Manual materials handling capabilities in non-standard postures

Abstract

Research efforts to establish manual materials handling (MMH) capabilities of individuals and populations have been conducted for many years. Most of the previous efforts have explored 'standard postures', utilizing two-handed, symmetric, sagittal plane MMH using unrestricted postures. Recognizing that many industrial MMH activities do not utilize 'standard postures', recent research projects have explored psychophysically determined MMH capacities in a variety of non-standard postures. Among the non-standard postures examined were: twisting while lifting or lowering, lifting and lowering from lying, sitting, kneeling, and squatting positions, and carrying loads under conditions of constricted ceiling heights. This paper presents the results of a series of previous research efforts at Texas Tech University. The results are presented in the form of population capabilities of both males and females for 99 MMH tasks using 'non-standard postures'. The data tables contain means and standard deviations of the data, as well as percentile distributions for the subject populations. Sample sizes for the experimental populations ranged from 45 to 50 subjects of each sex in the first three experiments to 20 subjects of each sex in the fourth set of experiments.

Effect of different multipliers and their interactions during manual lifting operations

“…Several studies (Snook and Ciriello, 1991;Smith et al, 1992) showed that with increase in vertical lifting distance the maximum acceptable weight (MAW) value was decreased. This is due to the fact that the work-stress factor positively increases with this vertical lifting distance.…”

Workplace Risk Factors and Occupational Musculoskeletal Disorders, Part 1: A Review of Biomechanical and Psychophysical Research on Risk Factors Associated with Low-Back Pain

“…The initial Liberty Mutual study focused on lifting with maximum acceptable weight (MAW) being the dependent variable of primary interest. Subsequent studies at Liberty Mutual and other research labs have examined materials handling activities such as carrying, pushing, pulling, and lowering, (16)(17)(18)(19)(20)(21)(22)(23) and more recently, repetitive hand motions. (24)(25)(26) The psychophysical approach also has been used to evaluate the stressfulness of work by having subjects in a laboratory or workers on the job rate their perceptions of the intensity of work effort and/or their perceptions of discomfort.…”

A Prospective Field Study of the Relationship of Potential Occupational Risk Factors with Occupational Injury/Illness

“…The number of trunk flexions and twists, trunk motions, time spent in static trunk flexion, number of knee flexions, two measures of shoulder flexion, time spent in static shoulder flexion, and the number of shoulder abductions per hour were averaged for each job classification. These body motions were gathered in an effort to capture identified, potentially hazardous postures (3,18) including horizontal distance away from the body, (3) degree of trunk flexion, (7) trunk asymmetry, (5) static trunk flexion, (49) and lifts overhead. (6) …”

“…(7,47) Trunk twisting may increase spinal shear forces, is associated with decreased maximal acceptable weight of lift, and has been associated with lowback pain. (5,48) Finally, static, bent-over work postures also have been related to occupational low-back pain. (46,49) …”

“…Performing lifts from floor level, lifts with loads away from the body, asymmetrical lifts, or lifts overhead can create increased musculoskeletal stressors and/or decrease maximal acceptable weights of lift. (3,(5)(6)(7) Overexertion while maneuvering materials is the leading cause of disabling events or exposures. (8) Approximately 67% of overexertion claims involved lifting.…”