Your thigh flexors are more properly known as your hip flexors. These muscles work any time you lift your knee or a straight leg, or do an old-fashioned situp. Because your hip flexors and lower-back position are closely connected, you should pay close attention to maintaining proper form when you exercise your hip flexors. In particular, beware of doing straight-leg raises, which can place excessive pressure on your lower back; instead, try variations on the bent-knee raise.
Captain's Chair
Step 1
Step into the captain's chair, facing out. The captain's chair resembles an elevated chair with padded arms and back but no seat, and is sometimes part of a VKR, or vertical knee raise, station.
Step 2
Place your forearms on the padded arms and grasp the handles, which jut up from the ends of the arms, to steady yourself.
Step 3
Bend both knees, lifting them slowly to about hip level.
Step 4
Lower your knees and extend your legs, squeezing your abs to stabilize your spine. Think of aiming your feet slightly forward and down, instead of straight down beneath your body. This completes one repetition.
Ring Knee Raises
Step 1
Adjust a pair of height-adjustable gymnastics-style rings, which you can suspend from any sturdy ceiling beam or ceiling-mounted pullup bar, until you can hang from them with your arms straight.
Step 2
Grasp the rings, palms facing in, and lift your feet off the ground. Think of drawing your shoulders back and down slightly as you hang, so your larger back and shoulder muscles support your weight, protecting your rotator cuff.
Step 3
Squeeze your abs, drawing your belly button against your spine as you draw your knees up to hip level, as you would when using the captain's chair. A slow, controlled movement is particularly important here because your hip flexors are stabilizing not just the weight and movement of your legs, but your body position on the rings, too.
Step 4
Keep your spine in neutral position -- think of continuously drawing your belly button toward your spine -- as you slowly extend your legs down and slightly forward of your hips. This completes one repetition.
Lying Leg Raises
Step 1
Lie flat on your back, knees bent and drawn in toward your chest. If you need extra stability, lie where you can reach over your head and hold onto a sturdy railing, a piece of furniture or any other solid anchor that won't move or fall on you when you pull on it.
Step 2
Extend both legs until they're straight, with your feet elevated slightly off the floor. The closer your feet are to the floor, the harder this exercise will be. Start with your legs at a 45-degree angle and slowly lower them as you build strength and endurance. Squeeze your abs to keep your lower back from arching. If you can't keep your lower back from arching, the exercise is too hard; raise your legs a little higher.
Step 3
Draw your knees back in toward your chest to begin another repetition.
