Effect of task factors on the heart rate recovery time in a lifting task

Abstract

BACKGROUND: There is an extensive body of research reviewing the effect of task factors on the Maximum Acceptable Weight of Lift (MAWL) or heart beats elevation as a result of a manual material handling task. However, there are now studies that investigate the effect of task factors on the heart rate recovery time (HRR). OBJECTIVE: The purpose of the study was twofold: (1) to determine the HRR for a series of lifting tasks based on the activity heart rate and by using a set of task variables, (2) to compare the effect of three task factors on the HRR following a lifting task. METHODS: This research was constituted of capturing the duration that heart rate needs to get to a steady state following a lifting task, along with conducting the survey of perceived exertion (Borg). Three independent variables of this study (task-factors) were weight of the lift (10 and 20 kg), frequency of the lift (6 and 9 lifts per minute), and the duration of the lift (5 and 10 minutes). Given the possible treatment combinations, a total of 8 treatments was obtained. Twenty-four university male students performed the lifting tasks in a between-subject design. Each participant performed one treatment by lifting a box from knuckle to shoulder height at a certain frequency, duration and weight. All eight treatments were equally replicated with three observations per treatment group. RESULTS: Increasing weight and frequency of the lift significantly increased the HRR (respectively by 37% and 34%), while the HRR had a slight decrease when duration was doubled (approximately -2.7%). Weight of the lift was the only factor led to a significant change in the perceived difficulty of the task among participants (approximately 20%). CONCLUSIONS: Among main factors, frequency and weight of the lift had a significant effect on the HRR (p-values < 0.1). Among the interaction effects, the interaction of frequency and duration had a significant effect on the HRR. The only factor that had a significant effect on the Borg-rating was weight of the lift (p-value < 0.1).