Effect of Fatigue on Variability of Trunk Kinematics

A repetitive lifting task affords the opportunity for lift-to-lift variability in the lifting strategy and kinematics which can result in changes in the stresses on the tissues of the low back. To quantify the variation of lifting kinematics over time, ten subjects were recruited to perform repetitive lifting of a load equal to 10% of body weight at a rate of six lifts/min for 30 minutes continuously. Trunk kinematic variables were measured in all three planes of motion using the Lumbar Motion Monitor. The variances of the lifting kinematics were compared for the following ten-minute intervals: 0-10 min, 10-20 min, and 20-30 min. Time was found to have a significant impact on the variance of the peak sagittal acceleration, with the variance seen in the first ten minutes exceeding that of the other two time intervals. The downward trend in variation of peak sagittal acceleration implies an initial adjustment as the lifters “settle in” to their preferred lifting strategy.