The sartorius muscle, located in the front of the thigh, is the longest muscle in the human body, according to Susan Hall, author of "Basic Biomechanics." It attaches to the iliac spine of the pelvis, runs diagonally across the front of the thigh, crosses the inside of the knee, and reattaches to the tibia bone of the lower leg. The sartorius assists other muscles with hip abduction, flexion and outward rotation. Strengthen the sartorius muscle by performing resistance exercises through various ranges of motion.
The exercises known as "Frankensteins" strengthen the sartorius muscle through hip flexion. Perform the exercise with your body weight only or while wearing ankle weights for added resistance. Stand with your feet about shoulder-width apart and toes directed forward. Flex your left hip and bend your knee to 90 degrees until your upper leg is parallel to the ground at waist height. Without rotating your right leg, cross your left knee across your body as far as possible, and then reverse by opening your left hip, so your knee points sideways away from your body. Replace your left foot back on the ground and repeat the exercise with your right leg. Perform five to 10 repetitions on each side.
Side-Lying Hip Abduction
This exercise strengthens the sartorius through hip abduction. As with Frankensteins, use your body weight only or wear ankle weights. Lie on your right side with your legs stacked and ankles flexed to 90 degrees, so your toes point forward. Rest your head on your right arm and left arm on top of your body. Keeping your toes pointed forward, lift your left leg straight upward to create a 6- to 12-inch gap between your legs. Slowly return to the starting position and repeat. Perform the exercise with your right leg as well.
Supine Hip Flexion
Like Frankensteins, the supine hip flexion exercise strengthens the sartorius muscle through hip flexion. Attach one end of a resistance band to a sturdy object, close to the floor, and tie the other end around your left ankle. From a seated position, slide away from the object to remove slack from the band, then lie on your back with your legs extended and heels on the floor. Lift your left foot and draw your knee toward your chest as far as possible to stretch the band. Slowly return to the starting position and repeat. After performing the desired number of sets with your left leg, tie the band around your right ankle repeat the exercise with your right leg.