Rotation During Lifting Tasks: Effects of Rotation Frequency and Task Order on Localized Muscle Fatigue and Performance

Abstract

Though widely considered to reduce the risk of work-related musculoskeletal disorders, there is limited evidence suggesting that rotating between tasks is effective in doing so. The purpose of the current study was to quantify the effects of rotation and parameters of rotation (frequency and task order) on muscle fatigue and performance. This was done using a simulated lifting task, with rotation between two levels of loading of the same muscle groups. Twelve participants completed six experimental sessions during which repetitive box lifting was performed for one hour either with or without rotation. When rotation was present, it occurred every 15 minutes or every 30 minutes and was between two load levels (box weights). Rotation reduced fatigue and cardiovascular demand compared to the heavier load without rotation, with a mean reduction of ∼33% in perceived discomfort and a ∼17% reduction in percentage of heart rate reserve. Further, rotation increased fatigue and cardiovascular demand compared to the lighter load without rotation, with a mean increase of ∼34% perceived discomfort and a ∼19% increase in percentage of heart rate reserve. Neither rotation frequency nor task order had definitive effects, though maximum discomfort ratings were nearly 20% higher when starting with the lighter load task. These parameters of rotation should be further evaluated under more realistic task conditions.

Is rotating between static and dynamic work beneficial for our fatigue state?

“…3). Previous studies investigating the effect of rotation frequency between lifting of 10% and 20% body weight (Horton et al, 2015), shoulder flexion and abduction (Raina and Dickerson, 2009), and static shoulder exertions at 15% and 30% MVC (Horton et al, 2012) on manifestations of muscle fatigue and perceived fatigue are in line with our findings. Because we clearly saw more development of perceived fatigue in the low compared to the high rotation frequency protocols, the two experimental tasks may not have been different enough in terms of muscle activation patterns, or the effects of the rotation schemes may not have been present yet within 1 h. We considered the EMG variability and its spatial centre of activity parameters because they could be influenced by manifestations of muscle fatigue.…”

“…These studies rotated between tasks that differed considerably in the type of task and also the muscles activated during each task. Two studies that specifically rotated between tasks, which only differed in the load intensity during static shoulder exertions (Horton et al, 2012) and lifting (Horton et al, 2015), did not find changes in manifestations of muscle fatigue. Raina and Dickerson (2009) investigated the alternation between two fairly similar tasks, shoulder flexion and shoulder abduction, which have a different muscular demand; however, they did not find significant effects of rotation on manifestations of muscle fatigue or perceived exertion either.…”

“…Hand-arm tasks, which particularly load the shoulder-neck muscles, can either be relatively static (e.g., Raina and Dickerson, 2009) or more dynamic (e.g., Horton et al, 2015). Several studies investigated differences in physical demands between static and dynamic arm work at similar force levels.…”

Effects of Vertical Lifting Distance on Upper-Body Muscle Fatigue

“…The varying posture and contraction torque notably affect the muscle fatigability of the trapezius and multifidus during manual handling [20,21]. Otherwise, rotation of operating and resting in the process of the short-term MMH tasks, whose frequency varies corresponding to the workload, could reduce/increase muscle fatigue compared to performing a coherent heavier-load-leveled/lighter-load-leveled task without resting [22]. Moreover, during the sEMG detection, the impact of postural variation, compared to the task rotation, on the conventional manifestation of shoulder muscle fatigue is obviously easier to detect [23].…”

“…Therefore, this study has focused on the fatigue comparison between the targeted muscles, which are located on the upper-arm, shoulder, waist, respectively. All targeted muscles, including biceps brachii, upper trapezius, and multifidus, have proved to be sensitive to the fatigue-risk factors [15,21,22,26]. The fatigable muscle is capable of being discerned through comparing the myoelectric manifestation of muscle fatigue, while its capacity could be evaluated through the electromyographic mean-power-frequency fatigue threshold test (MPFFT).…”