Effects of Rotation Frequency and Starting Task on Localized Muscle Fatigue and Performance During Simulated Assembly Work

OCCUPATIONAL APPLICATIONS This study simulated rotating between assembly tasks at two different intensity levels performed for a total duration of 1 hour, during which rotation occurred every 15 minutes, every 30 minutes, or not at all. Under the scenario studied here, rotation reduced shoulder muscle fatigue compared to only performing a higher intensity task and increased fatigue compared to only performing a lower intensity task. Neither rotation frequency nor starting task significantly affected fatigue or performance. Based on the results, rotation frequency and starting task may not need substantial consideration when designing rotation schedules or plans. Generalizing the current results to actual occupational tasks, however, may be limited due to the inclusion of only two tasks, the constrained nature of the task, and the small sample size. TECHNICAL ABSTRACT Background: Rotating between tasks is widely used and considered to reduce the risk of work-related musculoskeletal disorders, though there is limited evidence that it is effective in doing so. Purpose: This study assessed the effects of rotation during assembly work involving the upper extremity, specifically focusing on rotation frequency and starting task, on shoulder muscle fatigue and task performance when included tasks loaded the same muscle group. Methods: Twelve participants completed six experimental sessions during which a simulated repetitive assembly task was performed for 1 hour either with or without rotation. When rotation occurred, it was between two intensity levels corresponding to two working heights. Results: As expected, rotating between the tasks reduced shoulder muscle fatigue compared to only performing the higher intensity task and increased fatigue compared to only performing the lower intensity task. Neither rotation frequency nor starting task had significant or consistent effects on fatigue or task performance. Conclusions: While varying the intensity level of tasks included in rotation schedules reduced muscle fatigue, this effect was not influenced substantially by either rotation frequency or starting task during the moderately demanding upper extremity assembly task examined here.