Interobserver repeatability and validity of an observation method to assess physical loads imposed on the upper extremities

Interobserver repeatability and validity were assessed for a new semiquanti tative, time-based observation method for the estimation of physical loads imposed on the upper extremities. Six risk factors of upper extremity disor ders were included in the method: repetitive use of hand, use of hand force , pinch grip, non-neutral wrist posture, elevation of upper arm, local mech anical pressure. Two occupational health nurses were trained to use the met hod. They observed 127 work cycles at a food-processing plant and a paper m ill. The method was validated against expert observations from the video, c ontinuous recordings of myoelectric activity (EMG) of forearm muscles, and wrist posture measured with goniometers. Interobserver repeatability was go od or moderate for repetitive use of hand, hand force, pinch grip (range ka ppa = 0.58-0.71 on the right; 0.60-0.61 on the left side). Interobserver re peatability was moderate or poor for non-neutral wrist posture, elevation o f the upper arm and local mechanical pressure. Validity ranged from moderat e to good for repetitive use of hand, use of hand force, pinch grip and non -neutral wrist posture when expert observation was used as reference standa rd. When observations were validated against force estimations (EMG) and wr ist goniometer data, validity was poor. In the absence of generally accepte d reference values, arbitrarily chosen limits were used for the proportiona l duration of some physical load factors. Studies should be carried out to assess the limits that best differentiate between safe and hazardous jobs.