REFLEX RESPONSES ASSOCIATED WITH MANIPULATIVE TREATMENTS ON THE THORACIC SPINE - A PILOT-STUDY

Objective: To test systematically if spinal manipulative treatments (S MT) and the audible release associated with SMT cause activation of sp inal muscles. Design: Experimental pilot study. Setting: Human Perform ance Laboratory, The University of Calgary. Participants: One male and one female asymptomatic volunteer. Intervention: Slow and fast SMTs t o the left transverse process of thoracic vertebrae using a reinforced hypothenar contact. The treatment forces were directed in a posterior -to-anterior direction with the subjects in a prone position. Main Out come Measures: Forces applied by the chiropractor during SMT. Measurem ents of the audible release using skin-mounted accelerometers. Electro myographical activity of selected spinal muscles. Results: Electromyog raphical (EMG) activity was observed consistently 50-100 msec after th e onset of each of the fast SMTs, whether the treatment resulted in an audible release or not; for slow SMTs, there was never any visible el ectromyographical activity of the target muscles, whether the treatmen t resulted in an audible release or not. Conclusion: The results of th is study suggest that fast treatment thrusts elicit muscle activation, whereas slow force application does not. The timing of the onset of t he EMG response suggests that activation may be produced by a reflex r esponse originating in the muscle spindles. It also appears that the a udible release does not (by itself) evoke muscle activation or a joint proprioceptive reflex response as has been speculated in the literatu re.