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Related Experiment Videos

Lower back muscle forces in pushing and pulling.

K S Lee, D B Chaffin, A M Waikar

    Ergonomics
    |December 1, 1989
    PubMed
    Summary

    A simple two-muscle torso model accurately estimates erector spinae and rectus abdominis muscle forces during pushing and pulling tasks. This biomechanical model shows high correlation with measured myoelectric activity, validating its use for lower back stress analysis.

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    Area of Science:

    • Biomechanics
    • Ergonomics
    • Human Movement Analysis

    Background:

    • Two-dimensional biomechanical models are commonly used to calculate erector spinae and rectus abdominis muscle forces.
    • These forces are critical for estimating compressive forces on the L5/S1 disc, relevant to lower back stress.
    • The accuracy of simplified torso models in dynamic tasks like pushing and pulling requires further investigation.

    Purpose of the Study:

    • To evaluate the efficacy of a simple two-muscle torso model in predicting muscle forces during pushing and pulling.
    • To compare model-predicted muscle forces with myoelectric activity measurements (EMG) in the erector spinae and rectus abdominis.
    • To assess the model's reliability across different postures and task types.

    Main Methods:

    • Six subjects performed trunk and hand pushing and pulling tasks in both erect (hips braced) and free postures.
    • A two-dimensional biomechanical model was used to predict erector spinae and rectus abdominis muscle forces.
    • Surface electromyography (EMG) root-mean-square (rms) values were recorded as a proxy for muscle force.

    Main Results:

    • High correlation (r² = 0.93) was found between predicted muscle forces and measured EMG for trunk pushing and pulling.
    • Excellent correlation (r² = 0.96) was observed for hand pushing and pulling in an erect posture with hips braced.
    • A significantly lower correlation (r² = 0.37) was found for hand pushing and pulling in a free posture.

    Conclusions:

    • A simple two-muscle torso biomechanical model provides a reasonable estimation of erector spinae and rectus abdominis muscle actions during pushing and pulling.
    • The model's accuracy is high in controlled, erect postures but decreases in less constrained, free postures.
    • This validated model can be a useful tool for analyzing lower back stress in specific occupational and biomechanical contexts.

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