Design: Cross-sectional with repeated measures on footwear conditions for patients with musculoskeletal disorders. Single-blind of investigator for footwear conditions.
Setting: Research Laboratory.
Methods: The participants were 12 asymptomatic individuals and 11 patients with musculoskeletal disorders. In the prone and standing positions, H/M recruitment profiles were generated with subjects wearing their aerobic shoes. The subjects rested prone on a treatment table with their feet resting on foot plates. During quiet standing trials, subjects balanced equally on both feet while maintaining a relaxed posture and lightly grasping a hand support at hip level to minimize the influence of postural sway and fatigue. The patients were tested with and without their orthotics inserted into their aerobic shoes. The tibial nerve H-reflex methodology was used to record M-wave and H-reflex responses from the gastrocnemius muscle of the right leg. The Hmax/Mmax ratio was calculated from the recruitment profile in each test position.
Results: The amount of H-reflex inhibition for the prone position to quiet standing did not systematically increase with the orthotic intervention (12.7%) as compared to the patient's normal shoe condition (13.2%). Regardless of footwear condition, the amount of H-reflex inhibition from the prone position to quiet standing was similar to the effect observed in the asymptomatic individuals (13.4%). Among the patients with musculoskeletal disorders, subject-specific variations in the amount of H-reflex inhibition from the prone position to quiet standing were significantly different from zero, between the two footwear conditions (5.7%; t10 = 4.54).
Conclusion: Altering sensory feedback signals from the plantar surface of the foot with an orthotic intervention modified sensorimotor integration mechanisms in a subject-specific manner. In agreement with biomechanics research and neuromuscular concepts for the benefits of orthotics, sensorimotor integration mechanisms may be different for each subject-shoe-insert condition.
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