Maybe they’re tight, maybe you’ve got a pull or strain, maybe they get really sore. Or maybe they don’t bother you at all but you’ve been told they’re the source of another problem such as back pain or plantar fasciitis. Whatever’s got you looking to solve a hip flexor problem, there’s something important you need to know.
The main muscles that flex your hip joints are your iliopsoas, rectus femoris, sartorius, and tensor fasciae latae. In the context of running we think of their job as bringing the knee forward and up, which means we think of them working in the sagittal plane (the front-to-back plane of motion). In this view, hip flexion happens when your thigh comes up directly in front of your hip joint and hip extension—the official anatomical term is actually hip hyperextension—happens when your thigh moves directly behind your hip joint.
This results in people doing stretches like this for the hip flexors:
But there’s a problem with this view, and it’s a problem that will keep your hip flexors an issue even after you’ve done a lot of work on them.
The problem is that most of the hip flexor muscles don’t work exclusively in the sagittal plane. And what’s more, hip flexion and extension in running are not exclusively sagittal plane activities.
Take the iliopsoas, the most powerful group of hip flexors. As you can see, they run from the inside of the lumbar spine and pelvis to the inner thighs. So if you hold your spine and pelvis perfectly still, they will flex your hips. They will also, in a fairly simple way, flex your hips if you contract both sides at once.
But in running your pelvis and spine don’t stay perfectly still. Also, you only contract one side at a time since your legs are moving opposite each other. When you contract just one side of the iliopsoas, you not only flex the hip joint, you also lift that side of your pelvis. And at the same time, as the other leg moves underneath and behind you, the iliopsoas lengthens, allowing that side of the hip joint to tilt downwards and the leg to move behind the pelvis.
A full contraction of the iliopsoas on one side moves your pelvis and spine as well as your leg. A full lengthening of it does the same in the other direction.
So thinking of your hip joints as hinges and doing exercise and movement based on that image doesn’t match either the anatomical reality or the movements you do when you run, and you’ll have limited success and a lot of extra stress from any exercises you do that work on that model.
When you move your legs in running your pelvis is also moving, and the structure of your hip flexors are part of this system.
This means that as a runner’s leg passes behind them and their hip joint extends, that side of their pelvis moves down and backwards.
And as a runner’s leg comes in front of them and their hip joint flexes, that side of their pelvis moves up and forwards.
For an image of how this works, check out this video I made of myself in a gait lab a year and a half ago.
If you think of hip extension as happening just in your hip joint and try to, for example, push that side of your pelvis forwards as the thigh passes backwards in order to maximize the movement in your hip joint specifically, you’re actually interfering with your hip extension by making your pelvis move the opposite direction that it should. Your ilipsoas on that side can’t properly lengthen, and that reduces how far back your leg can go.
And ditto if you try to maximize your hip flexion by pulling that side of your pelvis backwards as your knee moves forwards and up. You are preventing your hip flexors from properly shortening (and this is a perfect recipe for hamstring problems, by the way).
This goes for the action of running and also for exercises or stretches you do for your hip flexors. It’s popular in fitness right now to take a super-mechanical isolated view of actions and muscles. So people consider any movement of the pelvis in hip flexor stretches or strengthening to be “cheating.”
It isn’t. It’s just your body trying to work right.
It really is possible that your hip flexors are chronically held a bit too short for the comfortable, fast running you’d like to do. In fact, as a modern human who likely sits too much, it’s probable that your hip flexors are habitually too shortened even for really good walking and standing.
The cure for this is to do a lot of hip-extending activities that include the movement of your pelvis in the action of your legs. The movement of your pelvis won’t be massive, but it’s important.
When you do movements or exercises that involve hip extension (or hyperextension if you prefer), let that side of your pelvis shift appropriately slightly down and back.
And when you bring your leg in front of you, let that side of your pelvis shift up and forward slightly to facilitate it.
The harm that so much sitting does to the hip joints isn’t only that the actual femurs rest in the hip sockets in flexion for untold hours each day, but also that the pelvis is held level and square. We’re now aware of the hip joint part of this is a problem, but the level, static, passive pelvis has not yet been recognized for the companion problem it is…and too often is put forward as the solution instead!
After all the most stable pelvis of all is the one that’s in the seat of a chair.
When you move your pelvis moves. When your hip joints go through a range of motion, so does your pelvis. And when you allow this to happen, the reduction in tension you’ll feel around your hips will help your running in the way you’ve been seeking.
Sign up for our free weekly newsletter filled with analysis, information, insights, and tips you can apply to your own running!
Jae Gruenke, GCFP, is a running technique expert and Feldenkrais Practitioner. Known as a “running form guru,” she is the Founder and CEO of The Balanced Runner™ in New York City and The Balanced Runner UK. She has helped runners from beginner to Olympian improve their form to become pain-free, economical, and fast.