So let's suppose I take the following marker and I try to curl my hand. So I tried to basically raise the marker. I tried to exert a force that basically does work against the force of gravity which is pulling down on this marker. Now because the marker has a small mass that basically means I'm going to have to apply a small force to actually move this marker against the force of gravity. So that means because I'm going to have to apply a smaller force, I'm only going to have to use a small number of motor neurons. So let's suppose I'm only using motor unit number one, that involves motor neuron number one as well as these muscle cells that it actually innervates.