Imagine that you are exercising as hard as you can and you begin to breath extra hard and you just don't know if you can continue. At this point, will you burn more fat or sugar in your muscle cells
ALSO ON HUFFPOST:Unexpected Side Benefits Of ExerciseSuggest a correctionSarah Klein Senior Editor, Health & Fitness; Certified Personal TrainerMORE:Huffmag Your Body On Exercise Best Of Huffpost Exercise Physiology Body On ExerciseCONVERSATIONS
