Can a person lose significant muscle through exercising by catabolic processes? I always thought that one burned glucose first (from carbs/sugars), then stored glycogen, then fat, THEN muscle (only at the last post-fat stages of non-eating).

ACTUALLY, DEPENDING ON THE LEVEL OF ACTIVITY, YOUR BODY CAN GO INTO MUSCLE CATABOLISM BEFORE FAT STORAGE.... YOUR BODY CAN CONVERT MUSCLE TO GLYCOGEN FOR QUICKLY NEEDED ENERGY, THOUGH IT DOESNT LIKE TO.. THIS IS WHY HARDCORE EXERCISE ON lOW CAL DIETS IS NOT RECOMMENDED
FOR LOW GRADE ACTIVITY (SLEEPING, MAKING DINNER, GOING TO THE GROCERY STORE) YOUR BODY PREFERS TO BURN FAT, ASSUMING THERE ISNT READILY AVILABLE GLYCOGEN