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. And that in turn increases the thickness, increases our diameter of each one of these myofibrils. And over time, because our thickness of each of these myofibrils is increased the entire thickness and diameter of the muscle cell will increase as well. And because it's the actin and the myosin that basically move along each other to produce our force, it's these that create the force in the first place.