The No-Weights Workout: Squats
When squatting, keep your hands behind your head and squat as deeply as you comfortably can. Contract your abs before you descend, keep your back straight, and squat deeply, as if sitting in a chair.
Make it Hard
When you reach the bottom of the squat, jump as high as you can. This makes the move explosive, adding power and honing your nervous system to improve muscle response.
With your feet shoulder-width apart, kick your right foot off the ground behind you and hold it. Drop into a squat. To make it more difficult, do a one-leg squat with your leg out in front of you, keeping it raised while lowering your body until your butt is about two inches off the floor.