This Popular Ab Exercise Is Probably Doing You More Harm Than Good

What does having a strong "core" actually mean, anyway? The problem with this kind of ambiguous term is that it's prone to oversimplification. We might assume that toned abs are the sign of a strong midsection, for example—or worse, that we can build one with one type of exercise. (Crunches: They just refuse to die, don't they?)

In reality, it's a little more complicated than that. Our "core" is comprised of an entire network of muscles, which, in turn, impacts all kinds of bodily functions—down to the way we breathe. This also means that a one-exercise-fits-all approach isn't going to cut it. (It can even lead to injury, if you're not careful.)

But if you work those muscles correctly, the benefits abound: Better posture, endurance, and even digestion, to name a few. With this all in mind, we turned to trainer, yoga instructor, and THE/THIRTY contributor Claire Fountain for a crash course in core-building. Class is in session below.