I am going to throw two very different definitions of fitness on the table. Greg Glassman the creator of CrossFit, an increasingly popular fitness protocol (often called the sport of fitness), has taken a very good stab at defining fitness. Here is his definition:
"Fitness in 100 Words:
• Eat meat and vegetables, nuts and seeds, some fruit, little starch and no sugar. Keep intake to levels that will support exercise but not bodyfat.
• Practice the major lifts: deadlift, squat, presses, C&J, and snatch. Similarly, master the basics of gymnastics: pull-ups, dips, rope climb, push-ups, sit-up, press, handstand, pirouettes, splits, flips, and holds. Bike, run, swim, and row fast and hard.
• Five or six days per week mix these elements in as many patterns as creativity will allow. Routine is the enemy. Keep workouts short and intense.
• Regularly learn to play new sports."
Although I really like many of the elements of this definition of fitness I find it a bit dogmatic. There doesn’t seem to be a whole lot of spectrum or freedom of choice within Glassman’s definition.
In my humble opinion the definition of fitness is not a one-size-fits-all concept. The definition should be malleable, so that it has the potential to be sculpted to fit one’s own unique definition that is only applicable to that person.
Dan John defines fitness as “being better at what you want to do.” Although this definition is somewhat vague, I think that it is a step in the right direction in contrast to the inflexible CrossFit description.
Here is my own attempt at defining fitness, I call it “Fitness in 15 Words;”
“Actively seek progress as an athlete by setting reasonable athletic goals and continually achieving them.”
This definition is applicable to anyone and everyone. You can set any goal you like as long as it is quantifiable and reasonable. I would wager that 70-90% of the people who are concerned with their physical fitness simply want to look better, which is fine. So set a goal, for example to be able to see your abs, getting below 10% bodyfat, or having a certain sized waist or butt or whatever. Maybe your goals are related to health and longevity, for example reducing your A1Cs (a test that measures a form of hemoglobin used primarily to identify the average plasma glucose concentration over prolonged periods of time; people with high (above 6%) A1Cs may have diabetes, people with good A1Cs (in the 5% and below) live for a very long time on average). This link delineates the importance of the A1C test: http://www.longevity-and-antiaging-secrets.com/A1C-blood-test.html.
One of my goals right now obviously is to dunk a basketball. Maybe your goal is to impress people with your athleticism, in which case you probably want to be proficient in gymnastics movements like handstands, backflips, planches, etc. The goals don’t really matter, what matters is that they are at least transiently related to athletic endeavors and that they are achievable (within reason). Maybe your first goal is a pull-up, then your next goal is a muscle-up, then your next goal is a backward roll to support on rings, and so on.
Once you achieve your goal there is always another more difficult goal to achieve, consequently the search for fitness is never truly complete. In my opinion one is fit when one feels fit. Fitness is all about perception.