Chiropractic care is commonly thought to have a beneficial effect on the functioning of the human body by affecting the nervous system. Evidence indicates that chiropractic adjustments result in plastic changes in sensorimotor integration within the central nervous system in human participants, particularly within the prefrontal cortex. Adjustments appear to alter the net excitability of the low-threshold motor units, increase cortical drive, and prevent fatigue (see this blog). This same group of researchers have more recently found an increase cortical drive to upper and lower extremity muscles following manipulation as measured by motor evoked potential. The researchers suggested the effects were due to descending cortical drive and could not be explained by changes at the level of the spinal cord (although they can’t rule that out completely). Two experiments were conducted. In experiment one, transcranial magnetic stimulation input–output (TMS I/O) curves for an upper limb muscle (abductor pollicus brevis; APB) were recorded, along with F waves prior to and after either spinal manipulation or a control intervention for the same subjects on two different days. During these two separate days, lower limb TMS I/O curves and movement related cortical potentials (MRCPs) were recorded from tibialis anterior muscle (TA) before and after spinal manipulation. Spinal manipulation resulted in a 54.5% ± 93.1% increase in maximum motor evoked potential (MEPmax) for APB and a 44.6% ± 69.6% increase in MEPmax for TA. They conclude that “Spinal manipulation may therefore be indicated for the patients who have lost tonus of their muscle and or are recovering from muscle degrading dysfunctions such as stroke or orthopaedic operations. These results may also be of interest to sports performers. We suggest these findings should be followed up in the relevant populations.”
Reference: Haavik H, Niazi IK, Jochumsen M, Sherwin D, Flavel S, Türker KS. Impact of Spinal Manipulation on Cortical Drive to Upper and Lower Limb Muscles. Brain Sci. 2016 Dec 23;7(1).