This exercise works on switching from a slow eccentric contraction, to a fast and force full concentric contraction. The body will be forced to create a large amount of force in a short amount of time. A good variation for this exercise is to have the athlete close their eyes. This makes it harder to time when the dumbbell will touch the ground.
Starting position: Stand upright while holding one end of a dumbbell with both hands. The dumbbell will hand with the free end facing downward.