The combined influence of task accuracy and pace on motor variability in a standardised repetitive precision task

Abstract

Thirty-five healthy women, experienced in pipetting, each performed four pipetting sessions at different pace and accuracy levels relevant to occupational tasks. The size and structure of motor variability of shoulder and elbow joint angles were quantified using cycle-to-cycle standard deviations of several kinematics properties, and indices based on sample entropy and recurrence quantification analysis. Decreasing accuracy demands increased both the size and structure of motor variability. However, when simultaneously lowering the accuracy demand and increasing pace, motor variability decreased to values comparable to those found when pace alone was increased without changing accuracy. Thus, motor variability showed some speed-accuracy trade-off, but the pace effect dominated the accuracy effect. Hence, this trade-off was different from that described for end-point performance by Fitts' law. The combined effect of accuracy and pace and the resultant decrease in motor variability are important to consider when designing sustainable work systems comprising repetitive precision tasks.

Abstract

Practitioner summary: Variability in movements and/or muscle activities between repeats of the same repetitive task is associated with important occupational outcomes, including fatigue, discomfort and pain. This study showed that simultaneously decreasing accuracy and increasing pace in short-cycle repetitive work led to decreased motor variability in arm movements, indicating less favourable ergonomics conditions.

Keywords::

• cyclic movements
• Fitts' law
• kinematics
• linear and nonlinear variability
• motor control
• speed-accuracy trade-off

Acknowledgements

We would like to acknowledge the contributions of Nisse Larsson and Majken Rahm for their assistance in the collection of data.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by grants from the Swedish Research Council for Health, Working Life and Welfare (Forte Dnr. 2009-1761 and 2011-0075). The sponsors did not influence the collection, analysis and interpretation of data, writing of the manuscript or the decision to submit the manuscript for publication.