Changes in the amount and structure of motor variability during a deboning process are associated with work experience and neck-shoulder discomfort

In this field study, the size and structure of kinematics variability were assessed in relation to experience and discomfort during a deboning task. Eighteen workers divided in groups with low/high experience and with/without neck-shoulder discomfort participated. Standard deviation and coefficient of variation (amount of variability), as well as approximate entropy and sample entropy (complexity) and, correlation dimension (dimensionality) were computed for head-shoulder, shoulder-hip and elbow-hip displacement in the vertical direction. A longer work experience was associated with shorter work cycle duration and decreased amount of variability while complexity increased for the head-shoulder displacement, P<0.05. Shorter work cycle, lower amount of variability and, lower dimensionality for the head-shoulder displacement were found in relation to discomfort, P < 0.05. While the amount of variability, complexity and dimensionality increased for the elbow-hip displacement, P<0.05. These findings Suggest a functional role of experience via learning effects and discomfort through compensatory mechanisms on the size and structure of motor variability. (C) 2009 Elsevier Ltd. All rights reserved.