“I love running, but I know it’s bad for my knees. I keep thinking I should give it up.”

It’s something I hear often from my clients. The idea that running is bad for the joints, and that “low impact activities” are better for you, is a prevalent one. Even medical professionals sometimes still advise people worried about their knees to stick to swimming or cycling.
How much truth is in this, though?

Runners don’t have particularly unhealthy knees

A study published this year showed that although plenty of runners did get knee pain and osteoarthritis, non-runners were even more likely to suffer from these problems. If you run and you have knee pain, it’s natural to blame the running (after all, that’s when you might be most aware of it); but this study suggests that may not be the cause of the problem. People who had run regularly in the past, but not currently, had healthier knees than non-runners but less so than those who are currently running.
A review in 2011 looked at the effects of physical activity on the knee in general. Many of the studies reviewed looked specifically at runners; others considered a range of other weight bearing activities. Overall, it found that although the more active participants showed some increase in the formation of osteophytes (bone spurs), they also showed no evidence of joint space narrowing (a hallmark of osteoarthritis) and healthier cartilage than their less active counterparts. Although osteophytes are sometimes associated with damage to articular cartilage, the authors argue that they can also be seen as a normal response to mechanical stress, that needn’t be regarded as problematic.

So, running is good for your knees…?

Whoa, hold on… not so fast. Remember that problem we keep running into with these studies? Correlation is not the same as causation. All we know is that people who choose to go running (or have done in the past) have healthier knees than people who don’t. But runners are a self-selecting group, and it might just be that people who have less knee pain are more likely to go running in the first place. Equally, people who have had knee injuries in the past (which we know is a risk factor for osteoarthritis) might be less likely to run because they’re (rightly or wrongly) worried about developing problems in future.

Another confounding factor could be body weight. One survey published in 2013 noted that running’s apparent protective effect when it comes to hip OA is in part due to its association with lower BMI. As knees are also known to be affected by excess body weight, it would seem reasonable that BMI might also mediate the effect of running on knee health. So – running helps you lose weight, which protects your joints? No! Or at least - not necessarily. If you’ve been paying attention, you can probably guess what comes next: correlation is not causation. Instead of running causing the lower BMI, it might be that people with a naturally lower BMI are more likely to take up running. In fact, there is some evidence that activity alone might not have as much of an effect on weight loss as it’s sometimes given credit for.

That all sounds a bit vague. Can’t you just give us a “yes” or “no”?  

How hard could it be to get a definite answer, without all the “perhaps” and “maybe”? Very hard, as it turns out. The only way we could establish whether or not there’s a bona fide causal link between running and knee pain would be to randomly divide a number of volunteers into two groups, assign one group to run regularly, and insist that the other group do not. Then – and here’s the difficult bit - you’d have to (somehow) ensure that the groups stuck to these instructions for years, while you monitor them for signs of knee problems. If anyone ever finds a way to persuade average people to stick to an exercise plan consistently over the long term, they’ll make good money selling their secret; until that time, we have to look at the evidence that’s available and interpret it as sensibly as we can.

What if I already have knee problems? Is it okay to keep running?

The answer to this will depend on exactly what is wrong with your knees. I’d strongly recommend seeing a qualified professional to get a proper diagnosis and individual advice. In general, though, we know that movement and activity are actually good for many kinds of joint problem. Running should not be automatically discounted if it’s something you want to do.

The advice for osteoarthritis sufferers in particular has changed significantly in recent times, and patients are now advised that staying active is likely to be helpful rather than to cause more damage, as many fear. This is true even if activity is somewhat painful, although it’s important that you speak to your doctor or clinician to find the right balance between managing your pain and staying active.
Even for patients who have had a meniscectomy (partial meniscus removal) – a group who are known to be at a higher than average risk of developing osteoarthritis later in life, and who may in the past have been advised to limit the amount of running they do – it isn’t clear that doing so is always necessary.

The verdict: probably FALSE

The evidence points towards running – at worst – not being bad for your knees, and it may even be beneficial. It’s also important to remember the numerous benefits runners get from it, including improved general health and enjoyment. Even if running did slightly increase your risk of knee problems (and the evidence at present suggests that this is unlikely), overall it almost certainly does you considerably more good than harm.