Postural stability and risk of slips in lifting tasks: Effects of load weight and load knowledge

Load transfer during lifting leads to increased postural perturbations that may compromise postural stability, so lifting is an occupational task associated with high fall risk. This study aimed to gain improved knowledge about fall risk in lifting tasks. The effects of both load weight and load knowledge were examined. Load weight was set at three levels according to individuals' maximum acceptable lifting capacity. Unlike previous studies, load knowledge was set by considering load material fragility. Twenty-four male participants were involved in the experimental study, in which they were instructed to perform both symmetric and asymmetric lifting tasks under conditions defined by various combinations of load weight and load knowledge. Fall risk was assessed by using measures accounting for postural stability and risk of slips. The results showed that when being defined near individuals' maximum acceptable lifting capacity, increased lifting load weight not only improved postural stability in the rising phase of lifting, but also increased the risk of slips. These findings suggest that improved postural stability due to increased load weight in the rising phase could be a compensatory postural control strategy for the increased risk of slips so as to maintain balance and avoid the occurrence of a potential fall. We also found that load knowledge of fragility and weight may not contribute to fall risk reduction during lifting. The findings obtained from the present study are useful for practitioners to design safe lifting tasks.