Tight hip flexors occur for a variety of reasons. Those who run frequently or engage in other activities that put strain on the hip flexors are likely to experience hip flexor tightness at one time or another. A blow to the hip or poor conditioning can also be causes of tight hip flexors. These causes can usually be attributed to tiny tears that occur to our hip flexors through rigorous activity.
When I do a deep knee bend like a sumo squat I get a popping in the outside of my left knee. It feels like a big tendon or ligament is slipping per something. It isn’t painful peer se but I’m afraid if I do it a lot it will be. Is that a relatively common symptom for a guy with tight flexors, it bands, etc? Should I just push through it or have it checked out?

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
Kneel with a wall or pillar behind you, knees hips-width apart and toes touching the wall. Arch your back to lean back while keeping your hips stacked over your knees. Take your arms overhead and touch your palms into the wall behind you. This bend does not need to be extremely deep to feel a great stretch in the hips and strength in the lower back.
Lucky for us, there are tons of different ways to stretch hip flexors. We’ve put together a broad selection of some of the most popular tight hip flexor stretches below. Some of these stretches may work better for you than others, and there’s also many more hip flexor stretches you can try beyond these. So, experiment with all different kinds of stretches and decide which ones are best for your body.
Grade III (severe): A complete tear in your muscle that causes severe pain and swelling and you can't bear weight on that leg, making it difficult to walk. You've also lost more than 50 percent of your muscle function. These injuries are less common and may need surgery to repair the torn muscle. They can take several months or more to completely heal.
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