Background and context: One basic physiologic response to spinal manipulation (SM) is a transient decrease in motoneuronal activity, as assessed by the Hoffmann reflex (H-reflex) technique. However, questions of appropriate control procedures when using the H-reflex technique to study the basic physiologic mechanisms of SM still exist. The identification of appropriate control procedures may allow us to better differentiate among the specific and nonspecific aspects of SM.
Purpose: The purpose of the research was to determine the contributions of postural perturbations on the attenuation of motoneuronal activity following spinal manipulative thrusts and spinal joint preload procedures applied to the lumbar spine.
Study design/setting: H/M(max) ratios, recorded from the gastrocnemius muscle, were measured before and after lumbar spinal procedures. The experimental designs for the laboratory data collection protocols were repeated measures and between-subjects.
Patient sample: The subjects were asymptomatic, young, healthy volunteers.
Outcome measure: H/M(max) ratios recorded from the gastrocnemius muscle.
Methods: In Experiment 1, the administration of prone lumbar procedures involved either manual assist to more fully shear the lumbar zygapophyseal joints or no manual assist. One set of subjects (n=17) received assisted joint preload force and manipulation, whereas a second set of subjects (n=17) received unassisted joint preload force and manipulation. In a second laboratory experiment, one set of subjects (n=10) received a L5-S1 side-posture SM, whereas a second set of subjects (n=10) were just positioned into side-posture.
Results: There was a H/M(max) ratio attenuation of 18.2% after assisted spinal manipulation, whereas H/M(max) ratio attenuation was only 9.5% after unassisted spinal manipulation. Decreases of H/M(max) ratios by 8.5% and 7.5% were observed after assisted and unassisted joint preload forces, respectively. The amount of H/M(max) ratio attenuation was significantly greater immediately after the L5-S1 SM procedure (28.4%) as compared with a side-posture positioning maneuver (15.3%).
Conclusion: SM may provide procedure-specific sensory input that appears to vary, based upon the various types of vertebral loading applied to the lumbar spine.