Is there a Lateral Transfer Distance that Minimizes Twisting and Lateral Bending Motions of the Spine?

Abstract

Studies have shown that twisting and lateral bending postures and motions increase the risk of low back disorders in manual handling tasks (Marras et al., 1993; Punnet et al., 1991). These motions are often associated with asymmetric lifting. Thus, it has been hypothesized that one means for controlling these motions is through carefully designing the layout of the workplace. We hypothesized that spatially separating a lift's origin and destination to encourage stepping/turning of the body during a manual transfer task would reduce these motions. At the same time, however, the added distance may increase the tendency to reach, therein increasing the amount of forward bending, increases handling time, and may increase the physiologic cost. Thus, the objective of the current study was to determine if there is a separation distance between a lift's origin and destination during the lateral transfer of boxes that minimizes the lateral bending and twisting motions on the spine while not increasing the amount of forward bending due to reaching. The study was performed by having 29 male volunteers transfer boxes between two conveyors spaced .50, .75, 1.0, 1.25, 1.50, and 1.75 meters apart. Transfers were performed using loads of 9.5 and 16.5 kg. Spine kinematic data were collected with a magnetic motion capture system. The data from the box pick up and the box placement were analyzed separately. The twisting motions associated with the box placement were significantly affected by the transport distance (p=.007). However, the twisting motion when pick up the box, while showing a trend toward less motion with a 1 meter transport distance was not significantly different across the transport distances (p=.15). The lateral bending motions, both during the box pick up and the box placement were significantly affected by the transfer distance (p<.05). Overall our findings suggest twisting and lateral motions would both be minimized when the transfer distances were between 1 and 1.25 meters.