As per WebGuy:
I've asked three different cadre members to confirm this, and received the same answer each time. If a basic has any type of medical condition, they wear a blue belt. Now, the medical condition can be something very minor. It gives the cadre notice that they need to ask before they begin the different activities to ensure their basics are not restricted from that activity. For example, is someone just pulled a leg muscle and is on 24 hour restricted duty, you don't have them run the Obstacle Course.
Exception: If the person has a double blue (an "X"), they are used as road guards.