In the past physical fitness used to just be focused entirely on athletic performance but today it includes modern health related aspects as well. This evolution of the definition of fitness can be attributed to the complexity of the term and the fact there were so many definitions of the term in the past with everyone defining it according to their own individual needs and requirements.
Even the government health organization and agencies seem to be defining fitness differently despite agreeing on various aspects. To understand the concept of fitness we need to divide it into two parts. Physical fitness comprises of general health related fitness component as well as a specific performance related fitness component. Including these two parts makes the concept of fitness more accurate and without it the definition will certainly fall short.
Health related components of fitness includes all those components that exhibit a relationship between our health status whereas performance and skill related fitness includes such components that enable us to optimize all our work and sports related performance.So now we can define physical fitness as the combination of good health and proper physical development. Such a body not only has a well-defined physique but is also able to fight various diseases.
It is for this reason that government health institutes and agencies have divided physical fitness into five components that are body composition, muscular strength, flexibility, muscular endurance and cardiovascular fitness. Every single one of these components can not only be assessed but can also be quantified and measured and hence give us a general idea of our level of physical fitness.