It's a strange, vague goal that many of us strive for: getting "in shape."

But what does that actually mean? And how do you get there?

It may be the most popular phrase in the world of exercise, but it's hard to pin down a clear definition, or know how to reach that ideal in practice.

We spoke recently to Shawn Arent, an exercise scientist at Rutgers University, and asked him about this. He was pretty clear: The answer is different for everyone.

But that doesn't mean we don't have a number of common markers for people who consider themselves "in shape."

Here's what he told us:

"There is no one definition. It can be everything from having low body fat to having good cardiovascular endurance to having muscular strength — to be pain free, to be stress free, all these things ... and I really think it depends on what the person’s goals are.

"It depends on what you’re trying to do. If you’re trying to run a marathon, your version of in shape might be something very different than someone competing in a body building contest or someone that plays flag football on the weekend.

"Generally the way we define it is that your cardiovascular endurance — your cardiorespiratory endurance — is good enough that you don’t easily get winded. So your VO2 max is above average, in terms of oxygen consumption.

"[Being in shape can also mean] having a good level of body fat — I don’t want to say low — because obviously you don’t want to go too low with body fat (there’s other problems there), but a healthy [level of] body fat is probably the best way to look at it. Where you’re considered lean, most people consider that “in shape.” So like I said it really depends on what your goals are ...

"... It just depends on what you want your shape to be."

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