How to do it: Begin with a 20- to 30-inch box or bench right behind you. Straighten one leg and lift your foot in front of you, bend your standing leg, and push your hips back as far as possible as if you’re squatting on two legs, but just doing it on one. Continue until your butt hits the bench, pause, then squeeze your glutes and drive through your planted heel to stand up. Do not relax and release the tension in your muscles as you sit. Repeat this movement, alternating sides each time. (Once you master lowering to touch your glutes to the bench, lower the bench or try lowering to the floor.)
Apply the above concept to your hips. When you sit, your hips are in a "flexed" position. Therefore, the muscles that flex your hips are in a shortened state. You probably spend at least a third of your day sitting down. Think about how much time those hip flexor muscles stay shortened. A lot. Over time, they become tighter and tighter until you look like the old man in the picture. So unless you want to look like that, perform the stretches shown below.
Start kneeling on your mat with knees hip-width apart and hips directly over knees. Press your shins and the tops of your feet into the mat. Bring your hands to your low back, fingers pointing down, and rest palms above glutes. Inhale and lift your chest, and then slowly start to lean your torso back. From here, bring your right hand to rest on your right heel and then your left hand to your left heel. (If you can't reach your heels, turn your toes under; it will be easier to reach your heels in this modification.) Press your thighs forward so they are perpendicular to the floor. Keep your head in a relatively neutral position or, if it doesn't strain your neck, drop it back. Hold for 30 seconds. To come out of the pose, bring your hands to your hips and slowly, leading with your chest, lift your torso as you press the thighs down toward the floor.
If certain activities or overuse are causing hip pain, stop those that aggravate the discomfort and talk to your doctor. Excess weight can put pressure on the hip joint, so losing the pounds can provide relief and help you avoid further problems. Some causes of hip pain, such as fractures or hernias, may need surgical repairs. If your hip pain persists, talk to your doctor about the possible causes and treatments.
I think you should mention that for some people, stretching is not the solution and that it will deteriorate their posture. Some people need stretching, but most people I know need to strengthen their "overstretched" hip flexors. Many people can't do a single hanging leg raise. Check this site if you want to know more about the importance of hip flexors bit.ly/Unlock_Your_Hip_Flexor Report
Hamstring squeeze. Use the machine that works your hamstrings; you will either lie on your stomach or sit with a pad behind your knee. Push against the pad, moving your knee up toward the ceiling or backward (depending on which position you’re in). “In other words, bend your knees,” Pariser says. But to avoid cramps in your hamstring muscles, don’t bend your knee so much that your heels are too close to your buttocks.
A sedentary lifestyle can lead to having weak and tight hip flexors as they are always in the shortened position. Tight hip flexors can lead to a limited range of motion, poor posture, lower back and hip pain, and even injuries. These muscles need to get a workout when you are standing and doing movements such as raising your leg to climb stairs, run, or ride a bicycle.