The hip flexor is a group of muscles that attach your femur to your pelvis and lower spine. This muscle group allows you to raise your knee, and it's vital to walking, standing and sitting. But too much sitting can shorten the muscles of your hip flexor, leading to lower back pain and tightness in the hips. Yoga can help keep your hip flexor supple to prevent lower back pain and postural problems.

The hip flexor muscle group consists of a number of smaller muscles. They are:

• The psoas major and psoas minor, which attach your femur to your lumbar spine.
• The illiacus muscle, which attaches your femur to your pelvis.
• The sartoris and quadriceps, which attach the femur to the pelvis.
• The muscle tensor fasciae latae, which runs along the outside of the hip and thigh and attaches the femur to the pelvis.
• The pectineus, adductor longus, adductor brevis and gracilis, which run from the inner thigh to the pelvis.

Together, these muscles allow you to raise your knee towards your torso and lower it. They're also the muscles that allow you to move your legs from side to side. If these muscles become tight and short, you'll experience lower back pain, problems with posture and gait, and stiffness and inflexibility in the groin area.

Many people in today's Western society have short, tight hip flexors. The problem occurs due to a combination of factors unique to Western life. Western people lead sedentary lifestyles, sitting at desks all day, driving cars, sitting around dinner tables and watching television. While all this sitting doesn't have a noticable effect on the strength of hip flexor muscles, it can cause significantly decreased flexibility in this muscle group as they quickly become accustomed to remaining in the seated position.

Western society also encourages the use of chairs. In the past, many people didn't own large quantities of furniture, the way that modern Western people do today. Instead, people crouched, squatted, hunkered or sat on the ground; in Eastern countries, many people still behave this way. Chair sitting encourages tight, short hip flexors.

You don't have to give up your office job or your home furnishings in order to gain flexibility in your hip flexors. Do a few yoga poses that work on the hip flexors each day, and you'll quickly begin to see marked improvement in the flexibility of your hips and a decrease in back pain, as well as gait and postural problems.

Here are some yoga poses that can help stretch and lengthen the hip flexors:

• Warrior II and Triangle poses help to stretch the muscles of the inner thighs.
• Warrior I pose and Lunge poses (whether with the knee lifted or lowered to the floor) stretch the hip flexor muscles on the front of the thigh.
• Pigeon pose stretches the muscles on the back of the hip; it's important to balance out the lengthening of front hip flexor muscles with the lengthening of back ones.