The P90X workout is one of the biggest fitness trends in the past several years, with enthusiastic endorsements across the cultural spectrum, including everyone from singer Pink to 2012 Republican vice presidential nominee Paul Ryan.

But businessman Matt Lombardi says just one day of the program’s strenuous routine sent him into the emergency room with near kidney failure.

“I simply wanted to get back in shape. I could have killed myself in the process,” Lombardi writes on his site, College Spun.

Lombardi says he has “always been an athlete” and that he didn’t wander recklessly into the program. Instead, he says he wanted to try P90X to help lose the 20 pounds he had gained while developing College Spun.

After completing only half of the first day of workouts, Lombardi said he woke up the next morning feeling sore and ill.

“If you’ve done P90X, then you know that the first day (chest & back) is really, really difficult,” he writes. “You’re asked to do push-ups, then pull-ups, then push-ups, then pull-ups. I lost count of my how many of each I did — but it was a lot. Eventually, my muscles just shut down.”

Despite the pain, he decided to try day two of the program. Instead, he found himself back in bed. On the third day, he describes using the bathroom and being shocked when his urine “looked like Coca-Cola.”

After a quick Web search, Lombardi guessed he was experiencing rhabdomyolysis. The National Institutes of Health describes the condition as “the breakdown of muscle fibers that leads to the release of muscle fiber contents (myoglobin) into the bloodstream. Myoglobin is harmful to the kidney and often causes kidney damage.”

The condition is commonly brought on by excessive physical activity and results when excessive toxins are released into the bloodstream.

So, why did Lombardi end up in the hospital when thousands of other individuals, many without a background in athletic activity, have a positive experience with P90X? Several experts warn that jumping into P90X, or any intense workout routine, without taking proper precautions poses a wide array of risks.

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Of course, like any other trendy exercise program, P90X is not without its critics. In a YouTube video, Dr. Jarod Carter, a doctor of physical therapy, jokes that the program has been great for his business, by increasing the number of patients who come to him with lower-back pain resulting from P90X.

“I see a lot of people trying to do, or being asked to do, abdominal exercises that their abs are simply not strong enough to actually do,” he says in the video.

“I’ll be honest — P90X has a number of ‘warnings’ about what strenuous exercise can do to your body,” Lombardi wrote. “But if I’d specifically known about rhabdomyolysis, I don’t think I’d have ever even taken the plunge.”

Lombardi then checked himself into an emergency room, where he says the levels of toxins in his bloodstream were literally off the charts.

“My blood test came back with a CPK (creatine phosphokinase) level of over 16,800 (the max they can test for),” he wrote. “Normal CPK levels, I was told, usually run between 10-200 micrograms per liter. These levels are a huge indicator of severe rhabdomylolysis.”

Doctors hooked him up to an IV, Lombardi wrote, and he spent the next several days under observation while doctors waited for the toxicity levels in his bloodstream to return to normal.

Going forward, he was told to approach future exercise routines with caution.

“My two biggest takeaways from the entire ordeal? You can’t put your muscles through a strenuous workout without leading up to it, and you need to recognize when you’re body is telling you that there is something wrong,” Lombardi writes. “The first could have killed me, while the second may have saved me.”