Games audiences could have been forgiven for consulting Dr Google en masse after images emerged of 19-time Olympic gold medallist Michael Phelps covered in large red spots.

Fox Sports US noted that Phelps had about a half-dozen red circles on his upper body, like the world's biggest, most concentric chicken pox or a Gatorade bottle had given him a hickey. What's the deal?"

The answer was far less troubling (or contagious).

"It's called cupping therapy," Fox Sports US continued.

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"A Chinese (or Egyptian, depending on who you believe) medicinal practice that dates back thousands of years. It works pretty much in that Gatorade hickey way. Back then, cups were made of glass and, inside them, a flammable material was set aflame."

They concluded: "For athletes, the idea is that the practice helps in recovery, something that's important for both post-practice purposes and in an eight-day stretch when you might swim a dozen races."

Sonny Bill Williams and the bizarre 'cupping' treatment

The idea is not new and has been used by Kiwi athletes before, most notably Sonny Bill Williams.

Williams shared a photo of him undergoing cupping with the caption "Detox time" with his 500,000 social media followers last November following the Rugby World Cup.

"It's not painful, generally. It probably looks scarier than it is," said Professor Marc Cohen, a holistic medicine expert from RMIT University's School of Health Sciences told news.com.au.

Thanks @arschmitty for my cupping today!!! #mpswim #mp 📷 @chasekalisz

A post shared by Michael Phelps (@m_phelps00) on

"It's supposed to mobilise blood flow and promote a release of stagnant blood, so blood that is not circulating in the body. I know they use it to help with bruising in martial arts."

Professor Cohen said the practice has been around for thousands of years and was used in many ancient medicinal therapies from China, the Middle East and Europe.

There is limited scientific evidence available on cupping therapies.

A 2008 study of 70 patients with chronic headaches or migraines, published in The American Journal of Chinese Medicine, found that headache severity decreased by 66 per cent following wet-cupping treatment. "We conclude that wet-cupping leads to clinical, relevant benefits for primary care patients with headaches," the study said.

According to a 2011 study published in the Focus on Alternative and Complementary Therapies journal, two out of three reviews into the effectiveness of wet and dry cupping found "some evidence" that cupping worked in treating pain.

What is hijama cupping?
• Cupping is said to improve blood flow to encourage healing, targeting ailments including colds, joint pain, acne, migraines and even facial paralysis.

• Dry-cupping involves holding a cup to the skin and using either heat or suction to reduce pressure.

• Hijama cupping or wet-cupping involves making incisions 1.5mL deep and 1.5mL wide to try to remove "superficial bloods".

• The blood 'filled with toxic chemicals' is said to flow into the cup.

• The benefits of cupping have been detailed in Islamic scriptures.

The prophet Muhammad is quoted as saying: "How good is the cupper, removes blood, lightens the back and sharpens the eyesight" and "Indeed the best of remedies you have is hijama, and if there was something excellent to be used as a remedy then it is hijama."