Similar to yoga's Warrior 3, this exercise fires up your core by challenging your balance. As you move in and out of the pose, you will be working the back of your body too. Stand with all your weight in your left foot, abs engaged and chest lifted. Reach your torso forward as you lift your right leg behind you. Reach your arms overhead for balance as your torso and leg come parallel to the floor. Hold this position for a moment, and reach through your right heel to engage the back of the right leg. Moving in one piece, lower your right leg toward the floor as you return to standing upright, resting the right foot lightly on the ground. This completes one rep. Do 10 reps before switching sides; and do two to three reps.