Whether your post-run ritual involves jumping into the shower or meeting friends for a beer, it probably doesn’t often include stretching. Compared to running, holding your muscles in elongated positions can seem boring, and besides, there’s always next time.

But then a pull in your calf or pain in your hamstring sidelines you. If you’re like many of the runners I see as a physical therapist, you blame your injury on your lack of stretching. But is not stretching really at fault?

Overwhelmingly, the evidence points to overuse as the leading cause of running injuries. Overuse injuries can be viewed as a mismatch between what you’ve done and what you can handle.

That nagging sensation in a muscle may be because of weakness rather than tightness, which is best defined as muscle shortening. Weaker muscles often masquerade as tight muscles, owing to neurological changes within the muscle. If the muscle isn’t strong enough to do everything it needs to do, it can seize up to protect itself, leading to a feeling of tightness.

When this is the case, you’ve probably tried stretching for weeks, but haven’t noticed any long-term relief. These muscles typically measure normal in length. Instead of being too tight, they are too weak to handle the loads to which they’ve been subjected.

So, is your tight feeling truly muscle shortening, or is it weakness? And how do you distinguish between them? Let’s take a look at three muscle groups that often feel tight, and how to tell the difference between muscle shortness and weakness, as well as treatments for both.

Hamstrings

While running, your hamstrings are responsible for slowing the forward motion of your hip as you bring your leg forward and pushing your hip back after you hit the ground. The hamstrings are also the most commonly injured two-joint muscle in running. Many athletes who enter my clinic with a leg injury report hamstring tightness; when tested, however, these muscles are typically normal in length. The discomfort can instead be chalked up to weakness.

How do you know if your hamstrings are inflexible?

Lie on your back on the floor with both legs out straight. Bend the leg you’re testing so that your thigh is perpendicular to the ground. Next, try to straighten your knee. If your lower leg comes within 30 degrees of forming a straight line with your thigh, flexibility isn’t a problem.

Instead, you’re better off strengthening your hamstrings, such as with deadlifts or leg curls. Here are two moves you can do regularly to get your hamstrings stronger.

Deadlift With Flex Band

Hamstring Curl

If you fail the flexibility test, you can stretch your hamstrings by standing, putting the leg you’re stretching on a stool and leaning forward until you feel a stretch in your hamstrings. Hold this stretch for at least 60 seconds after your run.

Calves

The calf is one of the most important muscle groups in running, as the gastrocnemius and soleus propel you forward. Ankle mobility, especially the ability to adequately flex your foot when weight bearing, is crucial in running, and is often lacking after ankle sprains. Many people, however, report feelings of tightness in their calves even when their ankle mobility is adequate.

To test your calf flexibility, place the foot being tested four inches from a wall. Without lifting your heel or letting your lower leg or foot twist, lunge your knee towards the wall. Your knee should be able to easily reach it.

If so, strength may be the issue. A runner should be able to easily perform 25 calf raises on each leg, but even beyond this baseline, calf strengthening is important for all runners. One of the best ways to strengthen the calves may also help stretch them. To do this, perform a single leg heel raise off a step while letting your heel sink below the level of your toes.

If your flexibility is lacking, the calf can be stretched by facing the wall in a staggered stance, and leaning into the wall while keeping your back heel on the ground and without letting your foot cave in. This stretch can be done with the knee bent and straight. Maintain this stretch for at least three sets of 20 seconds or two sets of 30 seconds.

Hip Flexors

The hip flexor group is what drives your leg forward when it’s in the air. It’s yet another muscle group that often feels tight when it’s actually weak.

To test your hip flexor length, sit on the edge of a firm table, hug one leg into your chest, and let the leg you’re testing fall toward the table, as you lie back. Your thigh should hit the table.

Assuming you have adequate hip flexibility, you can strengthen your hip flexors by lying on the ground with a band around your feet, bending your knee, and pulling your leg into your chest against the resistance.

If your hip flexors are indeed short, perform the aptly named runner’s stretch by kneeling in a lunge without arching your back. Hold this stretch for at least 60 seconds.

If after taking these tests, flexibility and strength are both an issue, I recommend both stretching and strengthening, but focusing on strength training. While there is currently a lot of debate in the exercise science world about stretching, there is overwhelming evidence to support strength training as a means to reduce injury risk in runners.

Jasmine Marcus is a doctor of physical therapy, writer, and runner. Before becoming a physical therapist, she was a journalist. She works at an outpatient orthopedic clinic in upstate New York.

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