What is the black patch on misty may's shoulder during the Olympics?

It's "Elastic Therapeutic Taping" used in rehabilitation and sports medicine. It was not developed by Dr. Kenzo Kase more than 25 years ago in Japan, but by Komp who had the patent in 1970. It's believed to improve circulation in her joints. It's being applied by FIVB (international volleyball federation) physiotherapist Periklis Charpantidis. Link to the inventors web site provided below.