Abstract
The substantial kinematic degrees-of-freedom available in human movement lead to inherent variations in a repetitive movement, or motor variability (MV). Growing evidence suggests that characterizing MV permits a better understanding of potential injury mechanisms. Several diverse methods, though, have been used to quantify MV, but limited evidence exists regarding the merits of these methods in the occupational context. In this work, we explored different classes of methods for characterizing MV during symmetric and asymmetric box lifting tasks. Kinematic MV of both the whole-body center-of-mass (COM) and the box were quantified, using metrics derived from a linear method (Standard Deviation), a non-linear method (Sample Entropy; an index of movement regularity), and a novel application of an equifinality method (Goal Equivalent Manifold; an index related to the set of effective motor solutions). Our results suggest that individuals manipulate regularity and the set of effective motor solutions to overcome unwanted motor noises related to the COM. These results, together with earlier evidence, imply that individuals may prioritize stability over variability with increasing task difficulty. Task performance also appeared to deteriorate with decreasing variability and regularity of the COM. We conclude that diverse metrics of MV may be complimentary to reveal differences in MV.
Highlights
The human body has substantial kinematic degrees-of-freedom that can be used to perform specific tasks, and a challenging question is how the central nervous system (CNS) can overcome such kinematic redundancy[1]
Given the evidence that motor variability (MV) might be associated with task performance and injury risks, we suggest that quantifying the extent of MV in the context of repetitive lifting may identify new approaches to evaluate musculoskeletal disorders (MSD) risk factors and performance related to this important occupational task
We found that individuals exhibited different strategies to control the BOX and the COM during repetitive lifting/ lower tasks
Summary
The human body has substantial kinematic degrees-of-freedom that can be used to perform specific tasks, and a challenging question is how the central nervous system (CNS) can overcome such kinematic redundancy[1]. Some biomechanists have hypothesized that increased MV may be beneficial, in terms of preventing injury and pain, suggesting that more variations in a repetitive task decrease mechanical loads on specific soft tissues, and that this mechanism may prevent the development of pain[9,17]. In support of this hypothesis, individuals who developed pain had a lower www.nature.com/scientificreports/. Given the evidence that MV might be associated with task performance and injury risks, we suggest that quantifying the extent of MV in the context of repetitive lifting may identify new approaches to evaluate MSD risk factors (e.g., task symmetric) and performance related to this important occupational task
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