The brain represents only about 2 percent of most people’s body weight, yet it accounts for about 20 percent of the body’s total energy usage—about 10 times more than would be expected. When the brain is fully working, it uses more energy per unit of tissue weight than a fully exercising quadricep. In fact, the human brain cannot simultaneously activate more than 2 percent of its neurons at any one time. More than this, and the glucose supply becomes so quickly exhausted that you will faint.
Consider the following statistics. The three requirements for human life are food, drink, and fresh air. But their effects on survival have very different timelines. You can live for 30 days or so without food, and you can go for a week or so without drinking water. Your brain, however, is so active that it cannot go without oxygen for more than 5 minutes without risking serious and permanent damage. Toxic electrons over-accumulate because the blood can’t deliver enough oxygen sponges.
Exercise does not provide the oxygen and the food. It provides your body greater access to the oxygen and the food. How this works is easy to understand.
Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School
The more you exercise, the more tissues you can feed and the more toxic waste you can remove. This happens all over the body. That’s why exercise improves the performance of most human functions.
The same happens in the human brain. Imaging studies have shown that exercise literally increases blood volume in a region of the brain called the dentate gyrus. That’s a big deal. The dentate gyrus is a vital constituent of the hippocampus, a region deeply involved in memory formation.
At the molecular level, early studies indicate that exercise also stimulates one of the brain’s most powerful growth factors, BDNF. That stands for Brain Derived Neurotrophic Factor, and it aids in the development of healthy tissue. BDNF exerts a fertilizer-like growth effect on certain neurons in the brain. The protein keeps existing neurons young and healthy, rendering them much more willing to connect with one another. It also encourages neurogenesis, the formation of new cells in the brain. The cells most sensitive to this are in the hippocampus, inside the very regions deeply involved in human cognition. Exercise increases the level of usable BDNF inside those cells. The more you exercise, the more fertilizer you create—at least, if you are a laboratory animal.
Recall that our evolutionary ancestors were used to walking up to 12 miles per day. This means that our brains were supported for most of our evolutionary history by Olympic-caliber bodies.
Exercise makes your muscles and bones stronger, for example, and improves your strength and balance. It helps regulate your appetite, changes your blood lipid profile, reduces your risk for more than a dozen types of cancer, improves the immune system, and buffers against the toxic effects of stress (see Chapter 8). By enriching your cardiovascular system, exercise decreases your risk for heart disease, stroke, and diabetes.
The idea of integrating exercise into the workday may sound foreign, but it’s not difficult. I put a treadmill in my own office, and I now take regular breaks filled not with coffee but with exercise. I even constructed a small structure upon which my laptop fits so I can write email while I exercise. At first, it was difficult to adapt to such a strange hybrid activity. It took a whopping 15 minutes to become fully functional typing on my laptop while walking 1.8 miles per hour.
Brain Rules: 12 Principles for Surviving and Thriving at Work, Home, and School by John Medina
“We all are learning, modifying, or destroying ideas all the time. Rapid destruction of your ideas when the time is right is one of the most valuable qualities you can acquire. You must force yourself to consider arguments on the other side.
— Charles T. Munger”
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