Spine loading during asymmetric lifting using one versus two hands W ILLIAM S. M ARRAS* and K ERMIT G. D AVIS Biodynamics Laboratory, The Ohio State University, 1971 Neil Avenue, 210 Baker Systems, Columbus OH 43210, USA Keywords: Spinal loading; Asymmetry; One-hand lifting; Manual materials handling. This study documented three-dimensional spinal loading associated with asymmetric lifting while using either one or two hands to perform the task. Lift asymmetry was de®ned as a function of the load origin relative to the sagittal plane of the body. Lifts occurred at 0, 30, or 60 8 oŒ the sagittal plane on both sides of the body (lifting from the right and from the left relative to the sagittal plane). Ten subjects lifted a 13.7 kg box from one of these origins to a sagittally symmetric destination. Spinal loads were estimated through the use of a validated EMG-assisted model. Spine compression and lateral shear forces increased as the lift origin became more asymmetric. However, spinal compression and lateral shear increased by about twice the rate when lifting from origins to the left of the sagittal plane compared to lifting from origins to the right of the sagittal plane. Anterior-posterior spinal shear decreased as asymmetry increased with larger decreases occurring when lift origins occurred to the right of the sagittal plane. One-hand lifting changed the compression and shear pro®les signi®cantly. One- hand lifts using the hand on the same side of the body as the load resulted in compression forces that were approximately equal to those observed when lifting with two hands in a sagittally symmetric position. Anterior-posterior shear decreased and lateral shear increased under these conditions. These results re¯ect the trade-oŒs that must be considered among spinal forces during asymmetric lifting while using one or two hands. These ®ndings have signi®cant implications for task assessment interpretation and workplace design. 1. Introduction It has been estimated that up to 85% of the workforce will suŒer from a low-back disorder (LBD) sometime during their working lives (Spengler et al . 1986). Manual materials handling (MMH) tasks have been associated with the majority of these work-related LBDs (Snook et al . 1978, Bigos et al . 1986). MMH tasks can require the worker to lift, bend forward, bend laterally, twist, maintain static postures, carry heavy loads, or perform combinations of these activities (Snook et al . 1978, Andersson 1981, Kelsey et al . 1984, Bigos et al . 1986, Marras et al . 1993, 1995). A commonly observed work condition in industry is that of lifting from asymmetric positions (Marras et al . 1993, 1995). Lift asymmetry has been associated with decreased trunk strength (Garg and Badger 1986, Marras and Mirka 1989, Ferguson et al . 1992), a reduction in the maximum acceptable weight of lift (Garg and Badger 1986, Mital and Fard 1986, Mital et al . 1989), and more complex trunk motions (Ferguson and Marras 1992, Ferguson et al . 1992, Allread et al . 1996). *Author for correspondence. ERGONOMICS, 1998, VOL. 41, NO. 6, 817 ± 834 0014±0139/ 98 $12.00 Ó 1998 Taylor & Francis Ltd