Most people think force comes from the ground. On the contrary, we put force into the ground and the ground reads the force. When you punch a punching bag at the arcade, does the force come from the machine or from you hitting the punching bag? Obviously from you punching the bag. Force in the ground is no different. We put force INTO the ground, and the force plates read force from the ground.
WHY IS THIS IMPORTANT?
Our energy comes from our upper body wedging our legs down into the ground. Our legs do not create the energy. Do you jump up in the air by bending your legs by taking your chest down to your knees? Go ahead and try it. Good luck, jumping very high without taking your chest down first. When we force ourselves to control our body from the top our legs find balance down below.