This maybe related to exercises role in positively affecting the immune system.
Look how correcting two seemingly minor mistakes—a space and an apostrophe—makes this sentence understandable:
This may be related to exercise’s role in positively affecting the immune system.
Here’s another instance when a space makes a whole lot of difference: “overtime” is not the same as “over time.”
The game went into overtime. (noun)
I grew to like him over time; when I bought that watch, however, I knew I was in love. (adverb phrase)