CrossFit gyms are popping up all over. The company that created the exercise program says 10 of its gyms, or "boxes" as they're called, open each day somewhere around the world.

CrossFit, Inc., was founded in 2000 by former gymnast Greg Glassman, who has brought his libertarian leanings into his booming business. Fans love the timed "workouts of the day" that mix together weightlifting, gymnastics and aerobic exercise.

But the intense workouts have sent people to the hospital with extreme overuse injuries. So what's the attraction?

Jarett Perelmutter, owner of Brick, a CrossFit gym in Los Angeles and New York City, joins Here & Now's Jeremy Hobson.

What's your take on CrossFit? Tell us on Facebook or in the comments.

Interview Highlights: Jarett Perelmutter

What CrossFit is

"It is all things functional, meaning that we jump, run, throw, row, lift, slam, carry, crawl over, jump over, anything that can exert yourself and increase your metabolic rate."

Why CrossFit is growing in popularity

"When you gather people together like that, with such a healthy and positive environment, it's going to be something that's going to be addictive, because the barrier of entry is so low. It doesn't matter if you're 20 or 70, if you're missing a limb, if you have a physical or developmental handicap. Nobody cares, we just want people that want to come in and give it their best."

On the risks of CrossFit workouts

"It's not CrossFit that hurts people, it's bad CrossFit instruction that hurts people ... One thing we that do tend to see, is that many of these injuries that are surfacing were preexisting. So if you come into the right CrossFit facility where you have an educated level of staff who can break down your movement, understand where your range of motion weaknesses are, we can uncover much of that. To say that CrossFit is causing the injuries, I believe, is just an incorrect way of stating that."

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