Once, I remember reading that glycogen and glucose can be used anaerobically by muscles, but fat cannot. So when you’re doing some kind of endurance excercise or marathon, you hit the wall once your muscles have run out of glycogen. Since fat can’t be metabolized anaerobically, this means that you need to breathe in even more oxygen just to put out the same amount of energy. Basically, all this makes you feel extra exhausted and out of breath.
Is that true?
Fat can be burned anaerobically but it’s a slower release of energy than glycogen.
You slow down simply because you can’t produce energy fast enough for a faster pace.
Going anaerobic means you’ve already exceeded your body’s capacity to absorb oxygen. Running that fast also means you don’t have much more capacity to breathe in more oxygen, you’re already at or very near your limit on respiration rate.
Sled dogs appear to have some not completely understood mechanism to start burning fat directly in muscles instead of glycogen.
interesting, but it doesn’t say that they do this anaerobically. Just imagine the extreme endurance you would have if you could anaerobically burn fat directly.
anaerobic glycolysis (the metabolic pathway from glucose to pyruvate) yields 2 molecules of ATP (the energy unit used by cells) per molecule of glucose. Under anaerobic conditions, the pyruvate is converted to lactate to recover the NAD+ needed for glycolysis to occur.
Under aerobic conditions, the two pyruvate molecules are converted to two Acetyl-CoA, which enter the TCA cycle and yield another 30-38 molecules of ATP.
The breakdown of fatty acids yields several Acetyl-CoA (depending on chain length), (actually requiring ATP), which also have to be metabolized in the TCA cycle. Anaerobic metabolism is very inefficient compared to aerobic metabolism.