Professional athletes are getting injections of stem cells to speed up recovery from injury. Critics call it a high-tech placebo.

NFL quarterback Peyton Manning reportedly had a stem cell treatment to his neck in 2011.

Elite athletes do whatever it takes to win. Lately, thats meant getting an injection of their own stem cells.

The treatments, developed over the last eight years, typically involve extracting a small amount of a players fat or bone marrow and then injecting it into an injured joint or a strained tendon to encourage tissue regeneration. Bone marrow contains stem cells capable of generating new blood cells, cartilage, and bone.

Although the treatments have become a multimillion-dollar industry, some doctors say theres only thin medical evidence they actually speed healing. In a report issued last week, public policy researchers at Rice University criticized the National Football Leagues role in promoting unproven treatments to the public. Some players, including Peyton Manning of the Denver Broncos and Sidney Rice, whos now retired but won a Super Bowl with the Seattle Seahawks last year, have reportedly gone overseas for stem cell treatments and others have acted as spokespeople for U.S. clinics offering them.

The Rice researchers, Kirstin Matthews and Maude Cuchiara, say the NFL should create an independent panel and fund research on whether stem cell treatments actually work, similar to what it did after facing questions around concussions and brain injury. I think they should be more proactive. They should get ahead of this one, says Matthews.

Sports Illustrated reports that hundreds of football players have gotten stem cell treatments, with many travelling abroad for types of therapy not offered in the United States.But its not only football players trying them. The tennis player Rafael Nadal is reportedly undergoing stem cell treatments for back pain, and the injections are also being sought out by soccer players and high school athletes.

The NFL didnt respond to questions from MIT Technology Review. Doctors offering the treatments say theyre promising and should be given a chance. Others say theres not enough data. Any of these injections have a placebo effect, says Freddie Fu, an orthopedic surgeon who is chairman of sports medicine at the University of Pittsburgh Medical Center and top doctor for the schools sports teams. We dont know what we are putting in. We dont really know what exactly what it does, biologically.

Orthopedic surgeons hope one day to use stem cells to regenerate cartilage and other lost tissue. But wishful thinking, and profits, have gotten ahead of the facts, says Fu. Theres a lot of marketing in orthopedics right now. I would say 15 to 20 percent of treatments are not effective, he says.

Unlike a drug, which gets tested for years and is then weighed by experts and the U.S. Food and Drug Administration before hitting the market, the bone marrow treatments offered in the U.S. arent regulated.

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The NFL Has a Problem with Stem Cell Treatments