Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding

by Daniel E. Lieberman

familiar. First, physical activity has many direct effects on the brain. One is to flood the brain with mood-altering chemicals. As a reminder, exercise heightens the activity of transmitting molecules in the brain, notably dopamine, serotonin, and norepinephrine.131 These neurotransmitters induce sensations of reward, well-being, arousal, and memory enhancement. Most pharmaceuticals such as SSRIs used to treat depression and anxiety manipulate levels of these neurotransmitters. Exercise also increases levels of other neurotransmitters, glutamate and GABA, that are often depleted in people with depression and anxiety.132 Additional mood-enhancing molecules turned on by exercise include endogenous opioids such as endorphins and endocannabinoids that inhibit pain and produce positive moods.133 Finally, as if this were not enough, remember that physical activity increases levels of BDNF and other growth factors that help maintain brain function. Altogether, regular physical activity alters brain chemistry, enhances electrical activity, and improves brain structure. Among other differences, the brains of more physically active people have enlarged memory regions, more cells, and increased blood supply.134 These evolutionarily normal characteristics may reduce vulnerability to disease.