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

Knee pain is one of the most common problems runners deal with. It can show up suddenly during a run, gradually build over several weeks, or only bother you after you finish.

The frustrating part is that “knee pain” isn't one specific injury.

Where you feel the pain, when it occurs, how your training has changed, and how your body handles the demands of running can all help determine what's actually causing it.

If your knee hurts when you run, here are some of the most common reasons why.

1. Patellofemoral Pain (Runner's Knee)

Pain around or behind the kneecap is commonly referred to as runner's knee. The medical term is patellofemoral pain.

You may notice pain:

• Around or behind your kneecap

• During or after running

• Going up or down stairs

• Squatting

• After sitting with your knee bent for a long time

Despite the name, runner's knee doesn't necessarily mean there is damage to your knee.

Often, the knee has become irritated because the amount of stress being placed on it has exceeded what it can currently tolerate.

That can happen after increasing mileage, adding hills or speed work, returning to running after time off, or simply accumulating more training than your body has adapted to.

Strength, running mechanics, and recovery can also influence how much stress reaches the knee.

2. IT Band–Related Knee Pain

Pain on the outside of the knee during running may be related to the iliotibial band, commonly called the IT band.

This type of pain often starts after you've been running for a certain amount of time and may progressively worsen as you continue.

A common mistake is assuming that an irritated IT band simply needs to be stretched.

Instead, we want to know why that area is being overloaded in the first place.

Changes in training volume, hip strength, running mechanics, terrain, and how your body is absorbing force can all contribute.

3. Patellar Tendon Pain

If your pain is concentrated just below the kneecap, the patellar tendon may be involved.

Tendons generally respond well to load, but problems can develop when the amount of load increases faster than the tendon can adapt.

This can occur after introducing more:

• Speed work

• Hills

• Plyometrics

• Strength training

• Overall running volume

Complete rest isn't always the long-term answer for tendon problems. The goal is often to find an appropriate level of activity while progressively rebuilding the tendon’s ability to tolerate load.

4. Training Errors and Sudden Changes in Running

Sometimes the biggest clue isn't where your knee hurts.

It's what changed before it started hurting.

Think back over the few weeks before your symptoms began.

Did you suddenly increase your mileage? Start running more days per week? Add speed workouts? Start training for a race? Run significantly more hills? Return after taking time off?

Your cardiovascular fitness can sometimes improve faster than your muscles, tendons, bones, and joints adapt.

You may feel capable of running farther or faster even though your body isn't prepared for the increased workload yet.

5. Strength Deficits

Running requires your body to repeatedly absorb and produce force, often thousands of times during a single run.

Weakness doesn't automatically cause knee pain, but inadequate strength can reduce your ability to tolerate those repeated demands.

For runners with knee pain, I commonly assess strength throughout the entire leg rather than looking only at the knee.

That can include the:

• Hips

• Quadriceps

• Hamstrings

• Calves

• Feet and ankles

The important question isn't simply “Are you weak?”

It's whether you have enough strength and capacity for the amount and type of running you're asking your body to perform.

6. Running Mechanics

Running form can influence where forces are distributed throughout your body.

Things like cadence, stride characteristics, trunk position, and how you absorb force may contribute to the amount of stress placed on the knee.

But there isn't one perfect way everyone should run.

That's why I don't recommend randomly changing your running form just because you've seen a video telling you that you need to increase your cadence or change your foot strike.

A running assessment should look at your mechanics, your symptoms, your strength, and your training history together.

Should You Stop Running If Your Knee Hurts?

Not necessarily.

One of the biggest misconceptions about running injuries is that pain automatically means you need to completely stop running.

Sometimes temporarily reducing or stopping running is appropriate. Other times, you can continue running while modifying your mileage, speed, terrain, or frequency.

The right decision depends on the injury and how your symptoms respond.

Pain that is progressively worsening, significantly changing the way you run, occurring during normal daily activities, or failing to improve deserves further evaluation.

Sudden severe pain, substantial swelling, inability to bear weight, significant instability, or pain following a traumatic injury should also be evaluated rather than simply trying to run through it.

Why Rest Alone Doesn't Always Solve the Problem

Rest can make an irritated knee feel better because you're temporarily removing the activity that aggravates it.

But feeling better after resting doesn't necessarily mean you've addressed why the problem developed.

This is why some runners get stuck in a frustrating cycle:

Run → knee hurts → rest → knee feels better → start running again → knee hurts again.

If nothing changed between attempts, the same problem may return.

The goal shouldn't just be getting your knee to stop hurting.

The goal should be getting your knee and the rest of your body prepared to tolerate running again.

What I Look at When a Runner Has Knee Pain

When I evaluate a runner with knee pain, I'm not just looking at the knee.

I want to understand the entire picture.

That includes your symptoms, training history, strength, mobility, running mechanics, previous injuries, current training goals, and what changed around the time your pain started.

From there, we can determine what is most likely contributing to the problem and develop a plan for getting you back to running.

Knee Pain While Running in Denver?

If knee pain is keeping you from running the way you want to, Stride Running PT provides one-on-one physical therapy specifically for runners in the Denver area.

Instead of treating the painful area in isolation, we'll determine what's limiting your ability to run and build a plan around getting you back to your goals.

And because Stride Running PT is mobile, I come to you.

Ready to get back to running? Schedule your Physical Therapy Evaluation.