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Shoulder posture and median nerve sliding.
Andrea Julius1, Rebecca Lees, Andrew Dilley
1Department of Physiology, University College London, UK. AJulius@hhnt.org
BMC Musculoskeletal Disorders
|July 30, 2004
Summary
Slumped sitting does not significantly strain the median nerve. However, shoulder protraction reduces median nerve movement, potentially increasing injury risk and upper limb pain.
Area of Science:
- Biomechanics
- Neuroscience
- Anatomy
Background:
- Upper limb pain is often associated with slumped sitting and poor shoulder posture.
- Poor posture may lead to mechanical changes affecting major limb nerves like the median nerve.
Purpose of the Study:
- To determine if slumped sitting components (forward head, trunk flexion, shoulder protraction) cause median nerve stretch.
- To investigate if shoulder protraction restricts normal median nerve movement.
Main Methods:
- High-frequency ultrasound and cross-correlation analysis measured longitudinal median nerve movement during slumped sitting components.
- Nerve movement in the arm during contralateral neck side flexion assessed the effects of shoulder protraction.
Main Results:
- Forward head posture and trunk flexion did not significantly move the median nerve.
- Shoulder protraction caused 4.3 mm of median nerve movement (0.7% strain) in the forearm.
- Protraction reduced arm median nerve movement by 60% during neck side flexion compared to neutral.
Conclusions:
- Slumped sitting is unlikely to cause nerve strain sufficient to alter nerve function.
- Shoulder protraction may risk median nerve injury by reducing its movement through the shoulder region.
- Altered nerve dynamics and local blood supply changes due to protracted shoulders can increase upper quadrant pain risk.