Healthy hip flexor muscles are essential for runners—not only do you need them strong, but mobile too. Just think about your stride: When you push off the ground, your hip flexor muscles drive you forward, providing speed, power, and quick turnover. And while your hamstrings and glutes are responsible for most of the force at push-off, your hip flexors dictate how far behind your body your leg can go and how far you can drive your knee up. A shortened range of motion at the hips (thanks to tight hip flexors), means you slow down and risk injury.
“[Tight hip flexors are] going to limit the amount of force and propulsive motion that you can use to go forward,” says Kristopher Ferrera, doctor of physical therapy at Moss Rehab, where he specializes in running injuries. The hip flexors also connect to the low back, so if they’re tight, they’ll compromise spinal positioning, which affects posture. Bad posture decreases efficiency and also increases injury risk.
Luckily, there’s a simple movement test to determine whether or not you suffer from tight hip flexors. It’s called the Thomas Test.
What is the Thomas Test?
Named after the British orthopedic surgeon Hugh Owen Thomas, the Thomas Test is a physical examination used to determine if patients suffer from psoas syndrome or hip flexion contractures (the former refers to overuse of the hip flexors and the latter is a permanent shortening of them). The test caught on because of its simplicity, and now, it’s often used to assess muscle tightness.
“It’s easy to reproduce between clinicians and patients,” says Ferrara. “It gives you some good information that can indirectly affect not only athletic performance, but also can help tell you what's going on if you're having pain in different areas.”
The Thomas Test examines the iliopsoas, the group of muscles that connects the spine to your legs, through the pelvis; the rectus femoris, the quad muscles that run from your hip to your knee; and the tensor fascia latae, the lateral thigh muscle that lies underneath your iliotibial band. Collectively, they make up the hip flexor muscles. Depending on the results of the test, you’ll know which of them needs treatment.
How to perform the Thomas Test
Ferrara describes the easiest way to perform the Thomas Test: Lie faceup on the very edge of your bed or a sturdy table, so your legs hang off. Bring both knees towards your chest so your back lies flat against the bed. While holding one knee close to your chest, slowly straighten your other leg and let it hang off the edge.
You passed the test if your back and the back of your lowered thigh is flat against the bed, and your hanging knee is bent at a 90-degree angle off the surface.
There are a few things to look for when it comes to failing the test.
If your lowered leg extends out straight instead of bending at the knee, your rectus femoris is tight. If your lowered knee is bent, but the back of your thigh is elevated off the bed, then it’s your iliopsoas.
If your lowered leg is bent at the knee and your thigh is resting on the bed, but your leg hangs slightly out to the side, then your tensor fascia latae is tight.
According to Ferrara, distance runners will most likely experience the second outcome—a tight iliopsoas.
How to treat for a failed Thomas Test
“One of the nice things about this is the test can turn into the treatment,” says Ferrara.
The Thomas Stretch is well-known: Pull one knee into your chest while lying faceup on an elevated surface, which you’re already doing as you test. Just make sure to maintain a flat back and thigh and keep your lowered knee bent at a 90-degree angle. Hold that stretch for 30 seconds to a minute.
Ferrara also recommends the lunge stretch: Get into a kneeling lunge position, with one foot forward. Lean forward as you squeeze your glutes, engage your core, and straighten your spine. Hold the stretch for 30 seconds to a minute.
Finally, Ferrara says that because the hip flexors are so deeply embedded under layers of muscle, using a lacrosse ball to roll the area out will work wonders. If a lacrosse ball is too intense, you can start with a tennis ball or softball.
As for how long before you start to see results, Ferrara says to be patient: “Muscles take a little bit of time to remodel with stretching. So it's generally five to seven days a week of three minutes total per day.” With just static stretching, it can take eight to 10 weeks, so he recommends adding in lacrosse ball work to speed up the process.