A psychophysical study of high-frequency lifting

Date

1993-08

Journal Title

Journal ISSN

Volume Title

Publisher

Texas Tech University

Abstract

Ergonomic research on worker lifting in industry has most often concentrated on the maximum amount of weight that a worker is capable of and willing to lift in a given situation. However, in many industrial or service manual material handling situations the key question is not how much weight per lift a worker can handle but how frequently the worker is capable of lifting a light weight without strain or overexertion. Such situations often involve the intermittent handling of very light weights for relatively short periods of time. The overall objective of the study was to investigate subject physiological and psychophysical response to the standing arm lift of light weights.

A psychophysical experiment with physiological data collection was designed to utilize two conditions of weight (1.5 lb and 10 lb) lifted from a shelf height of 30 inches to a shelf height of 50 inches (roughly knuckle-to-shoulder height). In this experiment the lift weights were given task variables and the frequency of lift was the dependent variable controlled by the subject. The subjects were instructed to work as hard as they could for a one-hour work session without overexerting themselves and called out adjustments (raise or lower) to a beeper-metronome which provided an audible signal to cue the subjects to lift. Heart rate and oxygen consultation data was collected during the last 15 minutes of the hour-long sessions. Two replications were performed for each weight. After the paced sessions were completed, each subject repeated one session for each of the weights with the same instructions only without the beeper-metronome to provide a cue. The subjects were instructed to maintain a steady pace, working as hard as they could, and relying only on their own internal impressions of pace to cue their lifts.

The subjects were selected and classified according to body weight and somatotype or body-build. A nested-factorial analysis of variance was performed to evaluate the effects of body weight and lift weight on the chosen frequencies, heart rate, oxygen consumption and percentages of various aerobic capacities utilized. Correlation analysis was utilized to investigate the effects of somatotype on experimental performance.

The mean frequencies of lift identified in the experiment were 31.21 lifts per minute and 23.50 lifts per minute for the 1.5 lb and 10 lb lift weights, respectively. Such frequencies of lift are much higher than lift frequencies studied as task variables in other psychophysical studies of lifting. 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. Significant differences also existed between the subject body weight categories. There were no significant frequency or heart rate differences between the paced and unpaced experimental sessions. Somatotype was not shown to be a significant correlate of lift frequency in the 1.5 lb weight condition but appeared to be so in the 10 lb weight condition.

Overall, the study provided insight into human psychophysical and physiological responses to the lifting of light weights. Furthermore, the study suggests guidelines for such work.

Description

Keywords

Lifting and carrying

Citation