For a slim, firm midsection, perform exercises that will train all your abdominal muscles together. This move is challenging, so a few good repetitions are all you need to tone your torso muscles. Start with an easier version by lifting only one leg at a time; this will give you a chance to learn how to recruit the correct muscles without straining your back.
1 Lie face up on a mat or a level, padded surface. Extend your arms overhead and stretch your legs out in front of you parallel to each other. Inhale, lengthening your neck away from your feet.
2 On an exhale, press your navel down toward your spine, tighten your abdominal muscles and slowly raise your head, neck, shoulders and legs (or one leg) off the floor. Maintain this lifted position, keeping your upper arms near your ears and your legs in the air. Focus on feeling a deep contraction in your abdominal muscles, and don't let your back arch up away from the floor. Repeat three times, holding the peak of the contraction six to 10 seconds.
— Karen Voight