(Newser) – Next time you're pushing for one more rep in the gym, it might be better to just stop. Doctors across the country are arguing the popular CrossFit workout could do more harm than good. The cross-training program urges exercisers to go harder and faster, all while pushing through their limits. But going too far with these strenuous drills could cause a condition called rhabdomyolysis. "Rhabdo," for short, causes muscle cells to literally explode, flooding blood vessels with their contents and, in extreme cases, causing kidney failure. One woman said it was more painful than childbirth. The condition is on the rise as CrossFit grows increasingly popular, with over 6,000 affiliated gyms in the United States.