Assessment of the relationship between box weight and trunk kinematics: Does a reduction in box weight necessarily correspond to a decrease in spinalloading?

Typically, the simplest and most cost-efficient ergonomic solution to offse t the rising casts of low back injuries is to reduce the box weight that is lifted. However, there is limited research on how a worker interacts with the box. In the present study, we quantify the utility of reducing the weig ht that is lifted - specifically, how changes in the box weight affect trun k kinematics, trunk moments, and ultimately, spinal loads. In the experimen t, 15 participants lifted a variety of box weights (from 9.1 to 41.7 kg) fr om knee height, carried it a distance of 5 feet (1.5 m), and placed it on a shelf at elbow height. For the lower weights, small increases in box weigh t (3-9 kg) were offset by the trunk dynamics (sagittal velocity), resulting in no difference in spinal loads. At the same time, spinal loads were foun d to be significantly higher for weights above 25 kg. Thus, when making erg onomic changes (reduction of box weight), it is important to consider how w orkers will interact with the box. These results indicate that purely weigh t-based ergonomic controls might not sufficiently reduce the risk of low ba ck disorders. Furthermore, this study provides additional evidence of the u tility of using more complex spinal load models (dynamic, multiple muscle m odels) when evaluating highly dynamic and complex tasks.