Effect of task variables and their interactions in lifting and lowering loads

Abstract

An experiment was designed to study the effect of several task variables on the metabolic energy expenditure and heart rate of individuals performing lifting and lowering tasks. The task variables studied were: load of lift (lower), frequency of lift (lower), height of lift (lower), presence of absence of handles, container height, container width (in the frontal plane) and container length (in the sagittal plane). Four male subjects participated in the experiment. Their oxygen uptake and heart rate were monitored. Various strength measurements were made on the subjects before their participation in the study and after the study was over. The data were analyzed separately for lifting and lowering, using the analysis of variance. Container height did not affect the metabolic energy expenditure or heart rate of the subjects for lifting or lowering activities. Presence or absence of handles did not cause a significant change (alpha greater than or equal to .10) in the physiological responses for lowering tasks. All other task variable effects, however, were significant (alpha less than or equal to .01). A strong first and second order interaction was observed among the task variables. There was a significant increase in the strength (alpha less than or equal to .025) of subjects after performing manual materials handling activities for about seven weeks. A dimensional sensitivity analysis indicated that unit change in box width was more expensive than unit change in box length up to .56 m (22 inches). Beyond this, unit change in box length became critical. The weight/bulk ratio of the object did not affect the physiological responses.