At Matter, physical therapy professor Eric Robertson writes about a very rare condition called rhabdomyolysis — it’s what happens when chronically overworked muscle cells rupture and overload your kidneys with massive amounts of protein. The results are painful, reasonably disgusting, and potentially deadly. Rhabdomyolysis used to be something you only had to worry about if you were, say, part of an elite military squad or a professional athlete. But as more average folks have gotten into elite physical training regimens through programs like CrossFit, the profile of people damaged by rhabdomyolysis is changing. Training like a bad-ass can bring along some of the physical risks of being a bad-ass.