Now in our body we have many of these motor units. Now, whenever we're carrying out an activity that basically requires a very small force, we only use several or few of these motor units. But if we're conducting some activity that requires a large force we have to use many of these motor units. And motor units can basically work together to carry out a motion in a coordinated and smooth fashion. So many different motor units can work together to create smooth and coordinated motion. If a certain activity requires a small force, a small number of motor units are actually used.