Trunk Force Development during Static and Dynamic Lifts

Abstract

Most lifting analyses have used static models to evaluate the loading of the trunk during the performance of work. Recent research has reported many differences in trunk muscle force capability when a wide range of trunk velocities are observed. This study focused upon these differences during slow trunk velocities, which would be expected during a lift. Forty-five subjects were tested for their ability to exert torque about their low back under static and dynamic sagittally symmetric lifting conditions. Trunk muscle electromyography was used as a measure of trunk loading. The results reveal that significantly greater loading occurs under slow dynamic conditions, as compared with static conditions. Hence, static models, which assume quasistatic motion, are not good indicators of dynamic trunk load. A regression model was developed that described trunk loading as a function of trunk angle and velocity. The correlation between torque and muscle electromyography in the erector spinae muscles was also found to increase significantly as trunk velocity increased. The implication of these findings upon lifting is discussed.

Activity of deep abdominal muscles increases during submaximal flexion and extension efforts but antagonist co-contraction remains unchanged

“…When a perturbation is applied to the trunk by unexpectedly adding a load there is increased cocontraction prior to the time of loading in order to optimise the control of the impending event (Andersen et al, 2004;Chiang and Potvin, 2001;Granata and Orishimo, 2001;Krajcarski et al, 1999;Lavender and Marras, 1995;Lavender et al, 1989). Increased co-contraction stiffens the spine and reduces the displacement induced by the perturbation (Janevic et al, 1991;Lavender et al, 1989;Marras et al, 1987). Furthermore, the amplitude of any additional muscle activity in response to the perturbation is decreased (Vera-Garcia et al, 2006).…”

Comparisons of Trunk Motions and Low Back Injury Risk between Alternative Hotel Room Cleaning Methods

“…As with posture, speed of work has long been associated with spinal loading and back injuries. Marras et al [ 36 ] found spinal loads (assessed using muscle electromyography) to be significantly higher when trunk motions were dynamic compared to those measured when the trunk was static. Further, in a study by Bigos et al [ 37 ], awkward working postures and the speed with which jobs were performed together accounted for 29% of high-cost back injury claims.…”