Measurement of physical work capacity during arm and shoulder lifting at various shoulder flexion and ad/abduction angles

The purpose of this study was to provide information on physical work capacity during arm and shoulder lifting at various shoulder flexion and ad/abduction angles. We measured the maximum voluntary contractions (MVCs) in 20 male participants during controlled one-arm lifting. The lifting involved upward motion of the scapula at various shoulder angles. Simultaneously, the electromyographic (EMG) activity of 3 shoulder muscles and psychophysical workload were also recorded. The various measurements were compared to provide a multidimensional assessment of the physical work capacity of the shoulder at various working angles. In particular, 90 and 120 degrees of flexion, 30 degrees of adduction, and 90 degrees of abduction were found to be the most vulnerable angles based on the measured MVCs. The average root mean square value of the EMG increased most significantly at 90 to 150 degrees of flexion and at 30 and 60 degrees of abduction. Slightly different measurements were compared to validate the results. In addition, a 3-D static biomechanical model was used to show whether the estimated shoulder workload matched the measured physical capacity of the shoulder. In conclusion, these results may help ergonomists to identify shoulder angles associated with a relatively high risk of injury, and to match the workload with the physical capacity of the shoulder. Task-specific information on shoulder work capacity is needed in the manufacturing and shipbuilding industries to protect workers from acute injuries and cumulative trauma disorders of the shoulder. Experimental results provide various data on shoulder work capacity during realistic multijoint arm and shoulder lifting, and should help lead to improvements in workplace ergonomic design. (C) 2003 Wiley Periodicals, Inc.