A biomechanical modelling of body weight effects on a manual lifting task

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Abstract
This research utilized a biomechanical approach for the investigation of body weight effects in a manual-lifting activity. Following a 3-day training session, 10 male subjects performed 6 tasks in 12 trials. For each trial, the subject was directed to use a free style posture to lift a weighted box from the floor to a 0.762m high shelf. In order to evaluate the forces and torques generated by the external load and the body weight acting on the articulations and vertebra during the lifting task, the experimenter used a high-speed camera to record the lifting activity, a GP-8 Sonic Digitizer to translate the motion into coordinates, and a biomechanical program to calculate the forces acting on the L5/S1 disc, the maximum abdominal force,and the torque acting on the abdomen. After the statistical analysis, two regression models were developed, which provide a convenient and useful means to quantify the maximum compressive and shear forces acting on the low back area during a sagittal plane-lifting activity. The model for the maximum compressive force acting on the L5/S1 disc in kilograms accounted for 95% of the variability in observed data (R2 = 0.9506); the model for the maximum shear force acting on the same disc in kilograms accounted for 93% of the variability in observed data (R2 = 0.9269).