Cupping is one of the oldest methods of traditional Chinese medicine, dating back to the early fourth century, when the noted herbalist Ge Hong wrote about a form of cupping in A Handbook of Prescriptions.
This is another line of reasoning taught about the value of this practice. It is promoted to massage therapists, some of whom have their own unique spin to this belief system (not that I am judging it however). But, we do have a therapeutic route established for the treatment, akin to that taught to an LMT.
Mets Latch On to Cupping Therapy, and Have the Marks to Prove It
The Mets (and our own Oakland A's) are using the Chinese therapy of cupping. "Nick Paparesta, the trainer for the Oakland Athletics, said in an interview that virtually the entire A's roster has undergone cupping therapy at some point this season. Paparesta called it a 'twofold solution' because it can provide both immediate and long-term relief of lower back or oblique tightness, and can be done post-surgery to help reduce scarring."