for those people who may not know about drop squats, this is from kelly b site:
reactive squat- In this variation the focus is just as much on the negative eccentric contraction as it is on the "jump". Hold the weight tight against your shoulders and drop quickly from top to bottom. Focus on accelerating during the negative (down) phase so that you build up a lot of mechanical tension during the eccentric to concentric switch that occurs at the bottom. Your hips will get fairly low, somewhere around parallel. When getting started, think of finding the point where you get stretch reflexes from as many muscle groups as possible (glutes, hamstrings, quads, calves, etc). Get low enough to accomplish this. After you relax and free fall you then quickly gain full tension to stabilize the force of the load at the bottom.
This will develop explosive power in the entire lower body musculature and teach you to really turn on the power. If all is done correctly you should feel your body want to rebound to the top after the initation of force absorption at the bottom. You should feel your body respond with a reflexive "bounce" at the bottom. It can be beneficial to just focus on the negative part with lighter loads until you get the hang of the movement. Once you do, simply carry the reflex out of the bottom all the way to the top and jump. Reset yourself for each repetition. The loading on this variation will be between 30-60% of max squat depending on the goals and needs of the athlete. The rep range will fall between 3-10 per set.