Impact of Order and Load Knowledge on Trunk Kinematics During Repeated Lifting Tasks

Objective: To determine if lifting random unknown weights is more detrimental than lifting sequences of unknown weights and to investigate whether load knowledge impacts the effect of lifting random box weights. Background: Much research has investigated lifting under known load conditions, but few studies have investigated unknown loads, especially when presented in random order. There has been some documentation of alteration in trunk mechanics when there is an overestimation of the unknown load. Method: Ten men and 10 women performed three lifting tasks: random unknown, random known, and same weight. A lumbar motion monitor was used to collect kinematic data, and Borg's Rating of Perceived Exertion (RPE) and a task risk rating were also assessed. Results: Both presentation order and load knowledge impacted trunk kinematics during repeated lifting tasks. However, these differences were relatively low in magnitude. Furthermore, kinematic response and perceived risk and exertion for these conditions varied between genders. Conclusion: Lifting random unknown loads appears to alter kinematic responses, particularly for men. Women attempt to modify the effect of random unknown loads by changing the lifting style through alterations in upper limb motions (e.g., drag box toward them prior to lifting). However, a need remains for a more comprehensive biomechanical investigation (e.g., spine loading) into the effects of random unknown loads because many of the effect sizes were small. Application: Small kinematic adaptations resulting from tasks involving unknown and random loads may be mediated by the use of visual cues, order of presentation, or a change in lifting style.