As a college athlete turned personal trainer, Jacque Crockford thrives on intense physical activity. So when she left a new body weight workout class one hot day about five years ago, she was unsettled to feel beat up rather accomplished. “I basically had intense swelling and pain in my upper body,” says Crockford, then 28, who’s also an exercise physiologist with the American Council on Exercise.

Soon, she noticed her urine looked more like Coke than lemonade and called an emergency nurse friend, who confirmed her suspicion: She likely had rhabdomyolysis, a rare, serious condition caused by intense physical stress on the body — be it through a traumatic accident like being crushed by a piece of machinery, extreme physical activity like military training or even just a workout you’re not prepared for. The stress causes muscle tissue to break down rapidly and release muscle cell byproducts, including a protein called myoglobin, into the bloodstream.

“The kidneys have to be able to cycle through that [myoglobin] and clean out the blood and unfortunately, that’s a difficult task” when there’s so much to filter, Crockford says. “That can lead to kidney failure, [which] can lead to death.”

[See: Signs You Should Stop Exercising Immediately.]

Obviously, Crockford lived to tell the tale, thanks to her own swift recognition of the condition and her friend’s guidance on how to monitor her health and heal. Rarely, people aren’t so lucky. According to one study, for instance, people who develop rhabdomyolysis and, later, acute renal failure after a severe injury, have a 20 percent mortality rate. “It’s a problem, and it’s very dangerous,” Crockford says.

And while it’s unclear how many people develop or die from the condition after intense physical activity, there are media and case reports showing that it happens — and the consequences can be severe. Just this summer, a 33-year-old Los Angeles man was reportedly hospitalized for seven days with rhabdo after taking his first SoulCycle class. A recent study also documents a 31-year-old woman who was hospitalized with rhabdomyolysis two days after a CrossFit workout. Another study published last year reported a 34-year-old man’s bout with heat stroke and rhabdomyolysis after running a half-marathon. Years ago, the condition was even reported in a 25-year-old woman who collapsed after a four-hour hike through the Grand Canyon.

“Any strenuous exercise can do it,” says Dr. Joshua Tobin, chief of the division of trauma anesthesiology at the Keck School of Medicine of the University of Southern California, who has treated people with rhabdo. “If you’re overdoing it, you’re setting yourself up for the potential risks of this.” But the line between challenging yourself enough to grow and setting yourself up for (kidney) failure isn’t always easy to decipher — especially if you hear the message “harder, faster, stronger” louder than “listen to your body.”

[See: How to Know If You’re Exercising Too Much.]

“A lot of people have decided that doing high-intensity interval training every day is a good thing, and that’s not necessarily the case,” Crockford says. “You have to incorporate rest days, and you have to listen to your body when it’s telling you, ‘I just don’t want to do this today.'”

Here’s what else you can do to reduce your risk of rhabdo — and handle it smartly if it strikes:

1. Know your risk.

To be sure, rhabdomyolysis is very rare: One study, for instance, found that 26,000 cases are reported each year in the U.S., and an unknown fraction of those are caused by physical activity. The condition can also be caused by drugs, toxins, infections, electrolyte and metabolic disorders, genetic disorders, prolonged bed rest and more, one study reports. When it comes to exertional rhabdomyolosis, Crockford says, “the general population of people wouldn’t be able to reach this level of intensity.”

Still, some people, when put under certain conditions, are at greater risk than others. “There’s a perfect storm that can happen,” Crockford says. Namely, when people with a relatively high amount of muscle mass launch into an exercise routine they’re not in shape for. Throw in dehydration (often due to high temperatures) and certain medications like non-steroidal anti-inflammatory drugs, and that storm may erupt, since both strain the kidneys, experts say. People with kidney problems, a history of kidney failure or who have had rhabdo before should also be cautious, Tobin adds.

2. Ease into exercise.

Even if you don’t fall into a higher risk category for rhabdomyolysis, no one is immune to the condition, and the advice for preventing it is good advice for exercisers in general. First, experts emphasize, don’t take your exercise from zero to 100 overnight, whether that means couch to boot camp or half-marathon to ultramarathon. “I have firsthand experience with not progressing appropriately in exercise,” Crockford says. “Regardless of what you’re used to doing or what you did in the past, take your time and do it right, and you’ll save yourself some pain in the long run.”

3. Monitor your hydration.

Whether or not it’s hot outside, staying appropriately hydrated can help prevent the added toll dehydration takes on the kidneys. Stay on top of your hydration by making sure your urine is a light yellow color — darker indicates dehydration and very dark (like the Coke color Crockford saw) indicates rhabdomyolysis since your body is excreting those muscle cell byproducts. Nearly clear urine is worth noticing too, since it could indicate hyponatremia, or the overhydration. “It isn’t as well-known, but it can be just as dangerous as dehydration and can cause death,” Crockford says. Try licking your sweat — seriously — to see if it’s overly salty, which could indicate you’re losing too many electrolytes and need to replenish those with something like an electrolyte-enhanced drink.

[See: 8 Ways to Stay Hydrated This Summer Without Drinking Water.]

4. Know the signs — and get help.

In addition to Coke-colored urine, people with rhabdomyolysis generally experience a more severe level of pain and fatigue in particular muscles after exercise than normal. Significant swelling and nausea can accompany it, too. If you suspect you either have or are on a downward spiral toward rhabdo, seek medical attention right away. While some people like Crockford can heal without going to the hospital (she made sure to rest, rehydrate and monitor her urine’s color and quantity; not urinating at all would be a sign of kidney failure), others need intravenous rehydration with close expert monitoring. In the most severe cases, some people may even need renal replacement therapy, Tobin says. All in all, with quick, expert care, most people can recover completely.

“It’s nothing to be afraid of,” says Crockford, who is still a fan of body weight workouts — when she’s appropriately worked up to them, of course. “Most people don’t have anything to worry about.”

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Rhabdomyolysis: The Deadly Reason You Need to Ease Into Exercise originally appeared on usnews.com