Researchers have created contracting muscle implants that can mimic some of the benefits of exercise, including improving muscle mass, strength and bone density while also slowing age-related muscle changes¹.

The research, published in Nature Aging on 26 August, is still a proof of concept, but if translated from animals into people, it could help to prevent muscle loss caused by ageing, chronic medical conditions and being bed-ridden, say the authors.

Muscle wasting affects many people, particularly older individuals, but there are no good solutions for the condition apart from exercising, says Shyh-Chang Ng, a co-author of the study and a biologist at the Institute for Stem Cells and Regenerative Medicine in Beijing. “But the people who need to do exercise the most often turn out to be the people who are unable to exercise,” he says.

Using a muscle graft to mimic exercise response is an intriguing premise, says James White, a physiologist at Duke University in Durham, North Carolina. However, people would probably need multiple muscle grafts throughout the body to achieve the benefits seen in mice. For those who are frail, bedridden or older — the very people who would need these grafts — undergoing several invasive procedures would be undesirable, White says.

Muscle-cell graft

To create the implants, called myografts, the researchers extracted stem cells from the quadriceps muscles of mice. They then isolated and cultured the stem cells in the laboratory to grow muscle cells. These were injected under the skin on the animals’ backs, with each mouse receiving its own cells to stop the immune system from rejecting a foreign graft.

The transplanted cells formed organized muscle tissue near the injection site, which contracted continuously and developed blood vessels. The grafts survived for several months before the researchers collected tissue samples to study.

They found that adult mice between eight and ten weeks old with myografts developed thicker muscle fibres than did control animals that did not receive myografts. Their muscles also showed changes that suggested reduced inflammation and fat accumulation.

In separate experiments in older mice, about 1.5 years old, the animals also had a higher proportion of lean mass eight weeks after transplantation than did mice that did not receive the myograft. After 15 weeks, animals with myografts also had higher bone density than controls. Older mice with grafts also performed better in tests of physical function; they ran farther and had greater grip strength.

More than just muscle

The researchers also fed a separate group of mice a high-fat diet to induce obesity. After 16 weeks, the myografted mice had a higher proportion of lean mass and a lower proportion of fat mass than did the control animals. They also had lower blood-glucose levels and reduced increases in cholesterol.

The treatment was also associated with lower signs of systemic inflammation — such as lower white-blood-cell counts. Other effects included lower triglyceride levels, reduced liver damage and higher energy expenditure compared with control mice. Myografts were also linked to improved cognitive benefits in older mice. In a maze test, mice with implants spent more time exploring unknown sections of the maze than did mice without the grafts, says Ng.