Here's Why Your Knee Hurts When You Bend It

And what to do about it.

Why does your knee hurt when you bend it? Docs explain.

Seeing as the knees are meant to bend, it can be a (literal) pain if they hurt when you do so. Whether it’s a dull throb or a sharp twinge, knee pain can make walking uncomfortable, and running or other forms of exercise pretty much impossible. Even sitting and sleeping can be difficult when your knees are giving you a hard time.

As it goes with any type of pain, there are lots of reasons why your knees might hurt when you bend them, including injuries to the ligaments and meniscal cartilage of the knee, says Dr. Grant K Radermacher, DC, a chiropractor and owner of Ascent Chiropractic. “But as much as ACL tears and meniscus injuries are talked about, unless you've been out playing high-impact sports and had a sudden onset of pain, it's unlikely they're the root of your problem.”

A much more common source of knee pain is a condition called patellofemoral pain syndrome, aka PFPS or runner’s knee. “Patellofemoral pain syndrome occurs in the front of the knee, under the kneecap, and is common in runners, cyclists, and basically anyone who sits for a living,” Radermacher says. “The pain usually starts out mild but often becomes progressively more intense and increasingly present if not properly addressed.”

Read on below for more on why your knee hurts when it bends and what you can do to remedy the situation.

Why Your Knee Hurts When You Bend It


While everything might feel fine when your leg is straight, knee pain can really stand out when you bend your legs to sit or squat — or even take a gentle step. Here’s why: Typically, your kneecap glides smoothly up and down in a groove created by V-shaped notches in your femur (aka the thigh bone), and the tibia (the large bone in your leg), Radermacher explains.

As the knee flexes and extends, the kneecap slides, rotates, and tilts. “This motion is what’s referred to as patellar tracking,” Radermacher says. “If the kneecap tracks incorrectly, usually due to misalignment of those V-shaped patellar grooves in the femur and tibia, it can cause damage and inflammation to the cartilage, bursa, and soft tissues beneath it.”

If your patella isn’t tracking correctly, Radermacher says walking, running, and other activities that cause repeated knee flexion, like cycling, will start to create inflammation, which in turn leads to that nagging pain. But exercise isn’t the only culprit. “Extended time spent sitting can contribute to PFPS because the structures supporting the kneecap can actually get fatigued by keeping your knee constantly flexed,” he adds, which is why it’s recommended to get up and move throughout the day.

Similar to PFPS is another type of overuse injury called tendonitis, which is the inflammation of the patellar tendon. It can crop up due to muscle imbalances in the leg, a sudden increase in physical activity — think running for the first time in ages — or if you have tight muscles. “Tightness or weakness in muscles or other tissues may be the reason for pain,” says Jazmin Morris, PT, DPT, OCS, a doctor of physical therapy with SportsMed Physical Therapy. Morris points to tight quads muscles in particular, which can pull on your knee joint and cause it to hurt when your knee is bent.

How To Stop Knee Pain

PhotoAlto/Odilon Dimier/PhotoAlto Agency RF Collections/Getty Images

If you have knee pain, rest and ice are the best first steps for reducing inflammation, Radermacher says. “After you've got the acute inflammation toned down, start with some gentle isometric quad contractions,” he adds. “They reduce pain through an effect known as descending analgesia.”

In general, it can take knee pain anywhere from four to six weeks to fully go away. “However, every body is unique,” Radermacher says. “Some may recover more quickly while others take longer to heal.”

To help the process along, Radermacher recommends adding a few exercises that are known to help knee pain, too. Runner’s knee, in particular, is often the result of weak pelvic stabilizing muscles, he says. Fortunately, that means you can fix it with some gentle strength training. For weak pelvic stabilizing muscles, focus on the muscles in your butt.

Ultimately, however, your best solution will depend on what caused your knee pain in the first place, Morris says. “If it was related to a change in activity, such as starting a new exercise program or increasing activity too quickly, it’s essential to make sure you properly warm up prior to exercise and progress slowly and thoughtfully in intensity, frequency, and/or difficulty,” she says. “If it’s related to muscular imbalances, making sure you continue with targeted exercises that address those issues can help prevent further problems.”

Three exercises that can help are the following:

Isometric Quad Contractions:

Lie on your back with a rolled towel positioned underneath the affected knee. Contract your quadriceps or thighs and try to press the towel into the floor with the back of your knee. Hold the contraction for five to 10 seconds then relax. Repeat 10 times.

Standing Side Leg Lifts:

Loop a resistance band just above your knees and stand with your feet about 10 inches apart. Shift your weight to your left foot and raise your right leg to the side as far as possible. Slowly return to the starting position. Repeat 10 times. Switch to the left leg and repeat.

Open Glute Bridge:

Loop a resistance band around your legs just above the knees. Lie on your back with your knees sharply bent and your feet flat on the floor about 10 inches apart. Lift your butt off the ground, push your hips forward, and pull your knees apart to stretch the band as far as you can. Hold this position for five seconds, then relax. Repeat 10 times.

When Should You See A Doctor?

If nothing changes when you ice your knee, warm up prior to exercise, or when you add a few gentle exercises for knee pain to your routine, then it may be time to see a doctor. “Left untreated, PFPS can become a chronic problem that can be just as debilitating as more serious [injuries],” Radermacher says. “It's generally a good idea to get patellofemoral problems under control as quickly as possible.”

When you stop by your doctor, they’ll consider the type of knee pain you have and what aggravates it to zero in on the cause, Morris says. Then they’ll prescribe a long-term treatment plan that addresses the structures that are weak, restricted, or malfunctioning. As Morris says, “This may include personalized exercise recommendations, manual therapy, and in some cases, use of tools such as braces or wraps.” In other words: whatever it takes to get you back in action.

Studies referenced:

Collins, N. (2016). Pain During Prolonged Sitting Is a Common Problem in Persons With Patellofemoral Pain. Journal of Orthopaedic & Sports Physical Therapy.

Goffaux, P. (2007). Descending analgesia — when the spine echoes what the brain expects. Pain. doi: 10.1016/j.pain.2006.11.011.

Mellinger, S. (2019). Evidence based treatment options for common knee injuries in runners. Ann Transl Med. doi: 10.21037/atm.2019.04.08.

Raj, MA. (2022). Knee Meniscal Tears. In: StatPearls [Internet]. Available from:

Rowe, J. (2007). Hip strength and knee pain in females. N Am J Sports Phys Ther. PMID: 21522212; PMCID: PMC2953297.


Dr. Grant K Radermacher, DC, chiropractor, owner of Ascent Chiropractic

Jazmin Morris, PT, DPT, OCS, physical therapist with SportsMed Physical Therapy.