"No, I don't run. It's bad for the knees"
The title of this blog post is fake news. Very fake news. Nobody loves to run more than I do and by the time you have read this, you’re going to love running too. You’re going to get tired of how much running you will do. This blog post will Make Running Great Again.
OK, on to the evidence…
“Injury” can be summed up in a simple sentence: The load applied to a tissue has exceed the capacity of that tissue to withstand that load.
Stand in front of a speeding bus, and the load that the bus imparts on you will exceed the capacity of many bones and ligaments to withstand that load. There is a not so lovely example of a traumatic injury.
Non-traumatic injuries can occur as well. For example – we’ve been told that if you run enough miles in your life and your knees will degenerate. It’s a small load, but done enough times, the cumulative load will exceed the capacity of the cartilage in your knee and the cartilage will break down. Sounds reasonable, right? Fortunately, it’s not reality. At least, it’s not the total reality, if you’re smart about your training. If you agree with the statement that running will cause your knees to degenerate, you’re forgetting that we are adaptive, living beings. We are not mechanical. Mechanical models and biologic models are quite different. Let me explain:
If you drive your car around enough, the parts in the car break down through wear and tear. The parts do not adapt to the load being applied to them and they weaken and break down. That is the mechanical model.
Humans, on the other hand, are biologic. We adapt. If you go to the gym and lift weights, do your biceps wear down? No, they get stronger. If you are at risk of osteoporosis, you are told to increase your bone density by doing some weight bearing activities. Doctors know that bones adapt by increasing density to become stronger. This is the biologic model.
Because we are in the biologic model, we need to put an addendum on the end of the definition of an injury. It should read: The load applied to a tissue has exceed the capacity of that tissue to withstand that load. However, the capacity of the tissue will increase if the load approaches, but does not exceed the tissue’s tolerance.
So, why do doctors and many people not have the same attitude about knees and cartilage? Cartilage CAN adapt too! When it comes to the shape and healing, cartilage is much less adaptive than other tissues in the body, but it can certainly change is composition in a positive, healthy way.
For example, we know that when mechanical loading is taken away or diminished, cartilage becomes unhealthy. It actually becomes thinner [1,2,3,4]. Research also shows that cartilage thickness increases with increasing physical activity in children [5,6] but maybe not in adults . This is a bit conflicting, since it has been shown that knee cartilage is thicker in marathon runners compared to non-runners , although this was an observational study, so maybe those runners were running because they had thicker, healthier cartilage to begin with? This is the problem with this type of research.
However, that is with respect to cartilage thickness…
There is more to cartilage health than thickness. Cartilage composition is also important. Without getting too much into the detail of cartilage, it is made of cells called chondrocytes with an extracellular matrix. Within the extracellular matrix are glycosaminoglycans (GAGs) which contribute to the strength of the cartilage and also attract water in the cartilage. Van Ginkle et al., found that after only a 10 week “start to run” program, there was a significant increase in GAG content in the knee cartilage in the runners when compared to a similar group of subjects that didn’t run during that 10 weeks. They found this by taking MRI’s at the beginning and end of the 10 weeks. Tiderius et al., also found higher GAG content in runners compared to non-runners, and several animal model studies also support this [9, 10, 11, 12]. Therefore, it would seem that running positively alters the composition of the knee cartilage, despite the evidence being inconclusive when measuring thickness of cartilage in runners compared to non-runners.
In addition, a recent meta-analysis (pooled data from previous research papers) found that runners have a 50% less chance of ever undergoing knee surgery due to arthritis . We also need to take into account that one of the biggest modifiable risk factors for developing arthritis in the knee is being overweight – even more so than the non-modifiable risk factor of genetics . So if a high BMI is a big risk factor for developing knee arthritis, and running is a way to exercise to reduce BMI, and we know running improves the composition of cartilage, wouldn’t it be logical to run? One could argue that other, less mechanically stressful forms of exercise could do the same thing, but the mechanism thought to improve the composition of cartilage is the compressive, load bearing mechanism . You just don’t get that with swimming or biking.
Runners often tell me they can’t run because they feel pain in their knees. Again, this is often due to the application of the load. They are running in a manner that loads the knee excessively, or their training methods were poorly applied and the tissue didn’t have time to adapt. There are ways to remedy these problems.
In conclusion, research thus far has generally shown no negative association between long term distance running and knee arthritis, despite widespread public opinion that “running is bad for your knees.” Don’t believe the fake news 😉