Psychophysical studies of repetitive wrist flexion and extension

Abstract

The purpose of this experiment was to investigate the feasibility of using psychophysical methods to determine maximum acceptable forces for various types and frequencies of repetitive wrist motion. Four adjustable work stations were built to simulate repetitive wrist flexion with a power grip, wrist flexion with a pinch grip, and wrist extension with a power grip. The study consisted of two separate experiments. Subjects worked for two days per week during the first experiment, and five days per week during the second experiment. Fifteen women completed the first experiment, working seven hours each day, two days per week, for 20 days. Repetition rates of 2, 5, 10, 15 and 20 motions per minute were used with each flexion and extension task. Maximum acceptable torques were determined for the various motions, grips, and repetition rates without dramatic changes in wrist strength, tactile sensitivity, or number of symptoms. Fourteen different women completed the second experiment, performing a wrist flexion motion (power grip) fifteen times per minute, seven hours per day, five days per week, for 23 days. There were no significant differences in maximum acceptable torque from day to day. However, the average maximum acceptable torque for a five days per week exposure was 36.3% lower than for the same task performed two days per week. Assuming that maximum acceptable torques decrease 36.3% for other repetition rates and motions, tables of maximum acceptable force were developed for female wrist flexion (power grip), female wrist flexion (pinch grip), and female wrist extension (power grip).

Estimating upper limb discomfort level due to intermittent isometric pronation torque with various combinations of elbow angles, forearm rotation angles, force and frequency with upper arm at 90° abduction

“…Snook et al 1995) Similarly the values of elbow angle (45 0 , 90 0 and 135 0 ) with the forearm maintained parallel with the transversal plane were similar to those found in various industrial tasks (Table7).…”

Health hazard evaluation report: HETA-94-0214-2508, MCD, Inc., Anniston, Alabama.

“…30 The force required to perform the wiring jobs was at an unacceptably high level for a female population, according to published psychophysical studies. 38 Performing assembly tasks resulted in awkward postures in several cases (adjusting interlock brackets, for example). Static muscle loading, that is, using a muscle group continuously without sufficient rest periods, was observed with some hand tools.…”

“…38 For a repetition rate of 2 times per minute, the maximum acceptable force for female wrist flexion using a power grip (e.g., pliers) was 3.35 for 90% of the female population, 7.26 lbs. for 50%, and 11.20 lbs.…”

Job stress reactivity and work-related musculoskeletal symptoms

“…A total symptom severity index was calculated for each stress event recorded by summing the intensity rating for pain/soreness and numbness/tingling over all sites. This hand diagram allowed for the rapid assessment of symptom location and severity, and it has been shown to be an adequate indicator of task-related upper extremity symptoms in previous studies Snook, Vaillancourt, Ciriello, & Webster, 1995).…”