The effect of complex dynamic lifting and lowering characteristics on trunk muscles recruitment

A better understanding of how the neuromuscular spinal system behaves during lifting and lowering could provide more insight about potential causes of occupational low back disorders (LBDs), and could help in the prevention and rehabilitation process of these disorders. The purpose of this study was to quantify trunk muscle activities under various whole-body free-dynamic symmetric and asymmetric complex lifting and lowering tasks. Eleven male subjects with no prior history of LBDs participated in the study. Electromyographic activities of ten trunk muscles were monitored while subjects either symmetrically or asymmetrically lifted and lowered a box under three different speeds and three weights. The results showed that all ten muscles were responsive to various experimental conditions with the erector spinae and internal oblique muscles showing the greatest response. Substantial electromyographic activities were observed in muscles that were on the contralateral side of the load. Lowering conditions yielded consistently lower muscular activities than their corresponding lifting conditions. These results show that it is essential to consider multiple trunk muscles in modeling efforts of quantifying spinal loading, as well as for back rehabilitation research purposes.