Maximum acceptable frequency of light load weight lifting

Although workers who lift with a high frequency in non-standard postures, such as kneeling postures, have a high risk of muscle injuries, researchers have not paid much attention to high frequency lifting of light loads. There are still few data on the acceptable maximum frequency of lifting for light loads, both in standard and non-standard postures. Workers who have to perform high frequency lifting of light loads need to improve their working conditions by reducing repetitive motion or over exertion of their bodies. This study examined the maximum acceptable frequency with which to lift light weights (0.68 kg. and 4.53 kg.) in a standing posture and in a two-knee kneeling posture. The range of the lifts was 0.51 m. in both postures (from 0.76 m. to 1.27 m. in the standing posture and from the floor to 0.51 m. in the two-knee posture). Physiological responses including heart rate and oxygen consumption (VO2) were measured, the energy expenditure demands of the tasks were determined, and energy expenditure equations to describe the data were calculated. This study also measured the metabolic cost of maintaining the two-knee posture in order to calculate the two-knee constant. Subjects were 10 male and 10 female students from Texas Tech University. The results showed that the average two-knee kneeling posture constant was 0.0025 L/kg-min, or 0.0126 kcal/min. Maintaining the two-knee posture required more resting oxygen consumption than did maintaining the standing posture. Gender did not significantly affect resting metabolic cost. In contrast, men and women consumed significantly different amounts of oxygen while lifting the two light weights (0.68 kg. and 4.53 kg.) at their maximum frequency in both the two-knee and standing postures. The mean frequencies with which female and male subjects lifted 0.68 kg. in the standing posture conditions were 25.65 and 29 lifts/min, respectively. The mean frequencies with which female and male subjects lifted 0.68 kg. in the two-knee posture conditions were 22.20 and 20.95 lifts/min, respectively. The mean frequencies with which female and male subjects lifted 4.53 kg. in the standing posture conditions were 18.55 and 19.85 lifts/min, respectively. The mean frequencies with which female and male subjects lifted 4.53 kg. in the two-knee posture conditions were 18.20 and 17.15 lifts/min, respectively. All mean frequencies were within the range described by Ronnholm (1962) and Ronnholm et.al. (1962), which found that the physiologically optimal frequency with which to lift a light weight (one under 10 kg.) was 30 lifts/min. Therefore, a female and male industrial workers of similar ages and in similar health should be able to work at similar rates for a similar duration. Energy expenditure models were developed using the stepwise linear regression technique. The main factors – load weight, frequency, body weight, sex, and lifting posture – were significant at the five percent level. All models developed were tested and validated.