The effect of bracing availability on one-hand isometric force exertion capability

Abstract

Environmental obstructions that workers encounter can kinematically limit the postures that they can achieve. However, such obstructions can also provide an opportunity for additional support by bracing with the hand, thigh or other body part. The reaction forces on bracing surfaces, which are in addition to those acting at the feet and task hand, are hypothesised to improve force exertion capability, and become required inputs to biomechanical analysis of tasks with bracing. The effects of kinematic constraints and associated bracing opportunities on isometric hand force were quantified in a laboratory study of 22 men and women. Analyses of one-hand maximal push, pull and lift tasks demonstrated that bracing surfaces available at the thighs and non-task hand enabled participants to exert an average of 43% more force at the task hand. Task hand force direction deviated significantly from the nominal direction for exertions performed with bracing at both medium and low task hand locations.

Practitioner summary: This study quantifies the effect of bracing on kinematically constrained force exertions. Knowledge that appropriate bracing surfaces can substantially increase hand force is critical to the evaluation of task-oriented strength capability. Force estimates may also involve large off-axis components, which have clear implications for ergonomic analyses of manual tasks.

Keywords:

• bracing
• constrained working postures
• force exertion capability
• hand force
• push/pull

Acknowledgements

The partners of the Human Motion Simulation (HUMOSIM) programme at the University of Michigan sponsored the research described in this paper. HUMOSIM partners include Ford Motor Company, General Motors, Toyota Motor Corporation and the US Army Research and Development Command (RDECOM).