Trunk Flexion and Musculoskeletal Stress during Light Assembly Work

in Journal of Applied Biomechanics
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  • 1 University at Buffalo, SUNY
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Mild trunk flexion held during working tasks throughout the day is considered a risk factor for low back pain. Exactly how the duration of these postures impacts the low back musculature during work tasks is not well understood. The objective of this study was to evaluate the effects of the temporal variation of mild trunk flexion and erect standing postures on low back discomfort and muscular fatigue, defined as a decrease in torso extension strength, during a realistic light assembly task. Study participants performed light assembly tasks for 20 minutes while in mild trunk flexion for periods of either 30 or 60 seconds, followed by recovery periods in which they stood erect, for periods of either 15, 30, 60, or 120 sec. Localized muscle discomfort, decreases in torso extension strength, and muscle activity of erector spinae were recorded. Duration of recovery period had a statistically significant effect on localized muscle discomfort of the lower back, upper back, and shoulders. Duration of trunk flexion and recovery time had an interactive effect on decreases in torso extension strength, for which strength decreased with decreasing recovery time and was more pronounced for trunk flexion periods of 60 sec rather than 30 sec. The mean RMS erector spinae muscle activity during mild trunk flexion was approximately 25% of the measured maximum voluntary RMS muscle activity across all conditions. The results suggest that it is the temporal pattern of muscular trunk flexion, and not the total time spent in trunk flexion, that affects localized discomfort and muscular fatigue of the low back.

The authors are with the Dept. of Industrial Engineering, 342 Bell Hall, University at Buffalo, State University of New York, Buffalo, NY 14260-2060.

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