We are constantly reminded of how exercise affects positively our physiology as well as our esthetics, and how important it is to stay physically active throughout life to age well. And although these considerations have real value, I think it is a bit limited.
Indeed, we are now starting to realize, thank to a constant progress of science, that our body is an integrated system, and that no action, or influence imposed on our body (understand « body » as a whole, not just the bony/fleshy mechanical envelope) wether external or internal, can be looked at from a restricted and limited point of view, and that for an actual response to a given stimulus to occur, the entire human mechanism is put in motion in a holistic way.
Let me illustrate this with an example related to health and fitness :
If John wants bigger biceps (endurance athletes/enthusiasts please stay with me, this concerns you also, just think of John as a triathlete getting ready for an IronMan run), he is going to go to the gym and engage in a particular routine that will focus on stimulating his biceps, and hopefully, he will end up with bigger guns… But the reality of what is happening isn’t limited to his biceps brachii muscles. A host of endocrine, nervous, muscular, conscious and unconscious reactions are going to occur to allow for his biceps to be trained and later on, if the adequate anabolic environment is provided, grow.
This was a lengthy introduction but I think this point needed to be made : Whatever your goals or your speciality in life, even if those are more of an intellectual nature, you should ALWAYS look at your body as an intricate, interrelated system and how this relates to your daily performances.
To illustrate this essential fact, and to give substance to my allegations, I am going to introduce you to a fact that might be new to you : Physical activity has the potential to increase cognitive functions, orientation and improve overall emotional state.
The first thing that is crucial to understand this, is that the very same part of the brain is responsible for these three essential functions : The hippocampus.
The hippocampus is a small part of our brain located in the temporal lobe, and its very interesting propriety is that it is one of the only two parts of the brain where neurogenesis (birth of new neurons or brain cells) keeps on happening after birth, throughout our entire life, in order to allow us to continuously learn and master new skills as well as to be emotionally responsive.
Another fact worth mentioning to illustrate the importance of the hippocampus, is that it is the first part of the brain to suffer from Alzheimer’s disease and other forms of dementia.
The two factors that are linked with better brain function and exercise are increased neurogenesis and increased angiogenesis (creation of new blood vessels).
Indeed, more neurons being born increases potential cognition and neural survival, and better vascularization of the brain results in increased cerebral blood volume which ensures better supply of oxygen and nutrient to the neurons for an overall better functioning brain.
But what is the exact pathway between exercise and these two reactions (neurogenesis and angiogenesis) ?
Well, the main growth factors responsible are IGF-1 (insulin like growth factor one) for both neuro and angio genesis, and BDNF (Brain derived neurotrophic factor) when it comes to neurogenesis only.
IGF-1 is a peptide hormone, secreted by the liver, that is responsible for many growth mechanism in the body.
BDNF is a protein synthesized in the brain, that is responsible for neural survival and synaptic plasticity.
Lets talk briefly about BDNF first, since its effects are not as potent and crucial as IGF-1’s : Firstly, IGF-1 and BDNF are interdependent because IGF-1, when present in the brain, strongly stimulates the synthesis of BDNF, and BDNF, as explained above, is a protein that stimulates brain cell survival and synaptic plasticity.
And that is really worth our attention : synaptic plasticity is the increase in strength of the nervous connection between two neurons. Simply said, BDNF increases the efficiency of communication between neurons.
On another note, BDNF has been found to have an antidepressant effect by stimulating hippocampal size and activity.
But IGF-1 is by far our main player, its benefits and functions are plenty.
First IGF-1 is a growth factor that stimulates the creation of both new neurons and new blood vessels as well as stimulating BDNF synthesis, but it doesn’t stop there : IGF-1 increases spontaneous neural firing (which is the process of sending a nervous signal (action-potential for the nerds…) through the nervous system or to another neuron), as well as cell differentiation. And that, again, deserves all our attention : cell differentiation is the process by which a new, general neuron (without any particular task) is given a particular role/task to accomplish.
I will let you think about how crucial this is when it comes to memory and cognition…
To support the importance of IGF-1 in relation to cognition and brain function from another standpoint : IGF-1 levels were found to be altered in both aging population, and population suffering from different forms of dementia (including Alzheimer’s disease).
Now that we know that IGF-1 is the key to improve brain health, lets look at how exercise comes into play : the first factor is that exercise increases brain uptake of IGF-1, which is good for BDNF synthesis. But more importantly, exercise increases production of IGF-1 through growth hormone secretion.
Indeed, one of the main endocrine response to exercise (aerobic or anaerobic) is the secretion of human growth hormone by the anterior pituitary gland.
Growth hormone is then (8 to 29 hours later) going to stimulate IGF-1 secretion by the liver.
You now have a clear picture of how exercise can affect brain function and efficiency.
From a more factual point of view, two very interesting and conclusive studies were conducted on human subjects :
The first one (2) followed three groups of women (75 years old in average), one group trained for six months in an aerobic fashion (brisk walking), the second in an anaerobic fashion (resistance training) and the third (control) only went through a program of light stretching and relaxation.
