To get some clarification on the definition, you have to first understand that the definition of fitness is comprised of two separate parts. And including both parts makes the definition more accurate. As a matter of fact, the most accepted definition includes a general or health-related fitness component as well as a specific or performance/skill-related fitness (the ability to perform specific aspects of sports or tasks) component. So a definition falls short when it only uses one part.
Some argue that physical fitness should be measured through the use of some type of criteria (for the health-related components of physical fitness). Health-related or general fitness comprises those components of fitness that exhibit a relationship with health status as a result of regular exercise, proper diet and nutrition, and proper rest for physical recovery within necessary parameters. In other words, being in a quality state of health and well-being.
On the other hand, some say physical fitness should be measured through a population-based norm defined by specific achievement scores on various fitness tests that represent desired health standards (for the performance/skill-related components of fitness). Performance/skill-related or specific fitness is a person’s ability to perform in a specific activity with a reasonable efficiency such as sports
or other physical tasks.
Therefore, a good general definition of physical fitness is “Good health combined with proper physical development. In other words, a body that is easily able to fight sickness along with a proportionally defined physique.”
However, a better definition might be “A set of attributes that are either health related or performance (or skill) related. Health-related fitness comprises those components of fitness that exhibit a relationship with health status. Performance/skill-related fitness involves those components of fitness that enable optimal work or sport performance.”
Now after saying all of that, it needs to be stated that it’s not very useful to try and define physical fitness as one, and only one, all-encompassing definition because of the very nature of the concepts involved in defining physical fitness.
On a final note, most government health agencies and exercise scientists, are in fact in agreement that physical fitness can be divided into the following types (known as the 5 components of fitness): body composition, cardiovascular fitness, flexibility, muscular strength, and muscular endurance. Because each of these components can be assessed, quantified and measured to give a general idea of a person’s physical fitness level.
Know that some sources might discuss agility, balance, coordination, and speed along with the 5 components of fitness to help clarify the picture of establishing someone’s fitness level. In addition, you may also find that some sources include mental and emotional health as an important part of overall fitness.