The influence of job rotation and task order on muscle fatigue: a deltoid example.

Despite frequent use in industry, job rotation lacks robust confirmation as an effective method to limit exposure. This study investigated two tasks that involved the deltoid muscle. We examined two major factors in the context of muscle fatigue: the presence of rotation between tasks, and the order of task rotation if rotation was present. Participants performed four task combinations (coded AA, AB, BA, BB) of two tasks that were intended to produce fatigue (A: repetitive shoulder flexion; B: repetitive shoulder abduction). All tested conditions resulted in lower maximum force production capability (mean range of 78-88% of original strength), in this order of decreasing magnitude: BB --> AB --> BA --> AA, though differences between successive levels were not always significant. Specific muscle results supported this progression of strength decreases. For tasks with different muscular demands (AB and BA), it was less fatiguing to rotate between them than to only perform the more demanding task (BB). The order of rotation between tasks (AB vs. BA) did not influence muscle fatigue indicators. These findings help to assess the effectiveness of rotating between different tasks in reducing muscular fatigue or exposure. They also indicated a low apparent influence of task order on terminal fatigue characteristics for the task combinations evaluated.