Alternate Crunches: Lie on back, knees bent, and one leg crossed over the opposite knee at the ankle. Place the opposite arm behind the head and rest the head on the hand. Alternate right elbow towards left knee keeping the lower back stable against the floor. Do not pull on your neck, exhale when you are crunching in and keep abs slightly flexed as you return. Repeat for 12-25 reps or at your own pace then switch sides.