Every week, the Nuance will go beyond the basics, offering a deep and researched look at the latest science and expert insights on a buzzed-about health topic. This week, we’re looking into claims that fascial therapy can heal everything from sports injuries to cellulite.

Crack open an anatomy textbook and you’ll see that most of the illustrations portray the human body as a neatly defined network of muscles, bones, and organs. Often left out: the fibrous, collagen-dense layers of white fascia that hold everything in place.

The fascia is the covering tissue around any muscle,” says James Gladstone, MD, an associate professor of orthopedic surgery and co-chief of sports medicine at Mount Sinai Hospital.

Gladstone explains that fascia is more or less ubiquitous inside our bodies and has mild elastic properties that allow it to offer snug support even when our muscles swell in response to exercise or injury. The fascia also helps secure organs, bones, and other connective tissues. If the human body were a frittata, the fascia would be the egg.

But fascia is not mere insulation or “packing stuff,” as it’s sometimes described. Along with reducing friction between muscles, the fascia helps transmit mechanical force generated by muscles. Its tautness and pliability play a part in our ability to jump, run, throw, and perform other dynamic movements. The fascia is also not uniform; it comes in different layers and types that perform different functions. For example, research has found that the “deep” fascia layers in the thigh contain specialized cells that aid tissue maintenance and regeneration.

The fascia has long been the focus of medical therapies, both alternative and conventional. A decades-old, trademarked form of deep-tissue manipulation known as Rolfing or structural integration purports to shift or realign the fascia in ways that promote mobility, pain reduction, balance, breathing, energy, and mental fitness.

There’s also a big body of literature on “myofascial release” — a somewhat protean term that refers to kneading or loosening the fascia to improve its pliability. There are a lot of ways to perform myofascial release, from stretching and massage to foam rolling to branded devices like the FasciaBlaster, which, its maker claims, can reduce cellulite by allowing the fascia to “lay flat and smooth” beneath the skin.

While those cellulite claims are unsupported by research, there are studies linking fascia-targeting therapies to real health benefits — from reduction of pain, inflammation, and stress to improved mobility. In fact, Gladstone says he often refers patients for fascia treatment when they’re experiencing muscle pain or soreness in the absence of muscle injuries. “I’ll write a prescription for tissue mobilization or fascia release,” which many physical therapists perform, he says.

But other experts take issue with the claims — including the notion that patients need weeks or months of treatment to stretch or loosen the fascia.

“I think way too much is being made about the importance of the fascia and the various — and expensive — ways to treat it,” says Robert Sallis, MD, a clinical professor of family medicine at the University of California, Riverside, and co-director of the sports medicine fellowship at Kaiser Permanente. “I am really not convinced the benefits go at all beyond traditional muscle massage, which can be helpful.”

Others voice similar reservations. “There’s no way to target or work the fascia without also working the muscle and ligaments and tendons,” says Tiffany Field, PhD, director of the Touch Research Institute at the University of Miami.

Field conducted a 2017 review of the research on massage and its health effects. She found that moderate-pressure massage triggers a “relaxation response” that may reduce depression, anxiety, pain, and heart rate. Imaging studies have also shown that massage changes the activity in brain regions associated with stress and emotion regulation. Pretty much all the benefits associated with fascia therapies are also linked with massage.

“When you move or press on the skin” — whether through massage, Rolfing, foam rolling, or even yoga and stretching — “you stimulate pressure receptors under the skin, which increases vagal activity, which leads to this whole cascade of bioelectric and biochemical events,” Field explains.

The “vagal activity” she mentions concerns a system of nerves — known collectively as the vagus nerve — that both gather information from the body’s organs and help control many of its autonomic functions, including stuff like heart rate, breathing, and the fight-or-flight response. Field says that increasing vagal activity can increase levels of circulating serotonin, which she describes as a one of the body’s natural anti-pain and anti-depression neurochemicals. “Increased vagal activity also leads to a decrease in stress hormones — namely cortisol — which can enhance immune function, and therefore health,” she adds.

Field’s point is that most fascia therapies probably work — though not for the reasons many practitioners claim. Rather than remodeling or stretching injured fascia, these treatments — like a massage — trigger neurochemical and nervous system shifts that produce the observed health benefits, she says.

There’s research backing her up on this.

While some sports-related conditions have long been blamed on fascia tightness or thickness, some recent efforts to confirm this link have come up short. Also, a 2014 study on self-myofascial relief found that using a foam roller after exercise could significantly reduce muscle soreness and pain. But here’s the twist: The authors of that study found that rolling one leg could trigger all these benefits in the opposite leg. Rather than loosening or reshaping the fascia, the study suggests that “there is a central nervous system component to the reduced pain,” says David Behm, PhD, co-author of the study and a research professor at Memorial University of Newfoundland in Canada.

“There are all these fancy names or concepts people create to make their protocol sound unique,” Field says, referring to fascia-targeting treatments. But the evidence to date suggests these may be no more effective than simple, do-it-yourself foam rolling, yoga, or plain old massage.