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. Now instead, let's suppose instead of raising this marker I take some type of weight. And that weight let's suppose has a very large mass. So now because I'm trying to lift a very large mass I'm going to have to use many more motor units.