An Investigation of the Variability in Human Performance during Sagittally Symmetric Lifting Tasks

Several industrial surveillance studies have suggested that variability in the biomechanical requirements of a job could hold significant information with regard to the risk of an individual incurring an occupational low-back injury. This variability may be in the form of variable job demands or in the form of variability in the technique that an individual uses to perform a task. The goal of the current study was to quantify the variability in human performance during sagittally symmetric lifting tasks. In this study, measures of human performance were limited to the three-dimensional kinematics of the lumbar region of the torso and the torque developed about the lumbosacral joint. Subjects were asked to lift a weighted box at a rate of four lifts per minute for three minutes. The lifting tasks in this experiment were defined by combinations of three levels of coupling (poor, fair, and good) and seven levels of load (4.5, 9, 13.5, 18, 22.5, 27, and 31.5 kg). As they performed these lifting activities, th...