An electromyographic study of strength and upper extremity muscle activity in simulated meat cutting tasks.

Meat cutting has long been associated with a high incidence rate of upper extremity musculoskeletal disorders. This study examined upper extremity muscle activities and force exertion capabilities to identify postures which have potential for causing overexertion injuries. Fifteen subjects exerted force against a handle in postures similar to those observed in the meatpacking industry. Exertion level, direction of exertion, handle height, reach distance and grip type were varied. Activity in the posterior deltoid, biceps brachii, triceps brachii, extensor digitorum and flexor digitorum superficialis was monitored via surface electromyography (EMG). The ratio of normalized EMG activity to force produced during the exertion was computed for each muscle under each condition. The results showed that handle position had a significant effect on force exertion capability and the EMG/force ratio in all muscles. Force exertion capability was maximized, and the EMG/force ratio was generally minimized when participants pulled downward on a handle positioned at full arm's reach above the shoulder. For vertical cuts, force decreased and muscle activity generally increased as the handle height was lowered. For horizontal cuts, the full reach distance tended to allow greater force exertion with lower EMG/force ratios. The stab grip also tended to be associated with higher forces and lower EMG/force ratios than the slice grip. This study supports the premise that musculoskeletal stresses in meatpacking tasks can be altered through tool and workstation redesign. The data provided herein may be useful in selecting design modifications that reduce biomechanical stress on the upper extremities.