<sub>While leg lifts, certain ab exercises, and even hula hooping can all help work the hips, the hip flexors can still be a tricky part of the body to stretch Kinetics of hula hooping: An inverse dynamics analysis. Cluff, T., Robertson, D.G., and Balasubramaniam, R. School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada. Human Movement Science, 2008 Aug; 27 (4): 622-35.. To get them even stronger and more flexible, try these five simple hip flexor stretches:
4. Just swing it. For the front-to-back hip swing stretch, lie on the left side with hips stacked, propped up on the left elbow. Bend the left leg to a 90-degree angle and raise the right leg to hip level with toes pointed. Keep abs tight and swing the right leg all the way in front, then swing it all the way to the back, squeezing the booty along the way. Switch sides.</sub>
^{The only activity performed on a regular basis that fully extends the hip is walking and running. Hence as activity levels decrease so does the ability to extend the hip. This results in compensatory pelvic tilting and lumbar extension, with a reduction in the ability to accommodate uneven ground, negotiate obstacles, or attempt to change walking speed quickly. The compensatory pelvic tilt that accompanies tight hip flexors also predisposes the individual to  postural problems and back pain. Hip stretches done on a regular basis can help you maintain extension range of motion and thereby improve function.}
Since the hip flexors are so easy to overuse and strain, it is important to stretch them before exercise or strenuous activity. Because of their connectedness to other muscle groups in the legs (like the quadriceps), it is important to stretch the muscle group as a whole, not individually. This ensures that the entire area is warmed up and ready for the strain of exercise or activity, not just one or two individual muscles.
Bony encroachment: Any condition that results in movement or growth of the vertebrae of the lumbar spine can limit the space (encroachment) for the adjacent spinal cord and nerves. Causes of bony encroachment of the spinal nerves include foraminal narrowing (narrowing of the portal through which the spinal nerve passes from the spinal column, out of the spinal canal to the body, commonly as a result of arthritis), spondylolisthesis (slippage of one vertebra relative to another), and spinal stenosis (compression of the nerve roots or spinal cord by bony spurs or other soft tissues in the spinal canal). Spinal-nerve compression in these conditions can lead to sciatica pain that radiates down the lower extremities. Spinal stenosis can cause lower-extremity pains that worsen with walking and are relieved by resting (mimicking the pains of poor circulation). Treatment of these afflictions varies, depending on their severity, and ranges from rest and exercises to epidural cortisone injections and surgical decompression by removing the bone that is compressing the nervous tissue.
Coccydynia is an inflammation of the bony area (tailbone or coccyx) located between the buttocks. Coccydynia is associated with pain and tenderness at the tip of the tailbone between the buttocks. Pain is often worsened by sitting. There are many causes of tailbone pain that can mimic coccydynia including: fracture, pilonidal cysts, infection, and sciatica. Treatment methods include medication and rest.
If most inner-thigh openers feel too easy (and your ankles and knees are injury-free), try Frog Pose. Get down on all fours, with palms on the floor and your knees on blankets or a mat (roll your mat lengthwise, like a tortilla, and place it under your knees for more comfort). Slowly widen your knees until you feel a comfortable stretch in your inner thighs, keeping the inside of each calf and foot in contact with the floor. Make sure to keep your ankles in line with your knees. Lower down to your forearms. Stay here for at least 30 seconds.

These are really great tips. Just to imform my friends here, my cousin also gave me this link about some other techniches you can use. You have to know exactly what is going on in your body you know. the product is called Panifix, or "Unlock your hip flexor" which Gives You A Practical, Easy-to-follow Program You Can Use To Instantly Release Your Hip Flexors For More Strength, Better Health And All Day Energy. Proven Swipes And Creatives Here:https://tinyurl.com/yd6nbzfh 

The treatment of hip pain depends on the precise cause of the pain. Treatments can include rest, non-weight-bearing, cold application, and anti-inflammatory medications. For local inflammation, sometimes injection of cortisone medication (steroids) is used to quiet the inflammation. If infection is present, antibiotics are used. Fractures can require treatment with surgical repairs, including pinning, plates and screws, and total joint replacement. For severe arthritis, total joint replacement is performed when possible.
The problem is that these muscles aren't designed to be prime movers—they're designed to support the action of the glutes. Inability of activating the glutes can result in low back pain (low back muscles compensating), hamstring strains (overacting hamstrings), hip pain (resulting from hamstring-dominant hip extension) and knee pain (poor glute medius strength).
Poor Sitting Posture: The correct position of your low back should have a slight forward curve called a lordosis. When you sit slouched, this lordosis straightens out-or even worse-reverses itself. This loss of the forward curve in your spine can cause increased pressure on the small shock absorbing discs in your back. This increased pressure can displace your discs and lead to low back pain. Your physical therapist can teach you the proper way to sit to decrease, eliminate, or prevent your back pain.
In this study, one patient with sciatica was sent for ten MRIs, which produced 49 distinct “findings,” 16 of them unique, none of which occurred in all ten reports. On average, each radiologist made about a dozen errors, seeing one or two things that weren’t there and missing about ten things that were. Yikes. Read a more detailed and informal description of this study.

To avoid hip flexor pain, you should pay more attention to these muscles, Dr. Siegrist explains. When you are seated, your knees are bent and your hip muscles are flexed and often tighten up or become shortened. “Because we spend so much of our time in a seated position with the hip flexed, the hip flexor has the potential to shorten up. Then, when you are in a hurry because you are running to catch a bus or a plane, or you trip and fall, the muscle could become stretched. Here’s this stiff, brittle muscle that all of a sudden gets extended, and you could set yourself up for strain or some hip flexor pain.” Click Here to Learn Unlock Hip Flexors