A rare side effect of high-intensity workouts is becoming more common

With high-intensity workouts like spinning on the rise, a rare condition is becoming more common among people seeking out new ways to exercise.

Rhabdomyolysis -- or rhabdo -- occurs when overworked muscles begin to die and leak their contents into the bloodstream, which strains the kidneys and causes severe pain.

A report in The American Journal of Medicine highlighted more than 46 cases where people developed the condition after taking a spin class, where 42 of those people took the class only once.

In the past, rhabdo has been common among soldiers, firefighters and others who have physically demanding professions.

But just because you are in shape doesn't mean rhabdo can't affect you. In fact, rhabdo usually affects people who are trying something new, not people who are unfit.

Physiologist Joe Cannon said he's noticed people who tell him they've gotten rhabdo have usually given up personal power in the gym and followed their instructors so they wouldn't appear weak.

The authors of the report said those numbers shouldn't scare you away from taking a spinning, but should serve as a warning to be more cautious before starting a new exercise at full speed.