Effects of a lifting belt on spine moments and muscle recruitments after unexpected sudden loading

Study Design. Ten men and eight women participated in a repeated-measures e xperiment in which sudden loads were applied unexpectedly to a container he ld in the hands, Three independent variables were investigated: lifting bel t use, preload, and load symmetry. Objectives. To determine whether a lifting belt would help protect the spin e in sudden symmetric and asymmetric loading situations. Summary of Background Data. Unexpected loading events have long been associ ated with the onset of back pain. Based on work showing that lifting belts restrict motion the torso, the hypothesis was that a lifting belt would sti ffen the spine, thereby protecting its supporting tissues. Methods. A weight, equal to 7.5% of the subjects' trunk extension force, wa s allowed to fall 1 m before the bottom of a box held by blindfolded subjec ts was pulled. Kinetic and kinematic data, obtained from two force plates a nd a magnetic motion measurement system, were used in a three-dimensional, dynamic, linked-segment biomechanical model to calculate spine moments. Ele ctromyogram data were simultaneously obtained from eight trunk muscles. Results. The belt reduced the forward bending of the spine during the symme tric loadings. In the men, the belt also reduced the forward flexion moment acting on the spine. The belt restricted lateral bending in the women and men, when the box was preloaded, The peak electromyogram amplitudes from po sterior contralateral erector spinae and latissimus dorsi muscles increased during the asymmetric loadings, whereas three ipsilateral muscles were les s active. Conclusions. The conflicting moment and electromyographic results, combined with the influence of load symmetry, preload, and gender make the benefits of the lifting belt difficult to delineate. Although the data support the hypothesis that the belt stiffens the torso's response to sudden loading, t he effects are small, and considerable individual differences exist. The fi ndings show that during unexpected sudden loading, a belt may reduce the ne t external moment loading. At the same time the belt appears to alter the m uscle response strategy so that the belt's overall effect on an individual' s safety is hard to determine.