HOW: Place a swissball on a wall and position the middle or small of your back on the ball. Lean into the ball while keeping your chest up. Walk your feet out and have them about shoulder width. From here, sit down like you're sitting in a chair going slowly on the way down, then push into the floor back up into the starting position.
FEEL: You should feel you glutes, hamstrings, and quadricep muscles working
COMPENSATION: Keep pressure against the ball the entire time.