Non emotional exercise has a strange effect on dopamine. Heavy aerobic exercise uses up dopamine which tends to relax a person. The problem is that soon after the dopamine is depleted, the body suddenly recognizes the shortage and immediately gets busy producing more dopamine. It's this up and down chemical reaction that makes working out so addictive. It's relaxing right after the fact, but it leads to tension that can later only be relieved by more exercise.
Competitive exercise produces dopamine, and can keep the level elevated long after the exercise.
Another interesting neurotransmitter is serotonin. Whereas dopamine may be associated with the jock or competitive business man, serotonin might be best demonstrated in a well centered monk. When present, serotonin creates feelings of well being, relaxation, personal security and restful sleep. It helps the brain to be more focussed and less distracted. Emotions like joy, peace and happiness are usually triggered by normal or higher serotonin levels.