Psychophysically determined work durations for limiting shoulder girdle fatigue from elevated manual work.
Int J Ind Ergon 1993 Jan; 11(1):19-28
Work durations for limiting shoulder girdle fatigue from elevated manual work were determined using a psychophysical approach. The influence of the rate of repetitive work on fatigue limiting work durations and how it might influence and interact with that of other tasks were of particular interest. Participants were 72 right handed individuals (35 males and 37 females) free of known musculoskeletal problems. Minor anthropometric differences were accommodated. A Baltimore Therapeutic equipment work simulator was used for the repetitive motion task in which the seated subject grasped the tool handle and performed a task consisting of repeated lifting and lowering of the handle, and striking a metal pointer to a metal plate at the end of each excursion. Each cycle consisted of a 180 degree arcing movement to lift the handle, and a similar movement to lower it. Repetition rate was controlled by an electronic timer. Subjects assessed perceived discomfort on the Borg CR-10 scale. A series of four experiments were conducted. Results showed that subjects were able to adjust work trial durations to attain each of three experimentally set levels of perceived arm/shoulder discomfort. Increases in force output requirement from 10 to 20 to 30% maximum voluntary contraction produced significant corresponding decreases in work trial duration. Increases in discomfort led to increasing reductions in work time as a function of force. Average trial durations associated with varying levels of work demand ranged from 29 to 160 seconds. The largest effects on work duration were by rate and force of movement, while reach height and tool weight had comparatively minor impact. Males tended to engage in longer work trials than females. The authors conclude that rate and force of movement are critical to the development of shoulder and arm fatigue, and discuss the possible role of gender related experimental demand characteristics.
Anthropometry; Biomechanics; Cumulative-trauma-disorders; Equipment-design; Ergonomics; Industrial-engineering; Mathematical-models; Musculoskeletal-system-disorders; Occupational-health; Repetitive-work; Sex-factors
International Journal of Industrial Ergonomics