Quantifying exposure in occupational manual tasks with cumulative trauma disorder potential

A method of describing the musculoskeletal loads in the hand and wrist during manual tasks is presented. A profile of twelve factors is used to quantify the exposure of applicable soft tissues to modes of loading suggested as being related to a number of chronic, work-related musculoskeletal disorders such as chronic muscle strain, tenosynovitis, and carpal tunnel syndrome. These factors include estimates of tendon loads and movement, frictional work done on the tendon sheaths, and muscle activation determined using electromyography. The response of these measures to changes of force, repetition, and posture was studied using eight conditions of a simulated task utilizing a pistol grip tool. Measures of tendon frictional work and dynamic electromyographic activity best paralleled the injury outcomes of an epidemiological study using similar task definitions (Silverstein et al. 1986). This field-usable system is being used currently to investigate the relationship between occupational exposure and musculoskeletal disorders.