The motion of moving the knee toward the chest is called hip flexion. Any time you "flex" a joint, you decrease its angle. Knee to chest exercises involve hip flexion with both thighs together or each thigh independently. From an anatomical standpoint, these exercises can be used for multiple applications -- most notably to build the abdominal muscles and stretch the lower back.
Captain's Chair Knee Raises
The captain's chair knee raise is heralded as one of the best exercises for the abdominal area. In a 2001 study commissioned by the American Council on exercise, the captain's chair caused over 200 percent mean activity of the rectus abdominis and obliques. To do the knee raise, align your body on the machine with your feet on the lower supports, back against the backrest and arms resting on the upper padded supports. Grasp the handles, remove your feet and let your legs hang straight down. Pull your knees up toward your chest in a steady motion. Squeeze your abs, slowly lower your legs and repeat.
Pregnancy Stretch
Being pregnant causes a lot of extra weight in the midsection. This in turn places stress on the lower back and can cause pain to flare up. A face down knee to chest stretch can offer relief for this pain according to the AskDrSears.com website. To begin, assume an all fours position with your knees directly under your hips. Slowly bend forward at the waist and place your forearms on the ground. Lightly place your head on your forearms as you move your chest toward your knees. Maintain this position for two to five minutes and slowly rise back up. If it will make you more comfortable, place one or two pillows under your arms.
Knee to Chest Stretch
A knee to chest stretch specifically targets the lower back and is performed from a face up position. The Mayo Clinic warns that you should not attempt this exercise if you currently have osteoporosis. To begin, lie on your back with your legs extended. Keeping your right leg still, lift your left leg, bend your knee and place your hands on your upper shin. Steadily pull your knee into your chest and hold for 20 to 30 seconds. Slowly release and switch sides. You also have the option of pulling both knees in at the same time.
Reverse Crunches
Reverse crunches work the lower abs and are performed from a face up position on the floor. To begin, lift your legs, bend your knees and place your arms at your sides. Steadily pull your knees into your chest and hold for a full second. Move your legs back to the starting position and repeat. To make this exercise more challenging, extend your legs out straight when you lower them down. If you feel strain on your lower back at any point, place your hands under your tailbone.
Bicycle Kicks
Bicycle kicks work the entire abdominal area from a face up position on the floor. To start out, lift your legs, bend your knees 90 degrees and level your shins to the floor. After placing your hands on the sides of your head, raise your shoulders off the floor so you are looking forward. Quickly move your right elbow and left knee toward each other as you extend your right leg out. Reverse the movement to target your other side, and continue to alternate back and forth.
References
- American Council on Exercise; New Study puts the Crunch on Ineffective Ab Exercises; Mark Anders; May/June, 2001
- AskDrSears.com: Kegels: Exercises for an Easier Delivery
- Mayo Clinic; Knee-to-chest Stretch; Mayo Clinic staff; February, 2011
- Fitsugar; No Equipment Necessary: Reverse Crunch and Double Crunch
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