Leg lifts, from a horizontal or vertical position, strengthen and tone your abdominals. Since your hip flexors -- which are on the top of your thighs -- dynamically contract as you raise and lower your legs, the abdominal contraction is isometric. When the rectus abdominis, RA, isometrically contracts, it does not shorten, but it statically tightens to stabilize your torso during the movement. The RA, the obliques and the transverse abdominis are challenged by leg lifts when you are lying or hanging as you raise bent or straight legs.
Whether you perform ab workouts daily or two or three times a week, leg lifts can be included into your abdominal exercise routine. Warm up your torso for five to 10 minutes with a light cardio exercise such as walking or rowing using a light resistance. If you perform leg lifts at the end of your strength-training workouts, you're already warm and do need to do a separate warm-up. Keep your stomach tight throughout your leg lifts by pulling your navel toward your back to support your upright posture and strengthen the transverse abdominis, which is the deepest abdominal muscle. Begin with one or two sets of 10 to 12 lifts and gradually increase to three sets. Rest between each set for approximately 30 to 60 seconds.
If you are a beginner, start your leg-lift workout in a lying position to target your rectus abdominis. Lie face up on an exercise mat or on a flat bench. If on the bench, grasp the sides of the bench over your head to help prevent a fall. You have two workout intensity options. The first is to bend your knees and place your feet flat on the floor or bench. Exhale and raise your knees toward your chest. Lift your legs as high as possible into a position that potentially raises your hips off the floor. Inhale and return to the starting position before you repeat. The second version uses straight legs. Straighten your legs and keep your feet and knees close together. Exhale and raise your legs toward your chest. Aim to raise your legs until they are straight up from your hips, but you can go beyond that or raise your hips if needed to create abdominal fatigue.
Perform vertical leg raises from an overhead bar or from a captain's chair, which consists of a tall chair back and arm rests but no seat. Position your back flat against the pad of the chair and rest your forearms on the padded bars. If using an overhead bar, grasp the bar with your hands at shoulder-distance apart and face your palms forward. From the chair or the bar, straighten your legs so they are hanging directly beneath you. Keep your feet and knees close together. Exhale, bend your knees and raise your legs toward your chest. Avoid swinging as you do this. Inhale, lower your legs and straighten them to the starting position. Repeat for your desired number of repetitions. Increase the intensity of your leg lifts by raising your straight legs toward your chest. Lift your legs as high as possible -- without causing back discomfort -- to strengthen your rectus abdominis.
When the vertical straight-leg raises no longer feel like a challenge and do not create abdominal fatigue, add resistance to your bent-knee raises. Place a dumbbell between your feet and hang your legs beneath you. Bend your knees and raise your legs toward your chest. Aim to raise your legs as high as possible. To further target your obliques, instead of raising your legs straight in front of you, lift your legs in a circular motion. For example, hang with your legs beneath you and then raise your legs to the right. Continue to raise your legs until they are in front of you and then lower your legs to the left until you reach the starting position. Complete the same number of circular leg lift repetitions in each direction.