Why Does My Knee Hurt When I Run? Common Causes and What to Do About It

Knee pain can turn a good run into a frustrating one quickly. It can also be confusing. Your knee may hurt even though nothing obvious happened to injure it.

For runners, knee pain often develops from a combination of factors rather than one specific event. Changes in training, strength, mobility, recovery, and running mechanics can all affect how much stress your knee handles with every stride.

The location of your pain can provide useful clues about what may be causing it.

Where Does Your Knee Hurt When You Run?

Pain in the Front of the Knee

Pain around or behind the kneecap is commonly associated with patellofemoral pain, often called runner's knee.

You may notice pain while running, going down stairs, squatting, or after sitting with your knee bent for a long time.

Runner's knee does not necessarily mean there is something structurally wrong with your kneecap. Training load, hip and leg strength, mobility, and the way forces move through your leg while running can all contribute.

This commonly happens when runners ramp up training too quickly, or when seasoned runners run too much — doing one marathon after another. They think that by doing more squats and lunges at the gym they will strengthen it. Actually, we need to look at biomechanics. Glute and core strength could be affecting it. The instability causes excessive tightness in the quads and IT band, which then causes the pain and tension at the patella.

Pain on the Outside of the Knee

Pain along the outside of the knee is often associated with irritation involving the iliotibial band, commonly called IT band syndrome.

Runners may initially notice the pain several miles into a run. As it becomes more irritated, the pain may begin earlier or linger afterward.

Changes in mileage, hills, terrain, strength, and running mechanics can contribute.

Many think you can stretch the IT band. You can't. Usually it is the adherence of the IT band to the outer part of the quad (vastus lateralis) that is tight. We need to make this overlapping part more mobile. An IT band stretch really doesn't work.

Pain Below the Kneecap

Pain just below the kneecap may involve the patellar tendon. This tendon connects the kneecap to the shinbone and handles substantial force during running and other athletic activities.

Symptoms can develop when the tendon is exposed to more load than it is currently prepared to tolerate.

In runners, patellar tendon pain often follows a jump in speed work, hill training, racing, or overall mileage. An overstriding pattern, reduced hip or calf contribution, and limited strength or endurance in the quadriceps can also concentrate more load at the tendon. Tendons usually respond best to a gradual, progressive loading plan rather than complete rest or an abrupt return to full training.

Pain on the Inside of the Knee

Pain along the inside of the knee has several possible causes. The location alone is not enough to determine what is happening.

If pain persists, particularly if it is accompanied by swelling, locking, catching, or instability, an evaluation may be appropriate.

Running-related possibilities include irritation of the pes anserine tendons or bursa, overload of the medial joint line, or stress related to the way the hip, knee, and foot move together. A recent increase in hills, speed, mileage, or uneven terrain may provide an important clue. Because several structures can produce similar symptoms, the timing of the pain, tenderness, swelling, and movement findings matter more than the location alone.

Why Does Knee Pain Develop in Runners?

Finding the name for a painful condition is only part of the problem.

The more useful question is often: Why did this start happening now?

A Change in Training Load

A sudden increase in mileage, speed work, hills, racing, or training frequency can expose your body to more stress than it has adapted to handle.

That does not necessarily mean you are running "too much." It may mean the change happened too quickly for your current capacity.

For example, a runner may feel comfortable at 15 miles per week, then begin race preparation by increasing to 25 miles while adding a weekly hill workout. Each change may seem reasonable on its own, but together they create a much larger jump in stress. Temporarily reducing one variable and rebuilding it gradually can allow the knee to adapt without abandoning the runner's goal.

Strength and Capacity

Running places repeated demands on your hips, knees, calves, ankles, and feet.

If certain muscles are not strong enough to manage those forces over thousands of strides, other tissues may absorb more stress.

Strength training can therefore be an important part of both recovering from and preventing running injuries.

The most common deficits we find are reduced strength or endurance in the gluteal muscles, quadriceps, calves, and trunk. We also look for side-to-side differences and for a runner's ability to control the hip, pelvis, and knee during single-leg tasks. A runner may be strong in a traditional two-legged gym exercise but lose control after repeated single-leg loading, which is more similar to the demands of running.

Mobility

Running does not require extreme flexibility, but your body needs enough movement in the right places.

Restrictions at the hip, ankle, or elsewhere can change how your leg moves and how forces are distributed during running.

