It has been reported in a research by Roy Baumeister and Julie Exline that self-control temporarily weakens after exertion, replenishes with rest, and becomes stronger with exercise.
Self-control is an ability to subdue impulses or to regulations one's emotions, thoughts, and actions in order to fulfill specific (longer-term) goals, especially when faced with temptations and impulses. This enables a person to plan, evaluate alternative actions instead of getting carried away by impulses, and prevents him/her from behaving in a way that he/she might regret later on. Willpower is the ability to exert self-control.