do exercises that elevate your heart rate (ie. cardio) burn muscle? i was talking to a friend about doing a 10K run in 2 months and he told me that exercises that raise your heart rate over something around 140 begin to burn muscle as energy. im not a complete noob when it comes to health but i realize that most users of F&N would know a lot more about these things than i would and this is the first time ive heard of burning muscle as energy (that is in terms of working out and not as a survival mechanism against starvation.) i did a cursory search on google and most signs point to no but if anyone would know, it would be F&N users. so what do you guys think? is my friend just misinformed?