We commonly see limited ankle dorsiflexion, reduced hip extension, and stiffness in the calves, quadriceps, or hip flexors. These restrictions can change where the body absorbs force or lead to compensations at the knee. We focus on the limitations that actually affect the runner's movement rather than trying to make every joint as flexible as possible.

Running Mechanics

Two runners can cover the same distance at the same pace while placing very different demands on their bodies.

Cadence, stride length, foot placement, hip and knee position, and other elements of running mechanics can affect how forces move through the body.

This is one reason simply identifying "runner's knee" may not solve the problem. The diagnosis describes where you hurt. It does not necessarily explain why you hurt.

At Peak, a running analysis combines a comprehensive physical therapy examination with slow-motion video and 3D motion-capture data. We assess posture, strength, range of motion, single-leg control, cadence, stride length, foot placement, and hip, pelvis, and knee positions while the runner moves at a representative pace. Noraxon myoMOTION sensors quantify joint angles, and video from multiple views helps us connect those measurements to what the runner is actually doing. We compare the running findings with the physical exam and symptom pattern, and consider how these findings may influence the runner's pain or performance issues. The runner then receives an individualized explanation, report, and exercise plan rather than a one-size-fits-all recommendation to change form.

What Should You Do About Knee Pain From Running?

The answer depends on what is causing the pain.

Simply stopping running until the pain disappears may calm the symptoms, but it does not necessarily address the reason they developed.

An effective plan may include:

• Temporarily modifying mileage or intensity
• Building strength and tissue capacity
• Improving relevant mobility
• Adjusting recovery or training progression
• Changing specific aspects of running mechanics when appropriate
• Gradually rebuilding running volume

The goal is not simply to make your knee stop hurting. It is to help your body tolerate the running you want to do.

We start with the runner's goals, symptom behavior, training history, physical exam, and running analysis. If the main trigger is a sudden training spike, load modification may be the priority; if testing reveals strength or mobility deficits, we build those capacities progressively. We recommend a mechanics change only when it is connected to the runner's symptoms and can reduce relevant stress without creating a new problem elsewhere. Most runners need a combination, with the plan adjusted according to how the knee responds during the run and over the following day.

Can You Keep Running With Knee Pain?

Sometimes. Knee pain does not automatically mean you need to stop running completely.

The answer depends on the severity of your symptoms, how they respond during and after running, and what is causing them.

As a general guide, mild discomfort (about 0-3 out of 10 level) may be acceptable if it stays stable rather than building during the run, does not change your gait, and returns to your usual baseline by the next morning. If pain steadily increases, becomes sharp, causes limping, or remains notably worse the following day, reduce the distance or intensity and have the problem assessed. Do not run through substantial swelling, locking, repeated giving way, an inability to bear weight, or pain following a significant traumatic injury. These guidelines are not a diagnosis. The appropriate limit depends on the tissue involved and the individual runner.

When Should You Get Your Knee Checked?

Consider getting evaluated if your knee pain persists, repeatedly returns when you run, gets progressively worse, or is preventing you from training normally.

More immediate evaluation may be appropriate following a significant injury or when symptoms include substantial swelling, inability to bear weight, locking, significant instability, or other concerning symptoms.

Seek prompt medical care for obvious deformity, rapidly developing swelling after an injury, a hot or markedly red joint, fever or unexplained illness with knee pain, severe calf swelling or tenderness, new numbness or weakness, or an inability to fully straighten the knee after it locks.

Find the Cause, Not Just the Pain

If your knee hurts every time you run, the answer may not be simply to rest longer.

The question is why your knee is receiving more stress than it can currently handle.

For one runner, the answer might be training progression. For another, it could be strength or mobility. For another, running mechanics may play an important role. Often, several factors contribute at the same time.

At Peak Physical Therapy in Cupertino, we work with runners to identify those factors and develop a plan designed around getting them back to the running they want to do.

One runner came to Peak after developing pain in both knees following a first marathon and was unable to run. The runner initially sought help from other providers, but Peak's evaluation identified insufficient gluteal support as an important contributor. After following a targeted strengthening program, the runner returned to running and began training for a second marathon.

Ready to understand what is driving your knee pain? Request a running analysis or physical therapy evaluation at Peak Physical Therapy, or call or text the Cupertino clinic at (408) 366-1735. Learn more about our running analysis.