The stomach muscles consist of the transverse abdominis, rectus abdominis and the obliques. Exercises for the abs should be done three days a week at least if you want to tighten them, recommends the National Academy of Sports Medicine (NASM). It's important to do exercises that work all these muscles so you can tighten your entire stomach area.
The bent-leg side crunch is an appropriate exercise for beginners and even seniors to use to work the oblique muscles, according to "Core Training for Greater Strength and Better Health" by Thomas Boettcher. The exercise is done lying on your side with your legs bent. This way you can raise your shoulders and ribcage toward your hips to engage your oblique muscles. If lying on your right side, raise your shoulders up to work your left oblique muscle. You can also raise your left leg to work your outer thigh and challenge the obliques even more. Arms can be crossed on the chest.
Free Weight Crunch Exercise
The free-weight crunch exercise is an intermediate/advanced exercise that targets the rectus abdominis, according to Boettcher's book. Beginners can make this exercise doable for them by leaving the free weight out of the equation. The exercise is done lying on the floor with a free weight held to a person's chest. Exercise plates are best because they are flat, and some have handles, but medicine balls or dumbbells may also be used. Legs can be straight or bent with the feet on the floor. The torso is lifted off of the floor about 30 degrees, just enough to clear the head and shoulders. The lower back is kept pressed down to engage more of the abdominal muscles and protect the lower back from strain accompanied with arching it off the floor. Both moving up off the floor and lying down should be done with smooth movements so momentum is not used.
The single-leg stand is an exercise that targets the transverse abdominis and also improves your balance. Your transverse abdominis muscle is a deep abdominal muscle that stabilizes your spine. All you have to do is stand on one leg and raise your foot about 3 to 6 inches off of the floor, recommends the American Council on Exercise (ACE). You have to stand up tall and keep your shoulders and hips level for the exercise to work correctly. As little as 10 to 15 seconds of holding the foot up is enough to work the abs. Holding your arms over your head and raising the lifted foot higher will increase the difficulty of the exercise. Closing of your eyes and tilting your head to one side will make the exercise the most challenging.