Self-Paced High Frequency Lifting of Light Loads

A study was designed to psychophysically examine the maximum acceptable frequency of lifting for light loads. Twelve male subjects participated in the experiment in which they lifted boxes weighing either 0.7 kg or 4.5 kg from an initial height of 0.76 m to a final height of 1.27 m. Therefore, the lifting was primarily in the knuckle to shoulder height range, involving arm lifting and very little lifting of body weight. The task duration was one hour and subjects were allowed and encouraged to make as many adjustments as they felt necessary to arrive at their maximum acceptable frequency of lift. Cardboard boxes, (28 cm high by 30 cm wide by 25 cm deep) without handles, were used as lifting containers. For the 0.7 kg load, selected frequencies ranged from a low of 22 lifts per minute to a high of 40 lifts per minute. For the 4.5 kg load, the maximum acceptable frequencies ranged from 14 to 31 lifts per minute. Only two of the twelve subjects selected frequencies of 15 or lower for the 4.5 kg load and none selected a frequency of less than 22 lifts per minute for the 0.7 kg load.