Moderate exercise is great for improving immune function, but intense exercise, especially lasting longer than 90-minutes, can impair immunity. This can lead to increased risk of infection and other issues that most bodybuilders would like to avoid. Check our other posts on exercise and immunity to learn how to avoid this!
Source: Nieman, D. C. (2003). Current perspective on exercise immunology. Current Sports Medicine Reports, 2(5), 239-242.