The effect of fatigue on trunk muscle activation patterns and spine postures during simulated firefighting tasks

Abstract

The purpose of this study was to determine the effect of a fatiguing task (3 min intense stair climbing) on the adopted spinal postures and trunk muscular activation patterns during three highly physically demanding simulated firefighting tasks. Following the fatigue protocol, it was observed that individuals adopted significantly greater spinal flexion (16.3° maximum prior to fatigue as compared to 20.1° post fatigue) and displayed reduced abdominal muscle activation as compared to before the fatigue protocol (mean ranging from 16.6% maximum voluntary contraction (MVC) to 30.6% MVC prior to fatigue as compared to ranging from 14.6% MVC to 25.2% MVC post fatigue). The reduced abdominal activation may be due to a reduction in co-contraction during these tasks, which may compromise spinal stability. Reduced co-contraction combined with the increased spinal flexion may increase the risk of sustaining an injury to the low back.

Keywords:

• ergonomics
• firefighting
• fatigue
• EMG
• spine posture
• injury

Acknowledgements

The authors wish to acknowledge UW Fitness at the Lyle Hallman Institute for Health Promotion, University of Waterloo, for the use of their firefighting testing facilities. Dr Jack Callaghan is supported by a Canada Research Chair in Spine Biomechanics and Injury Prevention.