Why exercise protects us from depression.
When our mind wanders into negative thoughts and circles around problems and wrong ideas it is a confused part of our brain, the front/frontal part of the brain, that is in action. But when we play sports it is another part of the brain responsible for movement that is in energy. So the brain during sport sets aside the energy of the frontal lobe. After the sport the frontal area has rested and can have new ideas and thoughts.