Ok… The hips! Your hip should be an extremely mobile joint. And it should be able to operate mostly independently from your spine.
This is really important when you extend your leg behind you. This action is known as hip extension. This should happen basically every step you take while walking or running.
When you walk your hamstrings and glutes should pull your hip back using your leg and foot as a lever to propel you forward. The problem comes when you don’t have enough hip mobility and your hip can’t extend far enough. Now your spine has to make up the difference.
This is a common problem and most people probably don’t even realize they’re doing it. But this mobility problem puts a lot of extra wear and tear on your lower back joints and muscles. Over time you will use your lower back muscles to walk when they should just be supporting your spine.
In order to release your lower back and eliminate the pain, you need to learn to use your hips correctly. This means restoring mobility through stretching and corrective exercises. You also need to learn to reintegrate all of your pelvic and hip musculature with practical movements like squatting and crawling.
If you don’t the address the underlying cause the problem will continue to worsen. Your hip joint will become even less mobile while your lower back continues to degrade through overwork.