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Motor variability in repetitive occupational work: determinants and physiological effects


More ‘variation' is frequently suggested as an effective intervention against musculoskeletal disorders in the neck, shoulder and arm regions caused by repetitive work. Variation can be achieved by job rotation, and/or by breaking up work by periods of rest. However, these methods for increasing variation may not always be effective, and in several occupational settings, such as in standardized short-cycle industrial work, they may not even be feasible to the extent needed.

In a review article in Clinical Biomechanics, the principal researchers involved in this collaboration, Dr. Divya Srinivasan and Professor Svend Erik Mathiassen, concluded that an emerging idea to increase variation under such constraints focuses on ‘motor variability’ (MV), i.e. the intrinsic variability present in all actions controlled by the sensorimotor system, including repetitive occupational work. Although MV has been an issue for decades in motor control research, possible applications of theories and findings in an occupational context have remained largely unattended to, let alone the issue of whether this intrinsic variability can be exploited as a source of biomechanical variation without compromising work performance.


The purpose of this project is to investigate the size and consistency of MV within and between subjects, whether MV can be manipulated in occupational settings by varying different work factors. Our joint research in this area has so-far resulted in an initial position paper on the relevance of MV to occupational research, which also identified key issues for further research. We have since then documented the size and consistency of MV within and between individuals for simple linear metrics as well as for more advanced non-linear variability metrics; and investigated the influence on motor variability in a short-cycle repetitive task (pipetting) of occupationally relevant factors such as work pace, task precision and combinations of physical and cognitive loads. Preliminary investigations into the individual consistency of motor variability has also been published recently, and deeper analyses of this issue is part of the planned research for future.


The project is otherwise currently focused on understanding associations between motor variability and fatigue development using the standard pipetting work model, and has a potential to prograde into studies of whether the properties and effects of motor variability found in this controlled laboratory simulation of repetitive work are valid even in occupational work in the field, including the question of whether individual differences in variability can explain differences in susceptibility to neck-shoulder pain in repetitive work.

The questions addressed in the present project are:

  1. To which extent are effects of occupationally relevant factors such as pace generalizable across different repetitive tasks?
  2. To which extent does motor variability when performing a repetitive task influence the physiological response to that task?
  3. Do individuals have a consistent motor variability trait, that they preserve even across different tasks?