I think my favorite topic in this class was learning about the immune system and how it can be impacted by exercise. I always thought that working out in the cold would make you sick, and that working out more (higher intensity) meant better health. Now that we understand how the immune system works and how the health benefits only arise after moderate exercise, I feel like I understand why people who over-exert themselves can tend to get sick. I like how the immune system chapter was easy to relate the different cellular components to the effects we feel on a macroscopic level. Being able to relate the open window theory to Endure was also helpful because I feel like we were able to see how the immune system can be compromised in different environments and during endurance training.