Evaluation of Force Exertion Strategies During Repetitive Lifting/Lowering Tasks Based on Time-Frequency Analysis

This study aimed to evaluate the force exertion strategies during repetitive luggage lifting/lowering tasks based on time-frequency analysis. Right-handed male subjects participated in this experiment and repetitively performed a sequential task including luggage lifting and lowering for 25 times. To vary the workload on the right and left hands, the luggage used in this experiment was designed to enable the modification of the location of additional heavy goods. The experimental conditions included scenarios wherein heavy goods were installed to the right side, center, and left side on the top of the luggage and scenarios without additional heavy goods. In the experiment, the handling force on each hand was measured using two six-axis force-torque sensors at a sampling frequency of approximately 50 Hz. The measured handling forces were analyzed using a short-time Fourier transformation, and the median frequency was calculated. In the scenario where additional heavy goods were installed, the median frequency of handling force on the left hand increased whereas that on the right hand decreased with time. In conclusion, the present study clarified that participants adopted different force exertion strategies with the left and right hands or under experimental conditions and that the applied strategies can be evaluated based on time-frequency analysis.