Learn more about why you should care about this tiny muscle in your booty. Warning: You'll never skip pigeon pose in yoga again.
Photo: CheshiireCat/Getty Images

It's officially marathon season and that means runners are pounding more pavement than ever. If you're a regular, you've likely heard of (and/or suffered from) a slew of the usual running-related injuries—plantar fasciitis, iliotibial band (IT band) syndrome, or the all-too-common runner's knee. But there's another, quite literal pain-in-the-butt issue called piriformis syndrome that could be lurking in your glutes—and it can plague you whether you're a runner or not.

If you've got outer glute or lower back pain, there's a chance you have a pissed-off piriformis. Get the scoop on what it means, why you might have it, and how you can get back to crushing your fitness goals, pain-free.

WTF is a piriformis?

Most people think of their butt as just the gluteus maximus—but while that's the largest glute muscle, it's certainly not the only one. One of them is the piriformis, a small muscle deep in your glute that connects the front of your sacrum (a bone near the bottom of your spine, just above the tailbone) to the outside of the top of your femur (thigh bone), according to Clifford Stark, D.O., medical director at Sports Medicine at Chelsea in New York City. It's one of six muscles responsible for rotating and stabilizing your hip, adds Jeff Yellin, physical therapist and regional clinical director at Professional Physical Therapy.

What is piriformis syndrome?

The piriformis muscle lies deep inside your butt and, for the vast majority of people, it runs directly on top of the sciatic nerve (the longest and largest nerve in the human body, which extends from the base of your spine down your legs to your toes), says Yellin. Muscle spasms, tightening, loss of mobility, or swelling of the piriformis can compress or irritate the sciatic nerve, sending pain, tingling, or numbness through your butt, and sometimes in the back and down your leg. You'll feel the sensations whenever the muscle is contracted—in extreme cases, just from standing and walking—or during running or exercises like lunges, stairs, squats, etc.

What causes piriformis syndrome?

The bad news: Your anatomy might be to blame. Not everyone's sciatic nerve chills under the piriformis—there are anatomical variations in exactly where the nerve runs through the area that can predispose you to piriformis syndrome, says Dr. Stark. In as much as 22 percent of people, the sciatic nerve doesn't just run underneath the piriformis, but pierces through the muscle, splits the piriformis, or both, which makes them more likely to develop piriformis syndrome, according to a 2008 review published in the Journal of the American Osteopathic Association. And the cherry on top: Piriformis syndrome is also more common in women than in men.

Anatomy aside, any piriformis muscle issues can irritate that sciatic nerve: "It could be overtraining, where you're just overusing the muscle and it gets stiff and doesn't have that ability to glide, slide, and stretch the way it needs to, which compresses the nerve," says Yellin. It could also be muscular imbalances within the hip. "With so many small stabilizer muscles within the hip and lower back area, if one is being overworked and another is being underworked and you continue to develop those faulty patterns, that can create symptoms as well," he says.

The condition is particularly common in runners, because of the biomechanics at play: "Every time you take a stride forward and land on one leg, that front leg wants to internally rotate and collapse down and inward because of the sheer force and impact," says Yellin. "In this case, the piriformis acts as a dynamic stabilizer, externally rotating the hip and preventing that leg from collapsing down and in." When this motion is repeated over and over again, the piriformis can get irritated.

But runners aren't the only ones at risk: A whole slew of things—sitting for a prolonged period of time, going up and down stairs, and lower body exercises—can cause issues in the piriformis.

How is piriformis syndrome diagnosed?

Unfortunately, because these same symptoms can be red flags for other issues (such as a herniated or bulging disc in the lower spine), piriformis syndrome can be tough to diagnose, says Dr. Stark.

"Even diagnostic imaging tests such as MRIs can be misleading, as they often reveal disc disease which itself may not be causing the symptoms, and occasionally a combination of factors are causing the problem," he says.

If you think your piriformis is acting up, your best bet is definitely to have it seen by a doctor, says Yellin. You don't want to start guessing and self-diagnosing because of the possibility that it's one of these other more serious problems like a disc injury or pinched nerve in your spine.

How is piriformis syndrome treated and prevented?

Luckily, there are some simple things you can do to prevent and ease (albeit not cure) piriformis syndrome:

  1. Stretch, stretch, stretch: You guys—stop skipping your post-run stretch. It's one of the five things all physical therapists desperately want runners to do to avoid injury. Your two best bets for stretching out that piriformis? Figure four stretch and pigeon pose, says Yellin. Do three to five repetitions, holding for 30 seconds each. (While you're at it, add these 11 yoga poses perfect for runners to your routine.)
  2. Soft tissue work: "Imagine getting a knot in your shoelace," says Yellin. "What happens when you pull the string? It gets tighter. Sometimes just stretching isn't enough, and you have to actually target specific spots." The fix? Try self-myofascial release (with a foam roller or a lacrosse ball) or a see a massage therapist for active release. (Just don't foam roll your IT band.)
  3. Address your muscle imbalances. Many weekend warriors (people with desk jobs who are active outside the office) have tight hip flexors from sitting all day, says Yellin, which can mean they also have weak glutes as a result. You can pinpoint this and other muscle imbalances by seeing a physical therapist. (You can DIY it a little at home with these five steps to nix muscle imbalances, but a professional can give you the full workup.)

Just remember that these aren't a permanent solution: "It's just like anything with strength and flexibility: You put all that work in to make the gains," says Yellin. If you stop doing the stretches or strengthening exercises that helped eliminate your piriformis syndrome, there's a high likelihood of it returning, he says.