The hands-on practice of massage has been helping to heal sore muscles throughout human history. And several modern studies support the use of massage to soothe body aches and pains. But how does it work? A new study from researchers at Harvard’s Wyss Institute for Biologically Inspired Engineering may have found the answer.

Skeletal Muscles and Mechanotherapy

Researchers know that immune cells, the cells of your body’s defense system, play a role in the skeletal muscles’ response to injury. Skeletal muscles are the muscles you use to move your bones. To search the link between muscle repair and the immune system, the research team studied the effects of compression and stimulation on damaged muscles in mice. This type of muscle massage is called mechanotherapy.

In their study, which is published in the journal Science Translational Medicine, the team caused muscle damage in the hind legs of mice by injecting the leg muscles with a substance called myotoxin. To treat the damaged muscles with mechanotherapy, the team developed a robotic device that would compress the muscle at a pressure and rate that could be measured and regulated. At the same time, the team used ultrasound imaging to measure muscle regeneration and repair.

No More Inflammatory Substances, No More Pain

Two groups of mice received the myotoxin injections, but only one group received mechanotherapy. The researchers discovered that muscle repair was faster and stronger in the mice receiving 14 days of mechanotherapy. The reason is that mechanotherapy compressed inflammatory cells called neutrophils out of the muscles, which improved the muscles’ ability to heal and regenerate muscle cells.

Neutrophils are the body’s way of removing germs and damaged tissues. They release inflammatory substances called cytokines and chemokines. The research team showed that neutrophils help in the early stages of muscle damage, but the inflammatory substances interfere with muscle repair and regeneration.

Neutrophils and inflammatory substances were lower in the treated muscles than in the muscles that were left to heal on their own. To confirm the removal of neutrophils during mechanotherapy, the team injected tiny fluorescent molecules. The researchers could witness these molecules vacating the muscle fibers during mechanotherapy. They also grew muscle tissue in the lab and observed the effects of neutrophils on a molecular level.

Soon after a muscle injury, the neutrophils stimulated the growth of cells called muscle progenitor cells, but the inflammatory substances released by the neutrophils slowed down the growth of the progenitor cells into fully active muscle cells. When the team analyzed muscle fibers in the treated and untreated mice, they found that the mice who received mechanotherapy were able to grow larger and stronger muscle fibers than the untreated mice.

The team would like to continue their research in larger animals and eventually in humans. This could lead to mechanotherapy devices that would treat injured muscles, improve muscle performance and may even treat age-related muscle loss, bringing the ancient art of massage into the twenty-first century.

For more information on how massage can relieve pain: Visit the National Center for Complementary and Integrative Health website at

Source: Studied titled “Skeletal Muscle Regeneration with Robotic Actuation-Mediated Clearance of Neutrophils,” by researchers at Harvard’s Wyss Institute for Biologically Inspired Engineering, Boston, published in Science Translational Medicine.

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