Biomechanical Analysis of Asymmetric and Dynamic Lifting Task

BIOMECHANICAL ANALYSIS OF ASYMMETRIC AND DYNAMIC LIFTING TASK by Xiaopeng Jiang Lifting tasks is one of the leading causes of occupational lower back disorders (LBD). Aimed at deriving internal forces of human musculoskeletal system during lifting, biomechanical models are utilized to address this problem. This thesis provides an indepth literature review of such modeling, and the results of experiments used to address LBD issues. An isometric pulling experiment was conducted to study the correlation between electromyography (EMG) and muscle forces predicted by AnyBody Modeling SystemTM with increasing hand loads, and infinite order polynomial (min/max) optimization criterion predicted percentage of maximum muscle forces 98% correlated with normalized EMG. In a separate study, motion data during lifting of 13.6kg (30lb) weight at 0°, 30° and 60° asymmetry was collected by the OptiTrackTM six-camera motion capture system to drive the AnyBodyTM model dynamically. Erector spinae was the most activated muscle during lifting. When the lifting origin became more asymmetric toward right, the right external oblique was more activated, and complementarily the right Internal oblique was less activated. Because oblique muscles with larger moment arms can support an external moment more efficiently, and the subject squatted more as the lifting origin became more asymmetric, L5/S1 joint forces decreased. This study contributes to the design and evaluation of lifting tasks to minimize the cost of LBD. BIOMECHANICAL ANALYSIS OF ASYMMETRIC AND DYNAMIC LIFTING TASK