Why do knees hurt while running?

Every spring many people start the running season and eagerly go to the running paths. The first run usually goes well, but the second time the knee already begins to hurt and the joy of running is gone. Some of the runners keep going nevertheless the pain, some give up the very second the pain begins, thinking “here we go again”. Why? Why is it so that knees hurt while running, but not during other activities?

The reason 1: The tissues aren’t used to it

You haven’t been running for 4-5 months but you decide to start again with a 5-10 km run. You may have been biking and walking during those months, so your endurance capacity is okay and you could manage the run well. Well, it isn’t only about the endurance capacity and your lungs, it’s about other tissues as well. While running, each step brings a hit for your lower limb, which your foot will catch. The hit affects the joints of your foot, but also the joints of your ankle, knee and hip, and if you haven’t been exposed for continuous, long lasting shocks lately, neither your tissues are used to it.

There aren’t any shocks or hits affecting the lower limb while biking and that’s why it’s very “knee-friendly” sport. When walking, the shock is way lighter, since walking doesn’t include the flight phase of running, in which both of the feet are shortly off the ground. If you’re running for 5-10 km, you’ll probably take about 5000-10 000 steps, which means that your knee and the tissues around it are getting that many hits as well.

The reason 2: The alignment of the lower limb fails

The reason for knee pain can also be found from the alignment of the knee and the entire lower limb. Even though the alignment of the knee is perfect while standing or walking, it can change when running, since only one leg is momentarily carrying the entire bodyweight. It’s almost like single leg hopping, the height of the jump isn’t that high though, but the amount of reps is huge.

As the foot touches the ground there should happen some movement in the ankle and the knee, but sometimes the movement is just too large. The knee may sag inwards and if that happens on every step, the result might be pain. The same applies to the ankle: if the foot droops inwards a lot (to pronation), the alignment of the ankle changes, which affects also the knee.

The reason 3: Not enough muscle strength

Believe or not, you need muscle strength for running! If the muscles of the lower limb aren’t trained, the muscles don’t have the power to support the joints for the entire run. That’s when the supporting shifts from muscles to other tissues such as ligaments. You can try what I mean: stand up and keep the weight on both of you feet. Now shift the weight to one foot only and let the other leg relax. You’re now in so called “hip-rest” position, you’re standing on the support of your hip joint and it’s ligaments, not supported by your muscles. The same often happens while running: the beginning of the run is easy and your body is supported by your muscles. Little by little your muscles get tired, even though you only notice that you’re out of breath and your aerobic capacity is getting lower. Now, if your muscle strength isn’t in good shape, your glute muscles may relax for a bit and your pelvis shifts to the side for a bit too much during each step. The hip flexor doesn’t lift your leg up as high as it should, your hamstrings don’t flex your knee enough and the muscles of your shin don’t flex the ankle as much as they should.

Rarely all the muscles of the lower limb of the runners are weak, usually there’re a few muscles that should be strengthened that could affect the knee pain. It’s hard to recognise those muscles yourself, usually you need a professional and a video camera to find them, so that the phases of running can be analyses deeply.

Should I get worried about the pain?

Every one of us have some pain every now and then, and it’s normal. If the pain affects your running a lot or you even need to quit it due to the pain, you should contact a physiotherapist or a running specialist! If the pain is occasional and rare, you don’t need to get too worried, but if the trouble is continuous and occurs on every run, you should get some help!

If you decide not to get help yet, remember these:

In the beginning of the running season, keep the running pace slow
Raise the length of the runs little by little
In addition to running, train muscle strength of the lower limbs