Design and instrumentation of a mechanical personal lift augmentation device (PLAD) for manual lifting tasks

The purpose of this study was to investigate the effectiveness of a personal lift augmentation device (PLAD) at reducing the spinal loading at the L4/L5 joint during lifting tasks. The PLAD is an on-body ergonomic aid that has elastic elements that lie external to the erector spinae muscles where these elastic elements are stretched during the down phase and return their elastic energy to the lifter during the up phase of the lift.;Results confirmed that the PLAD reduced the L4/L5 compression and shear forces by 43 Nm to 53 Nm which represented a 20% to 30% reduction based on a mathematical solution alone. 3D estimation of the dynamic moments about L4/L5 joint was used to evaluate the efficacy of the PLAD. Three-way ANOVAs were used to assess the PLAD/No PLAD conditions, three symmetric lifting styles (stoop, squat, freestyle) and three different loads (5 kg, 15 kg, 25 kg). The PLAD caused a 14% to 20% reduction in L4/L5 integrated moment magnitudes. The lumbar iEMG was reduced by 14% and the thoracic iEMG was reduced to 27% when wearing the PLAD.;Another study was done in parallel to develop and validate a biomechanical model that will be used for simulations using two approaches: the Hof link segment model and custom-made 3D Visual Nastran 4D (VN4D) virtual model. The VN4D model was highly correlated (r=0.99) to the Hof model.;Nine Fastrak(TM) 3D sensors were attached to specific body segments in order to examine a number of kinematic variables and calculate the L4/L5 moments by means of a link segment model and a custom designed Visual Nastran 4D (VN4D) model. The myoelectric signals recorded from four bilateral muscle groups of the trunk (lumbar erector spinae, thoracic erector spinae, rectus abdominus and external obliques) were used to determine the total amount of integrated electromyographic (iEMG) during the lifting tasks. Six strain gauges in series with the PLAD elastic elements provided an assessment of the PLAD's contribution to each lift and a switch was used to synchronize the data and indicate the start of the up phase of the lift. To collect comparative data between the PLAD and no-PLAD conditions, nine male subjects were asked to lift 5 kg, 15 kg and 25 kg loads in a box with handles using stooped, squat and freestyle lifting techniques in both symmetric and asymmetric postures. The asymmetric lifting trials were only used for a validation of the VN4D model.