The document discusses Usain Bolt running 100m in 9.58 seconds and asks what is happening with his respiration. It then asks if anything is different from last week and why. The document introduces the anaerobic system and its role in energy production compared to the aerobic system. It outlines understanding levels from knowing the anaerobic system and its components (C grade), to understanding how it differs from aerobic during energy production (B grade), to being able to see links and differences between the two respiratory systems (A* grade).