Relative mechanical load on shoulder and elbow muscles in standing position when handling materials manually. A study of packing work.

When a patient with a musculoskeletal disorder returns to work after rehabilitation, the work-station should be designed so that the impaired muscle groups are less exposed to load. The work posture desirable for a particular muscle group might impose higher load on another muscle group. Since the shoulder muscles usually are stronger than the elbow muscles, a direct comparison of the loads is difficult. To make comparisons possible, the load moment about the investigated joints were divided by the counteracting maximum muscular moments, and a Muscular strength Utilization Ratio (MUR) was obtained. Using this principle, the muscular load on the shoulder and elbow was investigated in 72 different packing work postures. Different combinations of box size, box angle, edge height and weight of object handled were studied. There was a higher relative load on the shoulder than on the elbow. The concept of relating joint load to strength may serve as a guideline for how high a patient's strength should be before returning to work to avoid further injuries.