Kinetic And Kinematic Adaptations To Use Of A Personal Lift Assist Device

Abstract

The purpose of this work was to quantify the effect of the personal lift assist device (PLAD) on kinetic and kinematic variables commonly indentified as risk factors for low back pain (LBP). As such, three investigations were undertaken to document adaptations that occur as a consequence of wearing the PLAD. The first study involved an investigation of the effects of the PLAD on intervertebral compression and shear, using an EMG-assisted biomechanical model across a range of trunk flexion. Muscle activation (EMG), trunk posture, and PLAD support data were input into a biomechanical model that estimated L4/L5 joint loads. Use of the PLAD significantly reduced joint compression across the range of trunk flexion. Significant changes in shear were also found, although this was varied across conditions. The second study was conducted to quantify differences in lifting posture, lifting kinematics, and co-ordination attributable to use of the PLAD. Over two testing sessions, subjects completed a repetitive lifting task with and without use of the PLAD. Kinematic data describing lumbar spine, hip and knee motion were used to quantify lifting posture, lifting velocities, and co-ordination. The results of the study suggest that the PLAD causes users to lift with significantly less lumbar flexion and greater hip flexion. Significant changes in co-ordination were also observed, reflective of motor adaptation to the assistance provided by the PLAD. The final study was conducted to investigate the effect of the PLAD on active trunk stiffness. Subjects were required to assume a series of static, symmetrical flexed postures. Muscle activation (EMG), trunk posture, and PLAD stiffness data were input into a stability model that estimated active trunk stiffness. Up to 15 degrees of flexion, the PLAD increased the overall stiffness of the trunk. However, use of the PLAD significantly reduced the active stiffness of the trunk as flexion increased. This effect was consistent across PLAD conditions. Further research is needed to confirm these findings and evaluate a potential redesign. In general, the results of these studies illustrate the potential for the PLAD to be used as an ergonomic intervention for industrial tasks requiring lifting and/or flexed static postures.