Handgrip and Box Tilting Strategies in Handling: Effect on Stability and Trunk and Knee Efforts

The purpose of this study was to evaluate the effect of four handgrip-box tilting strategies (right, left, backward, and no tilt of the box) on trunk and knee efforts, body posture, and the stability of 14 participants with limited experience in handling. The tasks consisted of transferring a low-lying box placed in front of the participant to a shelf of the same height at the participant's left. It was hypothesized that tilting the box could reduce trunk and knee efforts as well as body asymmetry, and improve stability. A tridimensional dynamic rigid body model was used to estimate the triaxial net muscular moment magnitudes at the trunk (L5/Sl) and at the knees. An approach to quantify the participants' dynamic stability was also included. Finally, 5 angles were computed to characterize body asymmetries. The results showed that tilting the box affected specific trunk efforts, but did not succeed in reducing trunk asymmetric efforts. However, the tilts were executed in a single direction, and it may be possible that combined tilts of the box could help reduce trunk asymmetric efforts. Tilting the box had little effect on knee loadings, and the left tilt strategy reduced participants' stability. This study showed the importance of considering the position of the box when assessing the risks encountered in asymmetrical handling.