Answer:
Ok, my first time answering a question!
Explanation:
Normally, your body uses cellular respiration to make ATP.
Cellular respiration needs oxygen to function.
When you exercise or exert yourself, you may begin to run out of oxygen.
Your body then begins fermentation.
Fermentation then makes it so energy can be released from glucose even though oxygen is not available.
Fermentation will also produce ATP, just like cellular respiration.
Hope this helps! :)