Watch as Coach David Butler explains that in practice his athletes get 12 to 13 jumps. The key is that the jumps are of a high-quality, and they aren't focused on the quantity. When the quality of the jumps and technique starts to break down, that is an indication that their brain is starting to break down. When you see the technique starting to slide it is best to stop so that the athletes don't finish practice experiencing failure. Send them home and let them come back and jump another day.