What do the markings on the back of Olympic divers mean?
They are half right it's a medical adhesive bandage with medicine on it which soaks into the skin and relaxes and heals muscle pain or injuries
If this is what I think you're talking about, it's tape because they might of pulled or hurt a muscle so they put tape over it to keep it in place or so it doesn't hurt as much.
What you see on most of these athletes aren't markings; its tape, kinesio or physio tape. The tape is made of plastic resin and is meant to help stabilize loose joints and relieve strain on soft tissue that may be damaged. See www.wrex.com/story/19231678/kineseo-tape-keeps-olympic-muscles-at-the-top-of-their-game for details.