It’s not just winning his 21st gold medal that has made Michael Phelps the talk of the sporting world these days; the real buzz is about those mysterious round splotches across his shoulders.

So what are they?

These dark purple circles that are dotting the swimmer’s back and shoulders are the after-effect of cupping – an ancient Chinese treatment that uses a small cup to suction blood flow into tight muscles and help relieve pain.

As we reported back in 2013 when stars such as Gwyneth Paltrow and Jennifer Aniston were indulging in the practice, cupping is a form of acupuncture dating back to about 3,000 B.C. by some estimations and is said to mobilize blood and “energy” around the body.

Cupping therapy involves attaching a circular cup to the treatment area using suction created either from heating the cup or by using a handheld pump. The suction then pulls the skin into the cup and bursts blood vessels which cause the purple marks on the skin.

According to Ezard Ernst and Simon Singh in their book, Trick or Treatment: “Cupping is an ancient treatment that has been practiced in places such as China, Vietnam, the Balkans, Russia, Mexico and Iran. Essentially, the air in a glass cup is heated over a flame and the cup is then swiftly placed on the skin. As the air in the cup cools down, a vacuum develops which creates suction. This is visible as the skin and its underlying soft tissue are partly sucked into the cup. Sometimes the skin is lacerated beforehand, and the suction then draws blood from the cutaneous micro-circulation. This form of cupping was popular in connection with bloodletting in Europe.”

It’s used today to treat a variety of conditions from musculoskeletal problems to asthma and eczema. Some practitioners use it to treat infertility, influenza, and anemia.

The treatments last about 20 minutes and repeat sessions are usually required. Because it is considered an alternative medical practice, it is employed mostly by naturopaths, acupuncturists and chiropractors.

“If someone is under stress, or they’ve suffered a physical trauma like a pulled shoulder, the energy in their body can become stagnated,” explained Ian Stones, an acupuncturist and member of the British Acupuncture Council, to the Daily Mail.

“Cupping enables the blood and energy to move again and travel to the area to begin the healing process. It can also have good results if someone is coming down with a cold. The suction can help to stop the cold penetrating further into the system.”

Or so they say.

In reality, there is not a lot of science to back up these claims – but they’re working on it!

For example, Live Science is reporting on a 2015 study conducted by researchers in Germany who tested whether cupping therapy worked better than a sham treatment for patients with fibromyalgia.

“Both the real treatment and the sham treatment used the same type of cups, but with the sham treatment, the cups had a hole at the top so that they couldn’t create the proper suction,” Live Science reports. “Patients in the study were told they would receive either traditional cupping or ‘soft cupping,’ but they were not told that the so-called soft cupping was a sham treatment.”

While most patients correctly guessed whether they’d had the traditional or soft cupping, patients in both groups experienced the same reductions in pain, which suggests “the effects of cupping therapy might be confounded” by effects that are not specific to the treatment itself, the researchers said.

In other words, there is no definitive proof that cupping actually works, although most patients report at least temporary relief from stiffness and pain.

There are no known harmful effects of the procedure other than patients who reported a tingling sensation, strain or pain in the treated area which tended to disappear within four hours.

Marks on the skin can last longer, however, and take anywhere from three days to several weeks to heal.

Christian should be aware that cupping is based in traditional Chinese medicine and is used as one of several ways to stimulate acupuncture points; therefore, it has the same underlying philosophy as acupuncture which is based on the belief that a universal life force known as chi runs through the body through 14 channels known as meridians. Belief in this universal life force is pantheistic and is thus incompatible with Christianity.