Experimental analysis of whole-body coordination changes associated with repetitive upper limb motion: what, when, why?

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Repetitive motions are often accomplished during daily life. In the workplace, upper limb repetitive tasks have been linked with musculoskeletal disorders (MSD), of which working posture and fatigue account for some of the most important risk factors. An important aspect of repetitive movement is the potential consequence of fatigue. The short-term effects of fatigue on individual muscle characteristics are well known. However, few studies have investigated the effects of fatigue across the body. Also, it is well known that the prevalence of upper limb MSD is higher in women, although the reasons for this are unclear. The general objective of this research program is to gain a better understanding of the biomechanics and control aspects of upper limb repetitive movements, in relation to the posture adopted during these movements, in healthy humans. In project 1, we will measure changes occurring in within the fatigued muscle as well as between muscles across the body to construct a time sequence of changes occurring throughout the body as fatigue develops. In project 2, subjects will perform various tasks (effort sense, movement sense, position sense) to assess the effects of fatigue on their proprioception. In project 3, the trunk will be blocked during the repetitive task, while time to fatigue and changes in whole-body characteristics are recorded. In all projects, we will also assess potential differences in the fatigue response patterns between men and women. The novelty of this research program can be attributed to the proposed multi-level experimental approaches combining both spatial and temporal analyses of integrated posture and movement characteristics, the tools used to study changes in muscle patterns and posture-movement strategies and the attempt to determine if men and women use similar strategies to adapt to fatigue. As a whole, this program has the potential to contribute to fundamental knowledge of biomechanics and motor control related to the understanding of complex motor behavior. This knowledge may in turn serve as a basis to adapt the workplace to the gender-specific characteristics of repetitive work and to prescribe work training regimens to prevent the development of MSD.