AMPSport has a very useful set of commenting features.
You have already read about the Coaches' Notes. The Coaches' Notes is a way for coaches to talk to each other about an athlete, in general.
Users can also talk to each other on the AMPSport site about specific shared items. Anytime you visit a shared item (a link, video, image, page, other file) you have the opportunity to comment on it:
The comment you make will show up in the news feed of other users who are able to see the shared item:
This is so that users can follow the conversations about the shared items that are relevant to them, without having to visit all of the shared items.
This will appear on the Latest News panel (top left) of their AMP Profile page: