Physical fitness comprises two related concepts: general fitness (a state of health and well-being) and specific fitness (a task-oriented definition based on the ability to perform specific aspects of sports or occupations). Physical fitness is generally achieved through exercise, correct nutrition and enough rest. It is an important part of life.

In previous years, fitness was commonly defined as the capacity to carry out the day’s activities without undue fatigue. However, as automation increased leisure time, changes in lifestyles following the industrial revolution rendered this definition insufficient. These days, physical fitness is considered a measure of the body’s ability to function efficiently and effectively in work and leisure activities, to be healthy, to resist hypokinetic diseases, and to meet emergency situations.

Specific or task-oriented fitness is a person's ability to perform in a specific activity with a reasonable efficiency: for example, sports or military service. Specific training prepares athletes to perform well in their sports.

Examples are:

*400m sprint: in a sprint the athlete must be trained to work anaerobically throughout the race.
*Marathon: in this case the athlete must be trained to work aerobically and their endurance must be built-up to a maximum.
*Many fire fighters and police officers undergo regular fitness testing to determine if they are capable of the physically demanding tasks required of the job.
*Members of the United States Army and Army National Guard must be able to pass the Army *Physical Fitness Test (APFT).