One of the findings contained in this report was that, just as changes in brain chemistry can affect behavior, it is also true that changes in behavior can affect brain chemistry. For that reason, physical activity is one means to help individuals cope with stressors and adversity as well as enhance somatic health. There is some thinking that aerobic exercise may increase blood flow and oxygen transport to the brain, inducing an elevation in mood state. Studies with animals suggest that permanent structural changes in the brain, including extra blood vessels and nerve endings, can result from regular exercise. Brain wave activity has also been found to be positively altered by exercise training or gains in physical fitness.
Much more research is needed before the influence of exercise on the brain is fully understood.
Epidemiological research among men and women suggests that aerobic physical activities, such as brisk walking and running, have been found to improve mental health for people who report symptoms of anxiety and feelings of sadness, and for those who are diagnosed with some forms of depression. In general, people who are inactive are twice as likely to have symptoms of depression than are most people. Exercise may play a role in the treatment and prevention of depression by normalizing brain concentrations of these chemicals. However, the mental health benefits of physical activity for individuals in relatively good physical and mental health were not as evident, but the studies didn't have sufficient rigor from which to draw unequivocal conclusions. Some researchers have proposed that exercise-induced changes in brain neuroreceptor concentrations of opiates may help to favorably alter mood.