“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.”