HOW: Start on your back with your legs spread and both knees bent, bend the knee in which you want to bias more - meaning that heel is closer to your butt. Tighten up your stomach first, then your glutes. Next, drive your heels into the ground and lift your hips up towards the ceiling. At the end position your knee, hip, and shoulder should be in one straight line. Hold the end position and squeeze the glutes, then slowly return to starting position. The leg of the knee bent more should be working harder here.
FEEL: You should feel your glutes work to control this motion, particularly of the leg you are biasing. At no point should you feel your low back muscles doing the lifting motion.
COMPENSATION: Avoid arching at the low back as you perform this.
