Why Do My Knees Crack and Pop When I Squat?

During a round of squats, you probably expect to feel your glutes fire up and your quad muscles engage through the movement—but what you might not expect is to hear a sudden crunching, cracking, or popping noise from one or both of your knees. Though the sound itself can make you cringe, the good news is that as long as the popping itself isn’t painful, it’s usually nothing to be too worried about.

“Cracking knees while doing squats is extremely common,” says James Bicos, MD, a sports medicine orthopedic surgeon with Corewell Health in Bingham Farms, Michigan. In fact, he estimates that more than 50 percent of the patients he sees experience some form of knee cracking when squatting. 

But while usually harmless, there are still a few red flags to look out for when it comes to the health of your knees. Here’s everything you need to know about knees cracking when squatting—plus when to reach out to your doc.  

Why Do My Knees Crack When I Squat?

The official word for what’s happening here is “crepitus,” which refers to the snapping, popping, or cracking sound that can come from your knee when you move it in a certain way (and the deep bend that accompanies a squat is a common culprit). The sound occurs when the surface of a joint—in this case, the patellofemoral joint, which is where your kneecap connects with your femur—rubs against cartilage or other tissues. 

It’s sometimes a little unclear what causes crepitus, says Todd M. Melegari, MD, a sports medicine orthopedic surgeon at GBMC Healthcare in Towson, Maryland. But you could experience this crackling sound if you have one of the following:

1. Cartilage Loss 

Knee crepitus is often the result of age-related changes in cartilage. The knees are a major area for cartilage loss, in part because you use them so heavily over the course of your life. And without all that cushy cartilage padding the patellofemoral joint, your movements become less smooth and the surface of the joint can rub roughly—and loudly—together. “I compare it to tread on a tire,” Dr. Melegari says. “It’s generally nice and smooth, but as it wears, it can have rough spots—and as you bend your knees, the irregular surface can cause that popping.”

2. Inflammation

Sometimes swelling around your knee—which might be caused by overuse, an injury, or another health condition, as a few examples—can lead to crepitus. “If the lining of the joint thickens, it can get pinched as you bend your knee and give you that cracking sensation,” Dr. Melegari explains. You should always let your doctor know if you’re experiencing crepitus along with pain or swelling. 

3. Osteoarthritis

As we mentioned above, many people experience cartilage loss around certain joints as they age, leading to a cracking sound when the joint is bent deeply. But if the knee popping you’re hearing is also accompanied by pain and other uncomfortable symptoms, you might have osteoarthritis, a degenerative joint disease. Cartilage loss is a precursor to osteoarthritis, Dr. Melegari explains, and the pain, stiffness, and swelling you feel is “a direct result of cartilage wear and tear.” It’s important to get treatment if you think you have osteoarthritis in your knee or any other part of your body; treatment can help you feel better and prevent further damage to the joint.

4. Simply Bending the Joint In a Deep Way

Age or injury isn’t always to blame. “We also know that people in their 20s can have knees that crack,” Dr. Bicos says. Sometimes, this is just a function of the way you’re moving, he explains: When you squat down deeply, the lining of your knees can get in the way and lead to that cracking or crunching sound. 

It’s also possible that the movement of fluid around your kneecaps might play a role, Dr. Melegari says. “The knees have a trace amount of fluid around them, which can get trapped then released,” producing a popping sound, he says. You might experience this even if your cartilage is otherwise in excellent condition.

Can You Prevent Your Knees from Cracking and Popping During Squats?

If your knees crack when you squat but you aren’t experiencing any pain, “we don’t recommend doing too much about it,” Dr. Bicos says. (Pain or swelling when your knees crackle is another story, though—more on what to do if this happens to you below.) 

Still, it’s critical to stretch before and after all forms of exercise, regardless of whether you’ve been having crepitus. Before starting a workout with squats, Dr. Bicos recommends focusing in particular on the muscles that support your knee, including the hamstrings and quadriceps. Strengthening these same muscles—such as with weight-training exercises, indoor cycling, or swimming—can also help prevent future problems with your knees.

Crepitus isn’t necessarily the result of improper squat form, Dr. Melegari says, but it’s also important to make sure you’re doing them correctly to reduce risk of injury: Always make sure your back is straight, your knees track over your toes (not beyond them!), your weight is evenly distributed, and your core muscles are engaged.

And if knee cracking really bothers you, even if you’re not experiencing pain? Sometimes limiting your range of movement can help minimize that sound. “If you’re squatting down to 90 degrees, maybe make it to 45 degrees,” Dr. Bicos says. “Or, if you’re going to be doing big lunges, modify them a bit so you’re not going as deep as you were before.”

What If My Knees Pop During Other Forms of Exercise?

That cracking, popping sound is very common during squats, but you’re likely to hear it during other types of movement too. “Anything that involves bending the knee can produce it,” Dr. Melegari says. That might include standing up from a seated position, getting in and out of a car, going up and down steps, or doing lunges, as a few examples. 

That said, it’s also not impossible to experience crepitus when you’re extending your leg, like when walking or running. The exact cause can sometimes be unclear, but as long as it’s not causing you pain or any other uncomfortable symptoms, “generally that popping, crunching sound is almost always harmless,” Dr. Melegari says.

When to Talk with Your Doctor About Cracking or Popping Noises in Your Knee

Knee crepitus on its own is usually no big deal, and many people experience cracking from time to time when moving deeply into a squat position. But you should let your doctor know if you notice any of the following red flags when your knees crackle:

Symptoms like these could suggest that the knee cracking you’re hearing is also a sign of something more serious, such as osteoarthritis or a knee cartilage injury. Having your doctor evaluate your knee promptly is important in these situations. If osteoarthritis is untreated, for example, it can lead to further joint damage.

The Takeaway

It’s usually pretty normal if your knees crack when you squat. Natural changes in cartilage as you age, generalized inflammation, or simply deeply bending your knee can cause the cartilage and soft tissues surrounding the joint to rub together roughly. This, in turn, can produce a cracking or popping sound, officially called crepitus. Most of the time, knee crepitus isn’t something you have to be too concerned about. “If it’s not interfering with your quality of life and it doesn’t slow you down or make you think twice about an activity, you probably don't have to worry,” Dr. Melegari says. But if knee popping is accompanied by pain, swelling, stiffness, a locking sensation, or if it feels like pebbles grinding together, reach out to your doctor.