Side-Plank Crunch Begin in a side elbow plank with your left elbow down and your right hand behind your head. Keeping your torso stable and your waist lifted, bring your right leg up toward your shoulder to lightly tap your right elbow. Lengthen your right leg back to the starting position to complete one rep. Do as many reps as you can in 15 seconds and then switch sides for another 15 seconds. Image Source: POPSUGAR Photography