Extreme Exercise Classes

The sun's not even up, but Andrew Vogel is warming up for a workout that most would consider punishment.

"The reason I show up to take this class at 6:00 a.m. is it's really a challenge."

Challenge may be an understatement as the high intensity interval training class is so grueling you have to be invited or approved by the instructor to take the class.

"I just want to make sure you can handle the amount of volume and workload that we do," said Eric Salvador, Fhixtreme Class Instructor.

Salvador is a personal trainer and ex-marine-- he designs the class that combines rounds of kettlebell throws, pull-ups, and an intense set of push-ups.

Sure crossfit has some of these moves but here, there are no modifications allowed and everyone keeps score.

"When you write someone's time on the board and all your peers are watching, like, ya know, there's a sense of accountability. You're like, I'm gonna go a little harder," said Salvador.

Extreme classes are gaining in popularity. There are underground classes and even a girls' only secret class. All designed to take you out of your comfort zone.

"This is certainly exciting to athletes who maybe have done a high intensity interval training class but now maybe want to push their body to the next level," said Dr. Karen Sutton, orthopedic surgeon.

Dr. Sutton is an orthopedic surgeon at Yale University who loves crossfit herself. She has no problem aiming for the extreme if you listen to your body.

"Some of the concerns may be is that you start the competitive nature of it and you lose that self-awareness of when you're exercising. So, your body potentially may be pushed above the limit that it can do."

And if you do? Dr. Sutton says you risk tendon problems, muscle pulls, or low back pain.

Vogel said he is always careful and believes the class has taught him an extreme lesson.

"You can be younger every year that you can have, that you can maintain a level of fitness that definitely bleeds over into other areas of your life."

Exercise experts say you should always look for a class with a high instructor to student ratio.