Psychophysically Determined Asymmetrical Lifting Capabilities for Different Frequencies and Containers

Abstract

Back injuries to the lifters caused by lifting remain a common occurrence not only in developed countries, but also in developing and undeveloped countries. Asymmetric lifting task, combining lifting, bending and twisting motions of the torso, is more harmful to back spine than symmetric lifting task. Snook and Irvin 1) first developed the psychophysical approach to determine human maximum acceptable weight of lifting (MAWL) for preventing lifters from sustaining back injuries, and this approach has been adopted in various lifting conditions. Ciriello et al.2) indicated that the psychophysically determined MAWL data could be applied to a general work day for task frequencies of 4.3 lifts/min or lower.Very few papers reported the container effects on psychophysically determined MAWL, especially for asymmetric lifting. This study examined the effects of lifting frequency and container on psychophysically determined 4-h MAWL for 90-degree asymmetric lifting tasks from floor to knuckle height (approximately 74 cm). Additionally, this study compared the MAWL data with the recommended weight limits derived from the revised NIOSH lifting equation 3) . It is hoped that these MAWL data can help designing asymmetric lifting jobs for reducing the severity and frequency of overexertion injuries and improving productivity.Ten young healthy and lift-experienced males gave their written consent form for this experiment. Their mean (SD) age was 20.0 (0.5) yr, weight was 62.7 (8.0) kg, and height was 170.0 (4.3) cm.A two-factor factorial design was used to examine the effects of lifting frequency and container on participants' MAWL capability in asymmetrical lifting tasks. Three lifting frequencies, 1 lift/min, 2 lifts/min and 4 lifts/min, and three containers (length*width*height), 70 × 35 × 15 cm, 50 × 50 × 15 cm and 50 × 35 × 15 cm were selected. The three containers were designed for examining the effects of

Effect of safety shoes type, lifting frequency, and ambient temperature on subject's MAWL and physiological responses

“…Increasing lifting frequency from 1 lift/ min to 5 lifts/min resulted in 14% reduction in mean weight lifted compared to 47.1% found by Hafez (1984), and Hafez and Ayoub (1991), 23.5% found by Ramadan (1988), 16.1% found by Lee (2005) and 12.7% found by Singh et al (2012). The reason that Hafez (1984) has much higher reductions in MAWL than this study could be because the differences exist in the population employed, where in our study participants are used to and can tolerate more heat at work.…”

Evaluation of the Impact of the Revised National Institute for Occupational Safety and Health Lifting Equation

“…The maximal acceptable weight (15% reduction from condition without lift asymmetry) for a lifting task with a 90° asymmetry was about one half of the RWL (30% reduction) determined by the RNLE (Han et al, 2005). These studies concluded that the RWL was more conservative in comparison with the results from the psychophysical studies (Han et al, 2005; Lee, 2005; Wu, 2003). …”

Psychophysically determining the maximum acceptable weight of lift for polypropylene laminated bags

“…The assumption of psychophysical stress as an integration of physiological and biomechanical stress has been studied by several researchers1, 5, 8, 12 ) . Specific instructions were given for the MAWL determination to adjust the weight of the bag by adding or subtracting sand to the maximum amount that they could lift comfortably (i.e., without straining themselves) for an 8-h workday in an assigned task combination.…”

“…The maximum acceptable weight of lift (MAWL) is one of the most widely used approaches for representing a person’s lifting capacity and is thus employed to design appropriate jobs1 ) . When lifting, the weight and its distribution, shape, stiffness, and handles are object characteristics that must be considered in the design of lifting tasks2, 3 ) .…”