An assessment of complex spinal loads during dynamic lifting tasks

Study Design. An electromyogram-assisted free-dynamic lifting model was used to quantify the patterns of complex spinal loads in subjects performing various lifting tasks. Objectives. To assess in vivo the three-dimensional complex spinal loading patterns associated with high and low risk lifting conditions that matched those observed in industrial settings. Summary of Background Data. Combined loading on the spine has been implicated as a major risk factor in occupational low back disorders. However, there is a void in the literature regarding the role of these simultaneously occurring complex spinal loads during manual lifting. Methods. Eleven male subjects performed symmetric and asymmetric lifting tasks with varying speed and weight. Reactive forces and moments of L5-S1 were determined through the use of electrogoniometers and a force plate. An electromyogram-assisted model provided the continuous patterns of three-dimensional spinal loads under these complex lifting tasks. Results. The results showed that complex dynamic motions similar to those observed in risky industrial tasks generated substantial levels of combined compressive and shear loads. In addition, higher loading rates were observed under these conditions. Unlike loading magnitudes, loading rate was a better indicator of dynamic loading because it incorporated both the duration and magnitude of net muscle forces contributing to total spinal loading during the lifting conditions. Conclusions. Quantification of spinal combined motions and loading in vivo has not been undertaken. This study provided a unified assessment of the effects of combined or coupled motions and moments in the internal loading of the spine. Dynamic lifting conditions similar to those observed in risky industrial situations generated unique complex patterns of spinal loading, which have been implicated to pose a higher risk to the spinal structure. The higher predicted loading and loading rate during asymmetric lifting conditions can be avoided by appropriate ergonomic workplace modifications.