Some scientific judges are giving poor scores for the efficacy of cupping, a pain-relief therapy that's been drawing attention at the Olympics because of its use by athletes, including American gold medal swimmer Michael Phelps.

"Cupping is one of those things where there's very little good scientific evidence, very little good research done on it," said Timothy Caulfield, Canada Research Chair in health law and policy at the University of Alberta. "There's very little evidence to support it."

"For me personally I'm very very skeptical about the science of cupping," said Caulfield, author of Is Gwyneth Paltrow Wrong About Everything?: When Celebrity Culture and Science Clash.

Yet athletes like Phelps and  U.S. gymnast Alex Naddour seem to swear by the centuries-old traditional Chinese medicine practice, and have the purplish circle spots on their body caused by the technique to prove it. 

"I wouldn't say he was on it right away," Keenan Robinson, Phelps's longtime strength-and-conditioning coach, told Time. "When he realized it would take five minutes and that this could get him from Tuesday to Thursday [workouts] and from Thursday to Saturday [workouts], he was on board."

The method uses actual cups, glass or plastic, that are placed on the area of the body experiencing pain. The glass cup can be heated while the plastic cup is attached to a pump — both creating a suction force that draws skin up into the cup.

It's about a five- to 10-minute process that, according to cupping advocates, activates a person's Qi, or what traditional Chinese medicine practitioners describe as an individual's life force. 

The technique stimulates blood flow, drawing toxins and old stagnant blood from deep within the body to the surface below the skin layers, according to the website of Dr. Mee Lain Ling, a Richmond B.C.-based practitioner of TCM. (There's also wet cupping, which includes using a needle to make shallow pinpricks into the skin.)

Those circular welts covering the bodies of athletes who use this method are a result of the temporary bruising created by the suction breaking the blood vessels under the skin.

'It's a supernatural idea'

"This idea we have this life force energy running through our bodies and we can use various techniques to balance or adjust or heal that life force energy — it's a supernatural idea, not one that has any scientific foundation," Caulfield said.

NADDOUR VINDICATION Gymnastics

U.S. gymnast Alex Naddour is also a big proponent of cupping. (Jeff Roberson/ Associated Press)

Applying suction to key parts of the body to restore the balance or flow of the blood and other fluids is a theory from centuries before scientists understood how blood flows or how diseases are caused, said Rachel Vreeman, director of research at the Indiana University Center for Global Health.

"There is no strong scientific evidence that cupping provides pain relief," said Vreeman, who has co-authored a number of books debunking health myths.

"Cupping basically causes a hickey, and it will go away."

Some studies seem to have shown that cupping does provide some pain relief. But Vreeman said a 2012 review of 135 studies from 1992 to 2010 found they were not well designed and more rigorous research would be needed to recommend cupping for any of the problems they evaluate. 

Trial results of 'very poor quality'

Edzard Ernst, professor of complementary medicine at the University of Exeter's Peninsula School of Medicine, said some of the most recent trials from China showing positive results are of "very poor quality," not "worth the paper they are printed on" and are likely due to the placebo effect.

And athletes, who are totally concentrated on their body, are ideal placebo responders, he said.

"I think this is the effect they benefit from when they use cupping. I understand why athletes use it. They are not allowed to go anywhere near drugs during the Olympic Games."

But these Olympic athletes, who occupy a big stage, may also be legitimizing cupping for the rest of the population, Caulfield said.

"You have these athletes that are putting everything on the line and they're turning to this and that's sort of a powerful endorsement, which I think is unfortunate."

'Important to keep an open mind'

But Ling said her clients, who include former professional athletes, body builders and just average people, have experienced great success with cupping 

"It's really important to keep an open mind about the different modalities that have been in use, not just for centuries, but millennia, in other cultures around the world."

"If people remain closed before they know anything about it and they're not willing to do the research or not willing to participate in what has already been done, or to explore it for themselves personally then that immediately shuts the door."