Effects of speed of lift on static and inertial moments at the joints

Abstract

Biomechanical models, often in the form of static models, are used to quantify stresses on the body. It has been shown that static models underestimate the stresses of a dynamic activity since static models fail to account for inertial effects. The primary objective of this study was to determine the effect of lifting speed on the reactive moments at the joints using several cumulative measures of whole-body stress. Five male subjects lifted a box loaded with weight based on their individual maximum acceptable weights of lift at five speeds covering the range from very slow to very fast. When averaged across the lift, the inertial component accounted for 2.5%, 5.5%, 10%, 12% and 14% of the average dynamic moment at each of the five speeds, from slowest to fastest, respectively. Relevance to industry The manual materials handling activity of lifting is a major source of work-related injury. Recommended handling strategies include slow, smooth lifting to minimize biomechanical stresses on the lifter; however, in reality handlers tend to lift at relatively fast speeds. Biomechanical studies need to account for speed of lift to accurately predict stresses to propose safer lifting strategies.