Kinematics and Kinetics of the Pull Phase of Lifting

摘要

A comparison was made between measured and modeled hand forces applied to theload during two handed floor to knuckle lifting tasks in the sagittal plane, to determine if dynamic biomechanical models should be supplemented with additional information to accurately model hand forces. For the middle portion of the lift, the carry phase, measured and modeled hand forces were comparable. They deviated substantially at the beginning of the lift, the pull phase, and at the ending, the placement phase, of the lift. A steep spike during the pull phase of the lift was exhibited by the measured hand forces which was not evident in the modeled hand forces. The peak force sometimes occurred just before liftoff. The peak compression and shear forces at the low back calculated with input of measured hand forces were greater than peak modeled low back forces for the normal, comfortable speed of lift, and significantly greater for the fast speed of lift. For most lifting tasks, the steep peak at the pull phase in compression and shear forces at the low back plotted over the duration of the lifting tasks was also evident. The authors conclude that the dynamic biomechanical model should be supplemented with a static model of the pull phase of the lift to more accurately represent the peaking of actual hand forces and the resulting compression and shear forces at the low back.