Maximum forces and joint stability implications during in-line arm pushes

Abstract

Current ergonomic software packages have no way of determining manual arm strength limits when the force vector passes directly through the elbow and shoulder, such that the moment demands on those joints are very low. The first step in overcoming this dilemma is to understand what the arm force limitations are when there is no moment to balance. Sixteen participants generated isometric in-line arm forces at varying intensities. Surface electromyography was used to monitor individual muscle activity, which was used in combination with moment arm estimates, to make inference about elbow stability. There was a significant difference in the average maximum forces produced by males compared to females, such that the 25th percentile maximum in-line arm push force is suggested to be 636 N for males and 359 N for females. Our force limits can be easily implemented into any ergonomic assessment tool as boundaries for maximum in-line arm forces.