The Sarcomere

Sarcomeres are the microscopic structures in your muscles whose contractions do the actual work of flexing your muscles. Strings of sarcomeres called myofibrils are bound together into muscle fibers. When your sarcomeres contract, these muscle fibers stiffen and a force is exerted.

The contraction and expansion of each sarcomere also pumps blood in and out of it. This pumping keeps the sarcomere supplied with the oxygen and nutrients it needs to function.

Even when a muscle is fully contracted, no more than a third of all the sarcomeres are actually contracted. Sarcomeres can’t stay contracted all of the time, as they need to keep pumping blood.

Healthy sarcomeres enable a muscle to contract and expand fully. When a healthy muscle is completely relaxed, it’s supple and doesn’t pull on anything else in the body. But what happens when things go wrong?