Maybe you’ve seen people practicing tai chi in a park. Feet planted firmly on the ground, they lift their arms together, toward the sky, and then break them apart at the peak, slowly bringing them back to their sides. They lunge, moving in slow dancelike movements, concentrating on steady breathing.

But what you can’t see is perhaps the most impressive takeaway from this ancient Chinese martial art: what’s happening on the inside.

Researchers from Tufts University in Boston have found the practice of tai chi is effective in easing fibromyalgia, a disorder often characterized by widespread muscle pain. In fact, tai chi was more effective than many other exercises that are recommended for the disorder.

About 11 to 69% of patients with fibromyalgia report using opioids. Usually, patients will use aerobic exercise to ease the pain, but many have trouble following a regular exercise plan.

In the Tufts study, more than 200 people were split into different exercise groups. Those in the tai chi class attended 62% of the sessions, while those in the other aerobic exercise group attended 40%. Those who practiced tai chi weekly or biweekly for 24 weeks showed significantly more improvement than those who practiced for 12 weeks.

Originating in Chinese traditional medicine, tai chi integrates multiple elements, like physicality and spirituality, to promote health using low-impact movements and minimal side effects. As a practice meant to help people grow in their mental states and fitness levels, it just might be a solution for patients who want to ease their pain, long after leaving the park.