And this is exactly what happens when we exercise. So let's take a look at the following muscle cell. So this individual single muscle cell, single muscle fiber consists of many of these myofibrils found inside the cytoplasm of that muscle cell. Now these myofibrils basically are made up of adjacent units we call sarcomeres. And these sarcomeres themselves are composed of meiosin and actin. Now when we continually exercise on a daily basis, what happens is we actually increase the number of myosin and the number of actin inside each sarcomere.