Three-Dimensional Spinal Loading during Complex Lifting Tasks

Abstract

Knowledge of the complex three-dimensional loads imposed on the spine during typical manual materials handling (MMH) tasks could provide more insights about the mechanical etiology of low back injuries in occupational settings. Comprehensive treatment of such information has been lacking. Most previous studies quantified spinal loading in terms of compressive forces alone. However, there is enough empirical and epidemiological evidence to indicate that the shear forces imposed on the spine may be more important than mere compression. Hence, the purpose of this study was to assess, in-vivo, the three-dimensional complex spinal loading associated with lifting tasks. Subjects performed simulated lifting tasks with varying workplace characteristic. An EMG-assisted model provided the continuous three-dimensional spinal loads. Asymmetric (complex) lifting tasks showed distinctive loading patterns from those observed under symmetric conditions. Simultaneous occurrences of spinal loads in all three directions (compression and shear forces) were patterns unique under the “risky” asymmetric lifting conditions. These situations could be identified and abated through proper workplace design. In conclusion, this approach allow the determination of the magnitudes and temporal occurrence(s) of complex spinal loading, and assess the sensitivity of these loading patterns to workplace characteristics.