Effect of initial horizontal object position on peak L5/S1 moments in manual lifting is dependent on task type and familiarity with alternative lifting strategies.

This study investigated whether the effects of initial horizontal object position on peak L5/S1 total moment (PTM) are affected by task type or familiarity with alternative lifting strategies during manual lifting. Nine subjects lifted low-lying boxes from far and close initial horizontal positions in a typical laboratory lifting task (without any transportation of the load) and in a more realistic lifting task in which the box was transported to a location at a few metres distance. Subsequently, subjects were familiarised with alternative lifting strategies (e.g. shifting and tilting) and they then repeated the more realistic lifting task. Compared with the typical laboratory lifting task, the more realistic lifting task resulted in 6% larger PTMs for the close-positioned box. Familiarisation with alternative lifting techniques resulted in a 10% reduction in PTMs for the far-positioned box. As a result, the effect of initial horizontal box position on PTMs was smaller for the more realistic lifting task than for the typical laboratory lifting task and vanished after familiarisation with alternative lifting strategies. STATEMENT OF RELEVANCE: This study showed that the effect of horizontal box position on peak L5/S1 moments is dependent on the type of lifting task (comparing a typical laboratory simulated lifting task with a more realistic task involving carrying the load for a short distance) and familiarity with alternative lifting strategies. Therefore, it is recommended that back loading should be evaluated in a realistic simulation of the work situation or at the workplace itself.