The effects of a single session of chiropractic care on strength, cortical drive, and spinal excitability in stroke patients.
Scientific Reports 2019
Holt K, Niazi IK, Nedegaard RW, et al.
A research team based out of the New Zealand College of Chiropractic who have been publishing a great deal on the neurophysiologic impact of chiropractic on the brain did an investigation on the impact of chiropractic adjustments on patients who have previously suffered a stroke.
The study was set up as a randomized controlled crossover trial of 12 patients with a previous history of stroke. For the first week, half the patients received an adjustment while the other half had a control maneuver of just moving the body around. Seven days later, the groups switched with the control group getting an adjustment and the intervention group getting a control.
The authors tested patients who suffered weakness in their ability to plantar flex post stroke and tested their strength on plantar flexion pre and post adjustment.
They also wanted to know if there were increases in strength, were they likely tied to a local spinal cord mechanism, or did the strength change come from the brain. To do that, they used electrodiagnostic testing to measure things called the H-Reflex and the V-Wave.
The H-reflex uses an electrical stimulation of a peripheral nerve (the tibial nerve in this case) during a sub-maximal contraction to measure excitability in the spinal motorneuron pools (influenced at the spinal cord level)
The V-Wave uses electrical stimulation during maximal contraction to measure recruitment of additional neuronal pools which is an indicator of cortical drive (influenced by the brain)
If you want to get into the weeds on these tests, you can read this paper here.
There were large and significant changes in maximum contraction of plantar flexion post adjustment while the control group showed a decrease in strength.
As far as the electrical diagnostic testing, the chiropractic group showed large and significant changes in the V-wave indicating that the strength change was likely from a brain mechanism (cortical drive).
For the H-Reflex slight change in the adjustment group that was not significant. There was also a slight decrease in V-wave change in the control group that was also not significant.