Researchers at Washington University School of Medicine in St. Louis have demonstrated a new gene therapy that builds strength and muscle mass quickly while preventing obesity even when the recipient is eating a high-fat diet. This isn’t some crazy new bodybuilding tool, though, but rather something that could be used as a physical therapy aid for people with muscle-weakening arthritis or those suffering from osteoarthritis-related joint pain.

“We know that obesity and joint injury are the primary risk factors for osteoarthritis,” Farshid Guilak, professor of orthopedic surgery and director of research at Shriners Hospitals for Children in St. Louis, told Digital Trends. “However, in cases of severe obesity or muscle loss, it is extremely difficult — if not impossible — to lose weight or improve muscle strength through normal exercise and diet. The goal of this study was to show the importance of muscle strength in overriding many of the harmful effects of obesity on the joint.”

So far, the gene therapy approach has only been demonstrated in mice. The researchers delivered the gene for a molecule called follistatin to the muscle of eight-week-old mice, via injection. The protein blocks myostatin, a molecule normally responsible for stopping muscle growth. The mice in the experiment gained around twice their normal muscle mass and were able to completely burn off all the extra energy from an unhealthy high-fat diet. This prevented almost all the metabolic complications of obesity, such as systemic inflammation and high blood sugar, while also reducing arthritis and pain significantly.

The researchers worried that the gene therapy could potentially have a negative effect on the mice’s hearts. However, these fears proved unfounded and heart function in the mice actually improved, along with overall cardiovascular health.

“These first studies in mice have shown that the procedure has excellent efficacy and safety,” Guilak said. “The next steps will be to do longer-term studies in mice and possibly larger animals to ensure safety of this procedure.”

Guilak said that, should these steps prove successful, the researchers would consider testing the approach in humans — with the initial trials in those with severe, possibly life-threatening diseases of the muscles, such as muscular dystrophy.

A paper describing the work was recently published in the journal Science Advances.