Task rotation effects on upper extremity and back muscle activity.

Job rotation is an intuitive approach to distributing work to minimize muscular fatigue. The purpose of the current study was to evaluate rotation between lifting and gripping on muscle activity and effort. Ten male participants performed all 4 combinations of two 15 min tasks in 30 min trials split between separate days to prevent fatigue. The tasks of lifting a 12 kg box and gripping at 20% of maximum were performed 6 times per minute (5 s work: 5 s rest). Muscle activity (percentiles, gaps) and perceived effort were significantly affected by the task combinations. The forearm and upper erector spinae muscles did not benefit as greatly from rotating between lifting and gripping tasks as the lower erector spinae, deltoid or trapezius. In addition to gross task differences, overlaps in muscle activity between "low back" and "upper extremity" tasks must be considered when creating effective job rotation schemes.