The Biggest Lie in Fitness

Despite what the internet or rehab professionals tell you, your hip flexors are not tight and anterior pelvic tilt (APT) is not causing your back/hip pain. The purpose of this article is to discuss the misunderstood relationship between anterior pelvic tilt and tight hip flexors.

Here are a couple thoughts that come to mind:

  1. Just because you have an APT does not mean you have “tight hip flexors.”

  2. Hip flexors implicates a group of muscles, not just one muscle. This matters when assessing posture and function.

  3. You can have an APT and still be in hip extension.

  4. The most discussed hip flexor, the iliopsoas, is typically long and/or weak not tight.

  5. The hips typically prefer flexion not extension.

The first thing clinicians and trainers need to realize when looking at standing posture is that hip position is dependent on the knee joint angle AND by the pelvic tilt. Thus, someone can have an anterior pelvic tilt and still be in hip extension if the knees are in extension. In hip extension, the hip flexors can be in a lengthened position; you can also have a posterior pelvic tilt and be in hip flexion. This is a very important distinction.

To start we have multiple hip flexors:

1. Iliopsoas – Attaches at the lumbar spine and hip. We can see by the line of pull the iliopsoas flexes the hip, laterally rotates the hip (turns your knee outward), and provides stability to the anterior joint structures of the hip (helps prevent the head of the femur from gliding out the front of the hip socket). The iliopsoas also acts on the pelvis to tilt the pelvis anteriorly.

Iliacus and psoas major combined to form iliopsoas

2. Tensor Fascia Late (TFL) – Attaches at the pelvis and knee via the iliotibial band (ITB). One important thing to realize is the TFL has no direct attachment to the femur unlike the iliopsoas. Its actions include flexion, medial rotation (turns the femur inward), and abduction of the hip. The TFL can also tilt the pelvis anteriorly and provide stability to the lateral structures of the knee via the iliotibial band.

3. Rectus Femoris – Attaches at the pelvis and the knee via the patellar tendon. Again, it is important to realize there is no direct attachment to the femur. Its actions include hip flexion and knee extension. The rectus femoris can also act to tilt the pelvis anteriorly.

So basically, what we have is different muscles that have synergistic and antagonistic actions. For example, take a look at the client below (disregard my shoddy cover up work).

This client stood in significant hip extension with a mild APT. Unfortunately, I did not capture this. However, we can pick out some important things from the front. Her right femur is medially rotated (turned in) and the tibia is laterally rotated (turned out) relative to the femur. Otherwise her foot would be turned in along with the femur.

Without going on too much of a tangent, people tend to forget that muscles function in multiple planes of motion and that despite muscles having similar actions they can also oppose each other. Remember, the TLF turns the femur inward while the iliopsoas turns the femur outward. In this client, the TFL was the dominant hip flexor while the iliopsoas was long and weak. So back to the original point, it’s usually not as black and white as: anterior pelvic tilt = hip flexion = tight hip flexors = stretch the crap out of them. If we are going to stretch the hip flexors it needs to be specific in regards to which hip flexors and how we want to stretch them.

The funny thing about people who usually stretch their hip flexors is that they do it a lot, often making things worse. There’s a reason for this.

They are stretching a hip that is already in extension into more extension. When this occurs not only are you stretching an iliopsoas that’s already long/weak but you are also leveraging the head of the femur into the front of the hip. It’s no coincidence that the most common site of hip pain is the front of the hip.

(As the knee goes backwards the head of the femur has to come forward. The line of force is represented by the red arrow.)

Here’s an excerpt from a research article discussing the hip and labral tears “ ….The third and most likely reason for the prevalence of anterior labral tears is that this region is subjected to higher forces or greater stresses than other regions of the labrum. Because of the anterior orientation of both the acetabulum and the femoral head, the femoral head has the least bony constraint anteriorly and relies instead on the labrum, joint capsule, and ligaments for stability. Despite its decreased stability, this area undergoes significant forces during daily activities.” (1)

In simpler terms, there is less stability in the front of the hip thus the body must rely on other structures such as muscular tension (even though it’s not directly stated) or cartilage/ligamentous/capsular support. As we mentioned before, the iliopsoas, due to its close proximity to the front of the hip joint, provides stability to this area.

Here’s what we typically see happen:

Person thinks they are in an anterior pelvic tilt so they decide to stretch their hip flexors. Unknowingly their hip flexor (iliopsoas) is already long, their hip is in extension, and they start cranking away at the front of their hip. Surprisingly they feel relief for a bit, however the stiffness/pain returns. So they repeat the process thinking more is better.

What is actually happening:

The body, which is regulated by the nervous system, prefers stability. If we are constantly fighting this stability by cranking on the front of our hip, things start to get pissed off. To prevent instability the nervous system creates stability. One way the nervous system does this is by creating stiffness in the muscles that surround a joint, i.e., the iliopsoas. Remember the TFL and rectus femoris have no direct control over the femur.

The pattern looks more like this:

Hip flexor to stretch the hip flexors > anterior hip irritation created by unnecessary stretching into hip extension > the nervous system creates stiffness to protect the joint > the hip starts to feel "tight" again > the person stretches to reduce protective stiffness > hip gets more irritated > protective stiffness returns > cycle repeats. How do we break the cycle, you got it, load the iliopsoas.

Sometimes it is as simple as strengthen what is long/weak and stretch what is short/stiff. The hard part is getting it right.

References 1. Groh MM, Herrera J. A comprehensive review of hip labral tears. Current Reviews in Musculoskeletal Medicine. 2009;2(2):105-117. doi:10.1007/s12178-009-9052-9.


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