The ability to live a happy and well-balanced life. Fitness involves not only physical factors, but it also has intellectual, emotional, social, and spiritual components. These components interact and are interdependent so that if any component deviates from normal it affects the overall fitness and ability of an individual to meet the demands made by his or her way of life. Clearly, fitness is a relative term that depends on an individual's circumstances and aspirations. Fitness is also specific to a particular physical activity: a person fit to run the marathon will not necessarily be fit to do gymnastics (see physical fitness.)