A workout can be traumatic for the muscles. The most targeted are indeed often riddled with tiny tears. How to repair the damage? A recent study lifts the veil on a previously unknown mechanism.
Skeletal muscles are muscles under voluntary control of the central nervous system (unlike cardiac muscle). These structures are made up of hundreds or thousands of thin, tubular cells called “muscle fibers,” each containing functional contractile units called sarcomeres that contract and lengthen during exercise.
Eccentric contraction, where your muscles forcibly lengthen as they contract (during a bicep curl or downhill run, for example), can lead to overstretching of these sarcomeres, resulting in the formation of tiny tears . How to repair these wounds?
We know that damage caused by external injury can be repaired by muscle stem cells. These fuse with injured cells or create entirely new myofibers.
When it comes to exercise-induced injury, previous studies have this time shown that various proteins form a "cap" over the damaged region of the membrane some mere seconds after the trauma, while nearby mitochondria (powerhouses of the cell) help absorb any excess calcium that entered the cell through the tear.
In a new study published in the journal Science, a team describes an alternate process for repairing these injuries induced by exercise, this time involving the nuclei of muscle cells.
For this work, the researchers placed adult mice on a downward-inclined treadmill. They then sampled muscle fibers after their sessions. They did the same thing with about fifteen human volunteers, taking fibers from the vastus lateralis, located in the quadriceps femoris muscle.
In mouse and human subjects, researchers found that within five hours of the end of exercise, cell nuclei rush to the tears to issue "commands through mRNA molecules (kinds of genetic instruction manuals, so that new proteins are built to seal wounds). In just 24 hours, this repair process was "mostly done" , according to the study.
In the future, we might as well support on this new knowledge to develop new treatments capable of targeting molecular pathways allowing nuclei to migrate and initiate this repair process . In this way, doctors could therefore help to speed up the recovery of patients after muscle injuries.
