CrossFit may be the biggest fitness craze of the century. In just 15 years, more than 12,000 CrossFit gyms, called “boxes,” have sprung up all over the world. At the same time, these high-intensity workouts, which combine Olympic weightlifting, powerlifting and gymnastics, have gotten a reputation for being dangerous.

Whenever anything gets that big that quickly, it’s going to have critics, says Michael Esco, PhD, assistant professor of kinesiology at the University of Alabama. “I’m all for people exercising and moving their bodies to be healthy. If it weren’t for CrossFit, some would still be sitting on the couch.”

CrossFit cautions

If you're interested in jumping on the CrossFit bandwagon, here's what to know before you get ready to work up a sweat.

It’s super intense. Every CrossFit workout is designed to be fast-paced and to push exercisers to their limits. This might be fine for someone who’s already fit. But working out too vigorously may be dangerous for bodies that aren’t in condition. “It can be as risky as other high-intensity training, such as sprinting or football, if you’re not accustomed to it,” says Esco.

It doesn’t follow traditional progressions. Exercise research has found it’s best and safest to start slowly and increase intensity as strength, agility, flexibility and range of motion improve. CrossFit’s workouts don’t progress this way. For example, you may find yourself doing advanced moves like box jumps — a plyometric exercise in which you jump from a standing position onto a platform, landing on both feet — before you’ve built up the strength and stability to do them safely.

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It’s competitive. CrossFit encourages two kinds of competition — against yourself to lift heavier weights or do more reps, and against other exercisers. On one hand, a little competition is healthy and motivational, Esco says. But sometimes trying to keep up with someone who’s in better shape than you are can cause you to push yourself past your limit. “When a person does more than he can handle and works beyond his capability, he risks getting hurt.”

It can be under-supervised. Very few studies have looked at the risks of CrossFit training. In one, however, a survey of about 400 CrossFit participants, the injury rate was about 20 percent. The survey also found that when exercisers were supervised by qualified trainers, the risk of injury was much lower.

CrossFit has gone viral. Anyone can go to CrossFit.com and follow a Workout of the Day (WOD). Convenient, sure, but potentially dangerous. “For some people, doing this without supervision can be a problem,” says Esco. Even at CrossFit boxes, the quality of coaching can vary (true for any kind of workout). While some coaches are very good and well qualified, others may not have the knowledge or ability to keep vigilant watch over a group of people lifting heavy weights or doing other vigorous exercises all at once.

How to do CrossFit safely

Despite the potential risks, CrossFit can be a fun, dynamic and highly motivational way to get into shape if you follow some smart safety guidelines (a good idea before embarking on any new workout program).

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Be honest with yourself. If you’re generally sedentary or haven’t been exercising regularly, it may not be wise to jump into CrossFit right off the bat (or off the couch). “Start with traditional exercise to build a base level of fitness,” says Esco. Besides, CrossFit fees can be as much as triple those of other gyms, so it may make financial sense to start out spending money on basic classes or personal training before you sink a fortune into CrossFit.

Don’t jump into the first box you see. The philosophy and environment of CrossFit facilities can vary. Before you commit to one, observe a few sessions or ask for a trial week. Chat with the trainers and other participants and assess the general vibe. Ask the coach about her credentials and those of the staff.

Get properly introduced. Most boxes offer a multi-week course for beginners that teaches the basic moves that make up a WOD. Even if you think you’re already fit — and especially if you aren’t — take advantage of this. Not only will you learn the skills, you’ll develop a rapport with the instructor and feel more comfortable asking for questions or guidance during a later workout.

Mind your form. Ask coaches to spot you, keep an eye on yourself in the mirror if available and learn what the positions should feel like before you add any weight. If you notice you’re getting tired and your form is beginning to suffer, cut the set short, rather than risk injury from a false move caused by fatigue.

Listen to your body. If something says “stop” or “slow down” or “ouch!” that’s a sure sign to take a break. “This goes without saying in any sort of training program, but especially in one that promotes competitive behaviors,” Esco says. If you develop a problem that persists, see a doctor or physical therapist before it gets worse.

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Amy Roberts is a certified personal trainer. She writes about fitness, health and a variety of other topics for many well-known publications.