The lower abdomen is mostly the rectus abdominis muscles. These muscles are long and flat and most exercises targeting this area are done from a supine, or face up, position. Perform each exercise for one to three sets and eight to 12 repetitions. Be sure to take at least one day of rest in between exercises to allow adequate time for muscle repair.
Begin face up on the floor with your knees bent and aligned over your hips. "Shape" recommends keeping your calves parallel to the floor and your knees and ankles together. Then contract your abdominals and bring your spine to a neutral position.
Slowly lower your right foot so your toes barely touch the floor. As you lift your toes off the floor, exhale and return your legs to the starting position. Repeat, alternating sides. Each leg counts as one set.
Seated Leg Circles
"Women's Health" lists this exercise as a top way to flatten the lower belly. Begin by sitting on the floor with your legs fully extended. Then lean back on your elbows, keeping your fingers cupped at the sides of your hips. With your lower back pressed into the floor, engage your core and lift your legs about 45 degrees. Point your toes while pressing your thighs together and trace clockwise circles. Perform eight to 12 circles. Then switch to counterclockwise circles. Each direction counts as one set.
Lie in a supine position on a mat with your knees bent and feet flat on the floor. Your arms should be next to your sides with your palms facing down. As you exhale, stiffen your torso by contracting your abdominal muscles and slowly lift your feet off the floor. The American Council on Exercise explains to keep your knees directly above your hips while maintaining a 90 degree angle in the knees. Then contract your core and hip flexor muscles and slowly raise your hips off the mat. Roll your spine up as if trying to bring your knees toward your head and curl up until your spine cannot roll any further. With an inhale, lower your spine back toward the mat by moving your upper thighs backward until they are positioned directly over your hips. This counts as one repetition.