Curl-Up: Lie on the floor with your hands alongside your body, palms flat, knees bent and feet on the floor. Contract your abdominals to slowly curl one vertebra at a time off the floor, bringing your upper body up as high as you can while keeping your lower back in contact with the floor, then lower yourself under control to the start. Your hands will move alongside you as you rise up. Repeat for reps.
Leg Raise: Start with your hands alongside your body, your back flat on the floor, and your legs together and held about two inches off of the floor. Slowly lift both legs upward to a point just before they reach perpendicular to the floor, then lower them back to a point just before they touch down before beginning the next rep.
Alternating Sit-Up: Lying on the floor, knees bent and feet flat, place both of your hands lightly behind your head. Crunch upward as you twist your body, bringing your right elbow toward your left knee. Lower yourself back down, then bring your left elbow toward your right knee and lower yourself to start again. Once to each side equals one rep.