Spinal Loading During One and Two-Handed Lifting

Abstract

Background: Lifting at work remains one of the most highly studied potential risk factors for low back disorders, but most of the studies that have been conducted on this topic focus on lifting scenarios in which two hands are used to lift the weight. Few investigations have examined one-handed lifting scenarios, as might be observed when lifting objects from industrial storage bins or stocking products onto shelves. Moreover, there remains a need to re-examine one versus two-handed lifting scenarios utilizing a more advanced and accurate biomechanical model than was used previously (Ferguson et al., 2002; Kingma and van Dieen, 2004; Marras and Davis, 1998). The objective of this study was to quantify biomechanical loads imposed upon the lumbar spine during one-handed lifting versus two-handed lifting, specifically in relation to any interaction effects present between the number of hands used to perform the lift and external lifting conditions like the lift origin or object weight. Methods: Thirty subjects (15 male, 15 female) were recruited for this laboratory study. In each experimental task, subjects lifted one of three medicine balls (of the same size/shape but differing in weight) with either one or two hands from the lift origin predefined by the study design to a common lift destination directly in front of the body. All one-handed exertions were performed with the dominant hand, and asymmetric conditions were tested on the dominant side of the body. Independent variables included lift origin height (ankle, knee, waist), lift origin asymmetry (0 degrees, 45 degrees, 90 degrees), load weight (2.7 kg, 7.3 kg, 11.4 kg), horizontal distance of the lift origin from the body (40 cm, 70 cm), and the number of hands used to perform the lift (one, two). An EMG-driven biomechanical spine model was implemented to evaluate lumbar spinal loads in compression, anterior/posterior (A/P) shear, and lateral shear (Dufour et al., 2013; Hwang et al., 2016a, 2016b). Results and Discussion: One-handed lifting resulted in 6% lower spinal compression and 16% lower A/P shear loads than two-handed lifting on average, but lateral shear was increased by 23% for one-handed lifting relative to two-handed lifting (p<0.001). Consistent with Marras and Davis (1998), spinal compression increased with increased lift origin asymmetry in two-handed lifting but decreased with increased lift origin asymmetry in one-handed lifting (p<0.001). The effects of using one versus two hands to perform the lift were generally amplified at lower lift origin heights, lower weights, and for the far reach distance. Effects were likely driven by differing moment exposures on the spine attributable to the weight of the torso. Conclusion: One-handed lifting resulted in lower peak spinal compression and peak A/P shear loads on the lumbar spine, so it may be preferred to two-handed lifting if the load to be lifted falls within the strength capabilities of the worker population. However, while this study shows benefits of one-handed lifting for the low back, these results should be placed in context with future studies aimed at assessing the impacts of one-handed lifting on the upper extremity. Acknowledgement: This study was funded, in part, by the Ohio Bureau of Workers’ Compensation.