Being thin and being in shape are not the same thing, as evidenced by our slender friends who never get off the couch, and conversely, by every single overweight athlete.

Although our weights and where we fall on the body mass index — a measurement of our total body fat based on our height and weight — can give us clues about our health, BMI doesn’t tell the whole story. Plenty of athletes, including Olympians, have had BMIs in a range that would qualify them as obese, for example. You can play around with the BMI calculator on the U.S. National Heart, Lung and Blood Institute to get a good picture of how limited it is as a measurement.

Read: What Is a Calorie and Why Do I Care?

So apart from how much we can lift or how fast we can run a mile, how do we measure physical fitness?


People who are out of shape are more prone to getting hurt. According to an article on the National Institutes of Health, studies have shown that increasing your fitness level also lowers your risk of injury. That is because those who are more fit are not exerting themselves as much — they are performing a task “at a lower percentage of their maximal capability,” so they can do it for longer, are less tired afterward and their bodies recover faster. Being less fatigued during exertion is key because “fatigue alters movement patterns, putting stress on parts of the body unaccustomed to it, possibly increasing the likelihood of injury.”


It’s not the same as flexibility, New York City-based physical therapist and trainer Joe Vega told Men’s Fitness. When people have good mobility, they can “perform functional movement patterns with no restrictions in the range of motion (ROM) of those movements.” A simply flexible person, however, may not have the strength and balance to do the same. “Flexibility is a component of mobility, but extreme flexibility usually isn't necessary to perform functional movements.” Having mobility in your neck, back, hips and calves is particularly important.


There are some times it’s normal to be out of breath and other times when it’s not. If you get a little winded climbing up some stairs, don’t panic — notes that walking up the stairs is a difficult movement, requiring many different muscles and coming on suddenly without a warmup. “Anybody's going to feel a little short of breath going up stairs … even if you're in really great shape.”

But if you are gasping for breath out of nowhere, that could be cause for concern.

See also:

How Much Weight Can I Safely Lose?

10 Best Foods to Build Muscle

How Fast Can You Reshape Your Body?