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Trunk muscle activities during asymmetric twisting motions
W S Marras1, K G Davis, K P Granata
1Biodynamics Laboratory, Ohio State University, Columbus 43210, USA.
Summary
Trunk twisting in flexed or asymmetric postures increases erector spinae muscle activity and lateral torque, unlike upright twisting. This suggests occupational low back disorder risks may be underestimated by studies using only upright postures.
Area of Science:
- Biomechanics
- Occupational Health
- Musculoskeletal Disorders
Background:
- Axial torso twisting is a risk factor for low back disorders.
- Previous biomechanical studies focused on upright twisting postures.
Purpose of the Study:
- To investigate trunk muscle electromyographic activity during twisting in various postures.
- To compare muscle activation patterns in upright, flexed, and asymmetric trunk postures during twisting exertions.
Main Methods:
- Electromyography of ten trunk muscles was recorded in 12 subjects.
- Subjects performed twisting exertions in upright, flexed, and asymmetric postures.
- Twisting velocity and direction were varied.
Main Results:
- Upright twisting primarily engaged oblique and latissimus dorsi muscles.
- Flexed postures increased erector spinae activity and decreased external oblique activity.
- Asymmetric postures reduced oblique and latissimus dorsi activity while maintaining elevated erector spinae activity, increasing lateral torque.
Conclusions:
- Trunk posture significantly influences trunk muscle activation during twisting.
- Occupational low back disorder risk assessments based solely on upright twisting may underestimate risks in flexed or asymmetric postures.