At the hip joint, your pelvis and femur -- the largest bone in your body -- join together. Many different muscles cross this important joint, allowing you to sit and stand, walk, cycle, run, and perform other movements. Your hip flexor muscles consist primarily of the rectus femoris -- one of the quadriceps on the front of your thighs -- and the iliopsoas, which is actually a group of muscles that includes the psoas major, psoas minor and the iliacus. Together, the hip flexors flex your hip, bringing your thighs and torso closer together.
Hip flexor exercises also work your abdominals. The decline sit-up, for example, targets your lower abs and hip flexors simultaneously. To do these, hook your lower legs under the supports on a decline bench and lie face-up with your hands on the sides of your head. Keeping your back as straight as possible, lift your torso off the bench and come to an upright position. Slowly lower yourself back down and repeat. To increase the resistance with this exercise, hold a weight plate or medicine ball against your chest.
Leg lifts work your hip flexors and lower abs from a position on your back. Lie on the floor, place your hands at your sides and lift your legs up until they form a 90-degree angle to your body. Slowly lower them back down, stopping just short of the floor. Repeat. If you feel stress on your lower back, place your hands under your tailbone. For a more taxing exercise, wear ankle weights. You also can ask a training partner to wrap a rubber resistance band around your lower legs and pull against your legs.
Inner Hip Flexion
This standing inner hip flexion exercise requires an ankle strap--it's performed on one side of a cable machine. Fasten the strap to your lower right leg and stand with your back facing the weight stack. Your right leg should be behind your body at this point. Lift your foot off the floor and pull your knee up in front of your body until your thigh parallels the floor. Slowly lower your leg back to the starting point and repeat. After doing a set of reps, switch sides.
Knee crunches work your hip flexors with the aid of an exercise ball. After placing your hands shoulder-width apart on the floor, position your shins on top of the ball and lift your hips to get your back straight. Steadily tuck your knees into your chest as you roll the ball on the floor. Extend your legs back out and repeat.
Elbow Instep Lunge
Elbow instep lunges work your hip flexors, thighs and glutes at the same time. To do these, stand with your feet together and arms at your sides. Take a step forward with your right foot and lower yourself into a lunge by bending your knees. While you do this, lean forward, place your left hand flat on the floor and your right elbow on your right thigh. Slowly step back to the starting position and repeat with your other leg. Alternate back and forth with each leg. Don't let your back knee touch the floor when you're lunging. For a more challenging variation, touch the floor with your hand instead of placing your elbow on your thigh.