conducted with the aim of developing and verifying the RTI. A comparison of the RTI with indicators of internal load was performed for eight published study cases. The experimental study cases used for verification purposes were conducted for various variants of load (various types and levels of the external force and duration of cycle periods) and for various physiological indicators of internal load. Strong correlations between RTI and indicators of internal load expressed by the unified indicator (IL), showed considerable credibility of the RTI. Results of the verification are noteworthy, given the wide range of cases examined, differing in terms of the conditions under which they were done, the population examined and internal load indicators used. Thus, this analysis indicates that the proposed RTI reflects well the upper limb load occurring as a result of performing repetitive work.