TRUNK KINEMATICS OF ONE-HANDED LIFTING, AND THE EFFECTS OF ASYMMETRY AND LOAD WEIGHT

This study investigated trunk kinematic differences between lifts perf ormed using either one hand (unsupported) or two hands. These effects were studied while beginning the lifts from different asymmetric start ing positions and while lifting different load weights. Each subject l ifted a box from a lower to an upper platform under one- and two-hande d lifting conditions. Subjects wore a lumbar spine electrogoniometer, from which relative motion components were calculated in the trunk's t hree cardinal planes. Results of this study showed that one-handed lif ting resulted in significantly higher ranges of motion in the lateral and transverse planes and greater flexion in the sagittal plane. Back motion characteristics previously found to be associated with low back disorders were all significantly higher for one-handed lifts. The two -handed lift technique, on the other hand, produced overall faster tru nk motions in the sagittal plane and equal or larger acceleration and deceleration magnitudes in all planes of motion. Increases in load asy mmetry affected trunk kinematics, in that magnitude values for range o f motion, velocity and acceleration became much greater with increasin gly asymmetric load positions. Increasing the load weight appeared to have less of an effect on trunk kinematics, with increases in position mostly occurring during sagittal and lateral bending. These results s uggest that unsupported one-handed lifting loads the spine more than t wo-handed lifts, due to the added coupling. Applying these results to a previously developed model, one-handed lifting was also found to inc rease one's risk of suffering a low back disorder.