These jumps are an explosive movement that really activates the glutes & other muscles in the legs, hips & core. Jump squats are one of the best to help strengthen the knee joint & help prevent knee injury. It is critical for an athlete to learn how to handle the forces applied to the lower body & core when jumping & landing. First, make sure you are doing these jumps on a surface that can provide some cushion when landing. As an example, land on rubber, artificial turf, or an exercise mat. No concrete. Start with feet hip width & hands held at chest height. Initiate the jump by taking the hips back first, then bend the knees to sink down into a mini squat. Take hands and arms back when descending in order to use them for getting a max jump. Spring up as high as possible using a good hand and arm thrust overhead as if to block a spike on a volleyball net. Absorb the landing with the ankles, knees and hips and with feet hip width. Do repeat jumps for the conditioning effect. Tip: Use arms & legs to jump & land light as a feather. Also avoid the "knock knee" position on take off and landing.