This twist on the traditional plank will tone your abs and strengthen your core. Grab a mat, lie on your side and position your elbow directly under your shoulder. Stack together your legs, knees, ankles and feet. Tighten those abs, and push your elbow against the floor as you lift up your hips off the floor until your shoulder, hip, and foot are in a straight line. Reach up with one hand and extend. Rotate your torso downwards and reach under your body. Rotate back to the side plank with arm up and repeat for 10-12 times before switching sides.