TRUNK MUSCLE USE DURING PULLING TASKS - EFFECTS OF A LIFTING BELT ANDFOOTING CONDITIONS

Pulling tasks require the torso to act as a rigid link in order to fac ilitate the force transmission between the ground and the hands. In th is study, we tested the hypothesis that a lifting belt increases the r igidity of the torso, thereby increasing pulling strength or reducing trunk muscle forces, or both, as pulling tasks are performed. Twelve v olunteers performed maximal and submaximal isometric pulling exertions ; the latter were performed on nonslippery and slippery surfaces. Elec tromyographic data from 8 trunk muscles, trunk kinematic data, and gro und reaction forces were sampled during each exertion. Results indicat ed that the lifting belt had no effect during maximal exertions on the maximal pull forces generated or the muscle recruitment levels, irres pective of the pulling posture. The lifting belt did not affect the EM G data obtained during the submaximal (40% of maximum) exertions, even when participants pulled on a slippery surface. However, the slippery surface increased the coactivation within the trunk musculature, perh aps stiffening the torso in the event of a slip. The absence of a stat istical interaction effect between the lifting belt and the footing co ndition (slipperiness) indicates that the belt did not alter the coact ivation pattern and hence was not relied upon by the participants as a protective mechanism. The data presented here will assist those who m ust make decisions regarding lifting-belt use and those who train indi viduals in manual materials handling techniques.