That cardio burns muscle is one of the most commons reasons you hear about why you shouldn't do cardio if you want to build muscle mass. But is it true, does cardio burn muscle?
Cardio Does Not Burn Muscle
No, your muscles have nothing to fear from cardio. No matter if you go running or biking or whatever else you enjoy doing.
Because the protein used during cardio comes from a different source than your muscles. It would be much too complicated for your body to transform the protein in your muscles into something it can use for energy: