Abstract
Musculoskeletal models may enhance our understanding of the dynamic loading of the joints during manual material handling. This study used state-of-the-art musculoskeletal models to determine the effects of load mass, asymmetry angle, horizontal location and deposit height on the dynamic loading of the knees, shoulders and lumbar spine during lifting. Recommended weight limits and lifting indices were also calculated using the NIOSH lifting equation. Based on 1832 lifts from 22 subjects, we found that load mass had the most substantial effect on L5-S1 compression. Increments in asymmetry led to large increases in mediolateral shear, while load mass and asymmetry had significant effects on anteroposterior shear. Increased deposit height led to higher shoulder forces, while the horizontal location mostly affected the forces in the knees and shoulders. These results generally support the findings of previous research, but notable differences in the trends and magnitudes of the estimated forces were observed.
Highlights
Manual material handling (MMH) constitute a substantial proportion of the work performed in many industries, such as manufacturing, construction and retail (Heran-Le Roy et al, 1999)
Sixteen trials were either missing or excluded: four trials of horizontal location (HL)-35 and one trial of deposit height (DH)-30 were missing for subject 22 and 7, respectively, while four trials of DH-150 were missing for subject 12, as the subject was not able to reach this shelf height
This study provided a detailed analysis of the dynamic peak forces in the major joints during MMH with varying loads, asymmetry, start and end locations based on state-of-the-art musculoskeletal models
Summary
Manual material handling (MMH) constitute a substantial proportion of the work performed in many industries, such as manufacturing, construction and retail (Heran-Le Roy et al, 1999). MMH pose a substantial burden on society, both in terms of the human and economic costs (Dempsey, 1998; Dempsey and Hashemi, 1999) For these reasons, substantial efforts have been made to understand how the body is loaded during MMH and how some loads may increase the risk of injury to the involved joints. The NIOSH guidelines were later revised to account for hand coupling and asym metrical lifting (Waters et al, 1993, 1994). This version has since been shown to be a reasonable predictor of injury risk to the lower back
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