Big 5 - Lunge
In case you hadn't noticed, the hip moves in a few different directions. During movement in the saggital plane, the bottom of the squat is end range flexion (closing the angle of the hip), thus the trailing leg of the lunge is extension (fully opening the hip). This would be considered normal range of motion. When a joint doesn't have full range of motion, chances are it will be problematic. (The underlying principle of this whole series of blogposts - https://movementandmobility.wordpress.com/2015/06/01/the-big-5-introduction/)
The same Ol' story
Whenever a joint that's designed to articulate to create large amounts of movement doesn't, a joint that isn't suppose to move much does, in a compensatory manner. Compensation is like the ripple effect of throwing a stone in a pond. The joint that isn't moving is the stone hitting the water. It deflects movement to the structures above and below it creating movement elsewhere, the problem being that some joints don't like large amounts of movement (more so under load).
An example of this relative to hip extension (the lunge shape) is what happens during walking and running. Specifically what happens to the spine when the hips don't have their full potential to perform the movement available.
This picture shows you what happens when the vertebral joints of the spine compensate for the hip.
- The picture on the left is when you're standing in a neutral position
-The middle picture is when you have full capacity of the hip, you can see how the femur moves behind the torso without affecting the position of the pelvis or spine.
- In the picture on the right you can see the hip doesn't have the ability to move into extension. Instead of the head of the femur moving inside the acetabulum of the hip (the ball and socket joint), the femur and the pelvis move as one fixed structure dragging the vertebrae of the spine with it.
It's easy to see how there is potential for back pain during movements like running, especially when the lumbar spine is being compressed during repetitive flexion and extension motions. You might think that walking and running are just body weight movements and there isn't much load acting on your body, but the force of gravity can be brutal when your alignment is out.
Note - There are/could be numerous factors at play when a joint has reduced range of motion. 'Stretching' muscles to improve range of motion is just one angle to approach the problem, but one that you're responsible for.
So um, in English
If the tissues around the front of your hip aren't moving as they should, you won't be able to get your leg behind your hip without affecting your spine. There's only so much shit your spine will put up with before it decides it doesn't want to do the hip's job anymore. It will tell you this in the form of some kind of pain, however pain is probably just the symptom; it's some form of cry for help.
What to do
If you're like a decent chunk of the population of the planet you've probably been strapped to a chair from the age of five until 18/21/ongoing, depending on when you finished your education/what you do for a job. All you have to do is get into a position that looks like the opposite of sitting in a chair.
- Set yourself up against a wall or in the corner of a couch
- Squeeze your butt to create a slight posterior pelvic tilt
- Apply some tension by pulling yourself upright
- Make sure you keep your butt and abs tight, when you move you're a straight line that pivots from your knee
- Hang out here and try to accumulate some time (breathing is pretty important, so don't forget to do that)
* Don't just over extend your spine like I am below, this is exactly the same thing as what I was explaining in the first half of the post re: compensation of the spine
You could even be super awesome and come up with some sort of rule for yourself, for example - For every hour you spend sitting, you spend 5 minutes in this hip extension shape!