Exertional rhabdomyolysisbut is a rare but life-threatening condition, sometimes caused by extreme exercise, in which overworked muscles begin to die and leak their contents into the bloodstream, straining the kidneys and causing severe pain. A study published in the American Journal of Medicine found that the majority of people seeking emergency medical help for this condition after a spin class did so after their very first class, indicating the issue is inexperienced people overexerting themselves. "Spin class is a great exercise," the study's co-author Alan Coffino, M.D., Ph.D., told The New York Times. "But it's not an activity where you start off at full speed. And it's important for the public to realize this and for trainers to realize this."

While the condition is extremely rare, it's essential you resist pushing yourself beyond what is comfortable for you when beginning an exercise regimen like spinning. It's okay to be a beginner. Sometimes, the instructors in spin classes are almost like drill sergeants, barking encouragement and urging you to push, push, push, but you shouldn't allow this to push you past your own healthy boundaries. Dr. Maureen Brogan of New York Medical College told Time, "I mean, Spinning, you burn 600 calories in an hour, and you lose up to a liter an hour of sweat," she commented to Time. "Six hundred calories is like running six miles. So if you're not conditioned, you wouldn't just run six miles."