The three groups were tested for verbal (learning) and spatial (orientation) memory (two functions directly related to the hippocampus) before and after the study.
The two exercising groups showed a noticeable increase in both tests (spatial and verbal). The third (control) group, on the other hand, showed no real difference between the before and after tests.
The second study (22) which is even more illustrative in my opinion, followed two groups of older people (75 years old in average) of mixed gender for four months.
The first group followed an aerobic training regimen (treadmill walking) four times a week for a total weekly duration of 150 minutes. The second group (control) followed a light stretching regimen and attended several lectures (to account for the impact of intellectual activity).
The researchers screened for increase in cerebral blood volume (sounds familiar ?) and neural connectivity (interaction between neurons) using magnetic resonance imaging (MRI). The actual MRI speaks for itself :
This first image shows the parts of the brain with the highest neural connectivity (the hippocampus being one of them) and we can clearly see in the upper part of the image which shows a summary of the exercising group’s brains, that the connectivity is much more intense than in the control group (lower part of the picture). And if you look at the upper left hand side of the picture, (the side view of the training group) you will notice that you can actually see the horseshoe shape of the hippocampus thriving with neural connectivity (in color redish/yellow).
This chart expresses the perfusion of the hippocampus (blood flow in the hippocampus). The light blue columns
represent the different participants from the training group (the dark blue column is the average) and the red columns represent the control group participants. We can see that the cerebral blood flow in the hippocampus is much greater in the group that exercised for four months.
An other interesting fact that has been demonstrated is that neurogenesis is long lasting only if the newborn cells are actually put to the task and stimulated by an enriched environment (learning)… that resonates pretty well with my introduction doesn’t it ?
So stay active both intellectually and physically and maximize your brain health!
1. Insulin-like growth factor I is required for vessel remodeling in the adult brain by C. Lopez-Lopez, D. LeRoith, and I. Torres-Aleman. Edited by Fred H. Gage, The Salk Institute for Biological Studies, San Diego, CA, and approved May 17, 2004 (received for review January 15, 2004)
2. Physical Activity Improves Verbal and Spatial Memory in Older Adults with Probable Mild Cognitive Impairment: A 6-Month Randomized Controlled Trial by Lindsay S. Nagamatsu, Alison Chan, Jennifer C. Davis, B. Lynn Beattie, Peter Graf, Michelle W. Voss, Devika Sharma, and Teresa Liu-Ambrose. Received 1 November 2012; Accepted 18 January 2013. Academic Editor: Louis Bherer
3. Adult hippocampal neurogenesis and its role in Alzheimer’s disease by Yangling Mu and Fred H Gage. Mu and Gage Molecular Neurodegeneration 2011
4. Adult hippocampal neurogenesis and related neurotrophic factors by Eugene Lee & Hyeon Son 2009. Department of Biochemistry and Molecular Biology, College of Medicine, Hanyang University, Seoul 133-731, Korea
5. The effects of aerobic activity on brain structure by Adam G. Thomas, Andrea Dennis, Peter A. Bandettini, and Heidi Johansen- Berg. Edited by: David L. Wright, Texas A&M University, USA
6. Exercise: a behavioral intervention to enhance brain health and plasticity by Carl W. Cotman and Nicole C. Berchtold. RENDSin Neurosciences Vol. 25 No. 6 June 2002
7. Circulating Insulin-Like Growth Factor I Mediates Exercise-Induced Increases in the Number of New Neurons in the Adult Hippocampus by Jose Luis Trejo, Eva Carro, and Ignacio Torres-Aleman. The Journal of Neuroscience, March 1, 2001
8. Circulating Insulin-Like Growth Factor I Mediates the Protective Effects of Physical Exercise against Brain Insults of Different Etiology and Anatomy by Eva Carro, Jose Luis Trejo, Svetlana Busiguina, and Ignacio Torres-Aleman. The Journal of Neuroscience, August 1, 2001
9. Growth hormone (GH) release during acute and chronic aerobic and resistance exercise by Wideman L., Weltman J., Hartman M. L., Veldhuis J.D. and Weltman A. 2002 : Recent Findings. Sports Medicine 32 (15): 987-1004.
10. Growth Hormone, IGF-1, and testosterone response to resistive exercise by R. R. Kraemer, J. L. Kilgore, G. R. Kraemer and V. Daniel Castracane. Official Journal of the American College of Sports Medicine
11. Insulin’s Effects on Testosterone, Growth Hormone and IGFI Following Resistance Training Jason Dudley
12. Developmental brain research V. 134, issue 1 and 2, 2002, Anderson et al.
13. « A century of Alzheimer disease » by Goedert and Spillantini 2006
22. “Using network science to evaluate exercise-associated brain changes in older adults”, Burdette et al.
23. Brain-Derived Neurotrophic Factor Produces Antidepressant. Effects in Behavioral Models of Depression by Yukihiko Shirayama, Andrew C.-H. Chen, Shin Nakagawa, David S. Russell, and Ronald S. Duman. The Journal of Neuroscience, April 15, 2002, 22(8):3251–3261