Circuit 2, Exercise 2: Lateral Lunge With Knee Drive
Start standing tall with your feet about hips width apart.
With control, step your right leg out to the right coming into a lunge. Your left leg should be straight and there should be a bend in your right knee.
With most of your weight on your right leg/foot, push through your right heel as you simultaneously drive your right knee up and off the ground, returning to a standing position. Keep your foot flexed (don't point your toes down).
If this is too hard, you can return to the starting position and then lift your right knee up. Be sure to keep a 90-degree angle at the right knee and right hip — this is the part of the exercise that fires up your abs.