DO LIFTING BELTS PROTECT THE BACK DURING SUDDEN LOADING

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The biomechanical role lifting belts play in the prevention of low-back injury has been the subject of considerable debate. However, recent studies have shown that lifting belts do restrict the trunk motion in the frontal and transverse planes during passive motion tests and in lifting protocols. It is this through this restriction of trunk motion, or in other words the stiffening of the torso, that lifting belts may provide the greatest benefit. Epidemiological studies have indicated that sudden unexpected loading is frequently related to the onset of low-back disorder (LBD's). These events, whether they consist of a sudden load imposed upon the body, or a rapid trunk motion during a slip, create large internal loadings on the spine and it's supporting structures as the muscles attempt to null the perturbation previous research has shown that when these events can be anticipated the trunk is prepared, primarily through muscular cocontraction, such that the postural disturbance and the muscle forces loading the spine are significantly reduced. More often, however, these perturbations are unanticipated leaving little opportunity for the torso to be prepared. It is hypothesized that the stiffening effects of the lifting belt may protect workers from the extreme loads encountered during unanticipated loading events. Thus, the objective of the two proposed studies is to determine whether lifting belts protect individuals exposed to sudden loading of the torso. Twenty subjects will be recruited to serve in each of the proposed experiments. Both studies will investigate the effect of the lifting belt combined with the expectancy of loading (whether or not the subject is blindfolded), and whether the load is asymmetric with regard to the body's mid-sagittal plane. Ten trunk muscles will be sampled with surface electromyography during perturbations in which a weight, of a magnitude equivalent to 10 percent of a subject's trunk extension strength, is allowed to fall one meter prior to loading the torso. In the first study the torso will be loaded directly in that the falling weight will be attached via cables and pulleys to a chest harness worn by the subject. In this study the subjects will also be strapped into a pelvic restraint system, thereby, removing the variation due to the response of the extremities and allowing a direct evaluation belt's effect on the trunk musculature. Trunk motions will be measured by an electro-goniometer. In the second study free-standing subjects will be loaded by holding a container into which a weight is dropped. This experiment will allow an evaluation of the interplay between the trunk and the lower extremities during sudden loading and it's sensitivity to the lifting belt. Kinetic and kinematic data will be obtained using a two forceplate four camera opto-electronic motion analysis system. These data will be used in an inverse dynamic biomechanical model to determine the change in the net moments at the ankle, knee, hip, and L5/S1 level due to the lifting belt.