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Effects of static flexion-relaxation on paraspinal reflex behavior
Kevin P Granata1, Ellen Rogers, Kevin Moorhouse
1Musculoskeletal Biomechanics Laboratories, Department of Engineering Science and Mechanics, School of Biomedical Engineering and Science, Virginia Polytechnic Institute and State University, 219 Norris Hall (0219), Blacksburg, VA 24061, USA. granata@vt.edu
Clinical Biomechanics (Bristol, Avon)
|November 30, 2004
Summary
Prolonged static trunk flexion alters paraspinal muscle reflexes, potentially increasing low-back pain risk. Gender significantly influences these neuromuscular responses, highlighting the need for personalized risk assessments.
Area of Science:
- Biomedical Engineering
- Kinesiology
- Musculoskeletal Research
Background:
- Static trunk flexion and altered trunk muscle reflexes are linked to increased low-back pain risk.
- Animal studies suggest passive tissue strain in spinal ligaments affects reflex responses.
- Limited human data exists on trunk extensor muscle reflex changes after static flexion loading.
Purpose of the Study:
- To investigate the human reflex response of trunk extensor muscles after static flexion-relaxation loading.
- To determine if prolonged static trunk flexion affects paraspinal muscle reflex gain.
- To explore potential mechanisms linking flexed posture work to low-back pain.
Main Methods:
- Eighteen subjects maintained static lumbar flexion for 15 minutes.
- Paraspinal muscle reflexes were elicited using pseudorandom stochastic force disturbances before and after the protocol.
- Electromyography (EMG) and time-domain deconvolution analyses were used to compute reflex gain.
Main Results:
- A trend toward increased reflex gain was observed after the flexion-relaxation period (P < 0.055).
- Reflex gain increased with trunk extension exertion (P < 0.021).
- Significant gender differences in reflex gain were identified (P < 0.01).
Conclusions:
- Extended periods of trunk flexion in occupational activities alter paraspinal muscle reflex behavior.
- These changes suggest a mechanism by which flexed posture work may contribute to low-back pain.
- Gender-specific differences in neuromuscular behavior necessitate consideration in risk analyses.