The recently completed World Athletics Championships in Tokyo came and went with no shortage of surprises and high drama. But for some fans, the real mystery wasn’t on the track — it was the strange-looking patches on the faces and bodies of Japan’s distance runners.

“Product link please,” one social media user wrote. Plenty of others had their own comments and questions: “I thought they were nicotine patches,” “I thought he was covering up his hickeys,” “Looks cool,” “Diabetic?” “Cupping marks?” “Science or scam?” “Is that legal?”

The beige-colored adhesive discs, which contain microscopic particles of titanium or ferrite permanent magnets, are quite popular in Japan. They are marketed as a way to improve circulation, alleviate stiffness and help active people breathe easier by stimulating blood flow.