1. at 20 seconds into the race, anaerobic glycolysis is responsible for atp in muscle contraction, what would be the primary substrate fueling this system? why? 2. what is a by-product of anaerobic glycolysis? what is something you have heard about this by-product related to exercise and sport? 3. at 38.6 seconds, the aerobic is predominate. why would carbohydrates (glycogen) and not fats be the fuel source for atp synthesis? bonus: (1 point) feedback on watching an event to understand the energy systems rather than just reading about it.