Is running going to ruin my knees?


“Oh you run, that must be bad for your knees!”

“All that running you do, you’ll be a cripple when you’re older...”

Many things I hear regularly as a physiotherapist and a runner are purely folklore, with no scientific evidence to back them up. In this blog we’ll be looking at one of the most frequent examples: I hear time and again that running is bad for your knees.

It’s true that one of the main reasons people stop running is knee pain (one study of marathon runners showed that 42% of those who had stopped running did so due to knee pain). However, there are some more positive results from other studies of runners. One showed fewer hip and knee replacements in runners than non-runners, another showed that runners were significantly less likely to develop knee arthritis than walkers. The main reason for this may be that the runners had a lower BMI (more on that later). 

Taken as a whole, research in this area has not delivered any conclusive scientific evidence that running is bad for your knees. Some scientists even postulate that it may be good for your knees, though we are a long way from proving this. 

“Will the repeated impact from running damage my knees?”

You can see the logic. All those repetitive impact forces - every stride a runner takes, pounding the pavement, the poor old knees soaking up the impact, destroying the cartilage bit by bit until he or she is a dead cert for arthritis. But impact itself is not something to be feared. On the contrary, impact is vital for the health of our body. To take an extreme example, astronauts take months to recover when they return to earth due to the lack of impact on their bones and muscles during their space missions, which causes significant weakening of the tissue. It’s impact on the tissues of our body that prompts a reaction from these tissues, causing them to adapt and strengthen in order to be more prepared for the next impact.

The illustration above demonstrates the importance of maintaining a balance between load and adaptation. Not enough impact or too little stress on the tissue and the tissue will waste away or become weaker. Too much impact or stress with too little recovery time to adapt and you will risk damaging your tissue (injury). How much stress and impact your joints can take and how much recovery time you need depends on many factors - your genetics, how active you have been through your life, how active you have been recently, how well you sleep, how stressed you are. 

If you’ve been sitting on the sofa for the last 5 years then the impact of walking 5km can be extremely challenging. If you regularly run 50km a week then an easy 5km run will put minimal stress on your joints. 

“If I’m overweight, will running be harmful for my knees?”

What is evident from research is a clear correlation between being overweight and knee joint arthritis, and obesity is the number one preventable risk factor for osteoarthritis. For years this was indeed assumed to be due to the extra weight overloading the joints but research is now showing a link between increased fat cells in the body and joint inflammation and arthritis. 

Fatty tissue is home to millions upon millions of busy fat cells. These fat cells respond to high levels of glucose by producing immune proteins called adipokines. These proteins in turn cause a low level chronic inflammation in tissue, resulting in arthritic damage to joints. You can read more on this here.

On this note, over the last two years I have had the privilege of working with a Couch to 5K group and seen some of them using running as a way of loosing weight and then catching the running bug. These new runners end up feeling fitter, stronger and healthier than they have done for years. A side effect of all this is that they also lose weight, which we know will in turn reduce the risk of arthritis. 

“I’d love to run, but I can’t because my knees already hurt.”

Many people with existing knee pain or who have had to give up running in the past believe they’ll never be able to start or return to running. In some cases this may be true, but without trying they’ll never know. The key is to ensure a base level of strength and fitness first - this can be achieved through other forms of exercise like walking, cycling, swimming, strength work - and then start with a very small dose of running, slowly building up as your knees adapt. This process is easiest with guidance from a good physiotherapist or coach who can work with you to find the right starting point and the right speed to build up and will then be able to guide you through the inevitable setbacks you will experience along the way.

So, in conclusion, great news - running itself won’t hurt your knees! He’s a summary of my advice when it comes to knees:

Runner, no knee pain
Great! Keep on running 😊 There’s no evidence you’re damaging your knees.

Runner, knee pain
If you notice correlation between running and increased symptoms, it’s worth seeing a physio for guidance on how to manage your symptoms.

Non-runner, no knee pain
It’s fine to get started as long as you manage the load carefully, in accordance with your current fitness and activity levels.

Non-runner, knee pain
Knee pain doesn’t mean that you can’t start running, but it is best to seek advice from a physiothereapist before you start.