Neuromuscular neutral zones sensitivity to lumbar displacement rate.
Eversull-E; Solomonow-M; Zhou-B; Baratta-RV; Zhu-M
Clin Biomech 2001 Feb; 16(2):102-113
Objectives. To determine the displacement and tension thresholds (developed during anterior lumbar flexion) which trigger reflexive muscular activity in the multifidus muscles; their variability with the velocity of flexion; and the pattern of threshold variability across the lumbar spine. Design. An in-vivo study of the feline during passive lumbar flexion applied via the L-4/5 supraspinous ligament. Method. EMG from six pairs of intramuscular electrodes inserted in the L-1/2 to L-6/7 multifidus muscles was recorded while the lumbar spine was passively flexed to 75% of the physiological strain of the supraspinous ligament at rates of 17-100%/s. Three-dimensional models of tension threshold, flexion rate and lumbar levels were developed from the experimental data. Results. Displacement and tension thresholds were the lowest at the fastest flexion rate and gradually increased as flexion rates decreased. Electromyographic activity was detected at low thresholds at the center of the flexion and at gradually increasing thresholds at higher and lower lumbar segments. Conclusion. Multifidus reflexive muscular activity, which stabilize the spine, is triggered at a displacement and tension thresholds of 5-15% of the physiological range. Earlier activation of muscular activity occurs as the velocity of flexion increases. Earlier activation also occurs near the center of flexion.
Muscles; Muscular-disorders; In-vivo-study; Animal-studies; Animals; Laboratory-animals; Spinal-cord; Tension; Back-injuries; Spasms; Musculoskeletal-system; Musculoskeletal-system-disorders
Bioengineering Laboratory, Department of Orthopaedic Surgery, Louisiana State University Health Sciences Center, Suite 400, 2025 Gravier Street, New Orleans, LA 70112
Disease and Injury: Low Back Disorders
Louisiana State University, Health Sciences Center, New Orleans, Louisiana