Let’s take a moment to define two anatomical terms; extension and flexion.
Stand up and let your arms hang by your side. Now reach out in front of you as if to grab your steering wheel. This is flexion.
Let your arm hang by your side again. Now move the arm behind you, without twisting or turning. This is extension. When you walk with a good arm swing, your arm is moving from extension to flexion in this plane (back to front) that we call the sagittal plane.
The same can be applied to the legs. If you lift your leg out in front of you as if to climb a step, this is flexion (of the hip and if the knee is bent, the knee also). Standing on one leg, take the other leg behind you: extension of the hip. When you are walking, your leg moves backward and forward on the sagittal plane.
The amount of extension of the thigh bone (femur) can be measured by how many degrees the thigh can move in this direction, provided the pelvis remains neutral. Although if you watch someone walking it might appear as if their leg is moving behind them, If the pelvis tips forward when the leg moves back, the fulcrum is actually the lower back – precisely the place where back pain is commonly felt! There is less movement in the actual hip joint than there is a combination of movement of the hip + lower back. Ideally we want to move just the hip joint to get our leg in extension, sparing the spine the wear and tear of having to compensate for a lack of movement in the hip joint. In this drawing, the red dotted line shows that the two alignment points on the front of the pelvis remain vertical as the leg is moving behind the body. The red dot in the middle of the femur is the fulcrum around which the leg is moving within the hip joint. The spine remains unchanged.
But in what circumstances would we have to resort to a combination hip/spine movement – why does it occur and why aren’t we aware that we are doing it? It’s not like you would consciously choose to wear out your disks!
The amount of hip extension that a normal healthy hip should have varies depending on the source consulted but ranges from 5° to 30° (or more). The above picture shows extension of approximately 25°. Let’s simplify the pictures and look at a few more examples.
Picture A above shows a neutral pelvis (block) and a neutral femur. This would be like standing up with the leg vertical and the hip is in neither flexion nor extension. The lower back (lumbar spine) is also in a normal lordotic curve.
Picture B shows the hip in 25° extension with the block still in neutral. This is like the drawing above, where the hip is in extension and the spine is unaffected. So far so good.
Picture C shows the pelvis tilted. The femur is in 25° of extension relative to the ground but in fact, NO CHANGE has occurred in the hip joint itself. The movement occurred in the lower back. This is the unfortunate situation in the majority of people. We have lost our normal range of motion in the hip and have to resort to moving our pelvis and spine to get what looks like a normal gait pattern. In fact, with every step you take, you are creating damage to the disks of the lumbar spine.
In order to restore range of motion to the hip and prolong the life of the lumbar spine and disks, one must lengthen the hip flexors and stop sitting all day long. Getting the pelvis in alignment and restoring the natural reflex driven gait pattern that utilizes hip extension over hip flexion is also necessary. Restorative Exercise™ is a great choice for learning how to get your hips moving again.