Comparisons with subjective and objective indexes of lifting risk among different combinations of lifting weight and frequency

Abstract

It is evident that the lifting risk increases with both the lifting weight and frequency. However, little is known whether or not different combinations of lifting weight and frequency cause different risks even lifting the same total weight over a period of time. Therefore, the purpose of this study was to investigate the effects of lifting weight and frequency combinations on the lifting risk in the same amount of weight lifted over a period of time. Oxygen consumption, heart rate, and NIOSH’s (US National Institute for Occupational Safety and Health) Lifting Index (LI) were measured and considered as objective risk indexes. The rating of perceived exertion (RPE) was collected as subjective risk index. Sixteen young adults participated in the experiment. Each participant performed four lifting trials with different combinations of lifting weight and frequency, i.e. 12 kg & 2 lift/min, 8 kg & 3 lift/min, 6 kg & 4 lift/min, and 4 kg & 6 lift/min. Each lifting trial last 16 min. Each participant’s oxygen consumption and heart rate were measured during the lifting trial. After each trial, the participant’s RPE and LI were collected. The results indicated the combination of weight and frequency had a significant effect on RPE and LI, but had little effect on oxygen consumption and heart rate. The larger lifting weight accompanied with lower frequency (12 kg & 2 lift/min) had a significant greater RPE and LI than the other three lifting trials. This study provided useful information to determine proper risk predictors for manual lifting tasks with different combinations of object weight and lifting frequency.