Physical fitness is to the human body what fine-tuning is to an engine
It is not a race, it's a pursuit. In its most general meaning, physical fitness is a general state of good physical health. It is a foundation for a long and successful life.
Physical fitness is usually measured by periodic tests measuring strength, endurance, agility, coordination, and flexibility. Physical fitness is the capacity of the heart, blood vessels, lungs, and muscles to function at optimum efficiency.
It has two meanings -- General fitness (a state of health and well-being) and specific fitness (the ability to perform specific aspects of sports or occupations). Physical Fitness is important, even on bed rest.