The theory is that when you rapidly descend into the “hole” of the squat, there will be a reflexive contraction of the muscles that primarily extend the knee. This will act as some sort of muscle trampoline and will allow you to reflexively contract your way to a completed rep.
Many people refer to the stretch reflex as the key to explosive training. How it is applied, however, is frequently misunderstood. This article takes an in-depth look at this action and how you can better utilize it in any or all aspects of your training.