Frontiers in Neuroscience recently published an article that highlighted the links between large muscles in the leg and brain health. It has been reported that the study fundamentally alters brain and nervous system medicine “giving doctors new clues as to why patients with motor neuron disease, multiple sclerosis, spinal muscular atrophy and other neurological diseases often rapidly decline when their movement becomes limited.” . Beyond the ramifications for traditional medicine, the study increases the importance of chiropractic research that also shows the links between the brain and leg muscles.
While the relationship between brain activity (especially cognitive ability) and physical activity is well referenced in literature, the study sought to take a closer look at the effect physical activity might have on neurogenesis and the levels of proliferative progenitor cells in the brain. The study in question was an animal model examining two groups of mice: one group was able to move freely. The other was able to move only the forelimbs, which mimics the effect of being bedridden or in zero gravity.
The differences found between the two groups were quite profound. While it was an animal model, and thus the applications to humans may not be exact, rat/mice models are commonly used as predictors for how certain interventions or situations may apply to humans, and thus the findings are likely to be quite significant. Findings included the following:
- The mice who were fully mobile had far greater proliferating cells in the sub-ventricular zone than the motor deprived animals. In fact, the motor deprived animals had “70% fewer proliferating cells” than the control animals .
- The motor deprived animals also had significantly lower proliferation capability than the fully mobile mice.
- The motor deprived mice also showed lower differentiation and maturation capabilities than the fully mobile mice that could move their hind legs.
- The motor deprived mice showed alterations in cell cycle gene expression. These differences applied specifically to two genes: CDK5 regulatory subunit-associated protein 1 and a cyclin-dependant Kinase 6.
- There was also a significant metabolic alteration between the control group and the experimental group.
All these scientific terms spell out a simple message: a severe reduction in movement or gravity stimuli “exerts an important effect on the human body, altering the activity of many organs including the brain .” Among the potential changes are “alteration in afferent signalling and feedback information from intramuscular receptors, to the cerebral cortex, due to a modification of the reflex organisation in hindlimb muscle groups [3, in 2]. The researchers also noted that prolonged limb suspension (as seen in bed rest) induces nervous system plastic properties in humans, and changes in the memory function, spatial learning and protein expression changes in mice.
Essentially, this means that when we reduce exercise (especially in our lower limbs), we compromise neurological health, making it difficult for our body to produce new neural cells which can help us adapt and cope with stress. We also lower the amount of oxygen in the body “which creates an anaerobic environment and alters metabolism ” which then alters some genes which are important for the health of our mitochondria.
“It is no accident that we are meant to be active: to walk, run, crouch to sit, and use our leg muscles to lift. Neurological health is not a one-way street with the brain telling the muscles ‘lift’, ‘walk’, and so on” said Adami 
“Our study supports the notion that people who are unable to do load-bearing exercises — such as patients who are bed-ridden, or even astronauts on extended travel — not only lose muscle mass, but their body chemistry is altered at the cellular level and even their nervous system is adversely impacted,” lead researcher, Dr. Raffaella Adami, was quoted as saying .
Researchers also noted neurotransmitter changes involving glutamate receptors, and the concentration of serotonin, dopamine, GABA and epinephrine in rats, and pointed to other work that demonstrated inhibition of bone formation . These findings are all significant, making it obvious how traditional medicine needs to change in order to support brain health (especially in conditions like motor neurone disease and multiple sclerosis.) But it also shines a light on the importance of exercise in general health. The more we work the muscles in our legs, the more our brain can produce new cells.
The chiropractic leg muscle link
Beyond these initial findings, the study appears to link seamlessly with chiropractic research showing greater muscle strength and less fatigue (to the leg muscles) once study participants were checked and adjusted [4, 5].
If leg muscle strength is important in brain health according to Adami et al, then the fact that the chiropractic adjustment has been found to increase participants to perform maximal leg contractions (with less fatigue over time) is a significant finding. Yes it does represent a circular effect: we boost the brains ability to drive muscles in the leg, and the use of leg muscles boosts the brains ability to create new nerve cells and maintain health throughout the body.
Together, the two studies illustrate the regenerative and mutually beneficial power of the innate intelligence that drives brain and body.
With neurological diseases representing a growing concern as the population ages, these two pieces of research (when read together) provide a powerful impetus to get checked and get moving. We often say that the aim of chiropractic is to add years to life and life to years. Now we can see one mechanism that explains how that might work.
- Staff Writer, Frontiers in Neuroscience (2018), “Leg Exercise is Critical to Brain and Nervous System Health,” Technology Networks | Neuroscience news and Research, https://www.technologynetworks.com/neuroscience/news/leg-exercise-is-critical-to-brain-and-nervous-system-health-304388?fbclid=IwAR283f_BVQCtzRUQ90qFb26Y7Z49FsLx_a9qZwB78uxvgwP7HN9_oHuM_QM#.XGBdYjHkGJM.facebook retrieved 11 February 2019
- Adami, R., Pagano, J., Colombo, M., Platonova, N., Recchia, D., Chiaramonte, R., … & Bottai, D. (2018). Reduction of movement in neurological diseases: effects on neural stem cells characteristics. Frontiers in Neuroscience, 12, 336. DOI: 3389/fnins.2018.00336
- D’Amelio, F., Fox, R. A., Wu, L. C., Daunton, N. G., and Corcoran, M. L. (1998). Effects of microgravity on muscle and cerebral cortex: a suggested interaction. Space Res. 22, 235–244. doi: 10.1016/S0273-1177(98)80015-X
- Staff Writer, (2016), “Greater Strength, Muscle Function and Less Fatigue,” Australian Spinal Research Foundation (Interview with Heidi Haavik), https://spinalresearch.com.au/research-project-h-reflex-and-v-waves-2/ retrieved 4 February 2019
- Niazi, I.K., Türker, K.S., Flavel, S. et al. Exp Brain Res (2015) 233: 1165. https://doi.org/10.1007/s00221-014-4193-5