A psychophysical study of high-frequency arm lifting

Ergonomics research on worker lifting in industry, and the many tools and methods that have resulted from it, have most often concentrated on the maximum amount of weight that a worker is capable and willing to lift in a given situation. In most psychophysical research on lifting, the frequency is one of a number of controlled variables along with container size, lift range, etc. Most of the relatively few studies that have investigated frequency as the response variable have used relatively heavy loads. In the study reported here, the focus was on the lifting of light weights and the subject acceptance of maximum frequency of lift for a two-handed lifting task. The lift range was set at approximately knuckle to shoulder height and was intended to simulate industrial jobs where the worker is tasked with either loading or unloading relatively light weight items to or from a processing line operation. Twelve college-age male subjects were used. Two conditions of weight, 0.7kg (1.5lb.) and 4.45kg (10lb.) were used and the subject adjusted his frequency of lift by communicating with the researcher, who adjusted a metronome to pace the task. The subjects were instructed to work at as fast a rate as they could for an hour period without becoming overheated, overly tired, out of breath or in pain. Measurements of oxygen consumption and heart rate were taken to supplement the psychophysical measure of lift frequency. Two replications of each weight condition were performed. At the conclusion of the metronome-paced sessions, an additional session for each weight condition was performed where the subject was instructed to lift as fast and consistently as they could with no external cuing device. The mean frequencies of lift identified in the experiment were 31.21 lifts per minute and 23.50 lifts per minute for the 0.7kg and 4.5kg lift weights respectively. The two weight conditions were significantly different from each other in their effects on subject metabolic energy expenditure with the subjects tending to work significantly harder physiologically at the heavier weight.Relevance to industry: The high frequency lifting of light weight objects in industry is very common although it has not received much specific research attention. It was the intent of this study to investigate subject psychophysical and physiological responses to the high frequency arm lifting of light weights in order to give insight into suggested limits for this type of work.