In the time of coronavirus an awful lot of people are not just working from home they’re also working out at home. That’s a good thing; exercise is a great way to boost the immune system, stay healthy and deal with stress. But for people used to more structured workouts at the gym it can come with a downside. Trying new routines at home that look easy on YouTube, but are harder in practice could potentially increase the risk of injury.

A new study from Japan looks at what happens when you damage a muscle. It won’t help it heal faster, but it will at least let you understand what is happening inside your body as you sit there with ice on your arm and ibuprofen in your hand.

The researchers found that when you damage a muscle, for example by trying to lift too much weight or doing too many repetitions of one exercise, the damaged muscle fibers leak substances that activate nearby “satellite” stem cells. These satellite cells then flock to the site of the injury and help repair the muscle.

The team, from Kumamoto University and Nagasaki University in Japan, named the leaking substances “Damaged myofiber-derived factors” (DMDFs) – personally I think “Substances Leaked by Injured Muscles (SLIM) would be a much cooler acronym, but that’s just me. Gaining a deeper understanding of how DMDFs work might help lead to therapies for older people who have fewer satellite muscle cells, and also for conditions like muscular dystrophy and age-related muscular fragility (sarcopenia), where the number and function of satellite cells decreases.

In an article in Science Daily, Professor Yusuke Ono, the leader of the study, says it’s possible that DMDFs play an even greater role in the body:

“In this study, we proposed a new muscle injury-regeneration model. However, the detailed molecular mechanism of how DMDFs activate satellite cells remains an unclear issue for future research. In addition to satellite cell activation, DMDF moonlighting functions are expected to be diverse. Recent studies have shown that skeletal muscle secretes various factors that affect other organs and tissues, such as the brain and fat, into the bloodstream, so it may be possible that DMDFs are involved in the linkage between injured muscle and other organs via blood circulation. We believe that further elucidation of the functions of DMDFs could clarify the pathologies of some muscle diseases and help in the development of new drugs.”

The study appears in the journal Stem Cell Reports.