Is Running Bad for my Knees?
One of the most talked about joints in running injuries is the knee. A common concern is that people either have a history of knee pain or have been diagnosed with arthritis and they fear that running will make the pain worse. I often hear people say that they don’t run at all because it’s bad for the knees. Recently, there have been two articles in the New York Times that have peaked my interest. They address and even challenge previous thoughts that running increases the risk of arthritis and places too much stress on the knee.
I’m not saying that everyone that has ever had knee pain or has arthritis should suddenly start running and they will be cured, but the studies discussed in the articles raise interesting points to consider.
Running and Force Distribution
A recent study done in Finland and published in Medicine & Science in Sports & Exercise looks at not only how much force is transmitted through the body during running, but where exactly are those forces hitting the hardest. The age old question of whether it is better to heel strike or forefoot strike while running is addressed. Unfortunately, there is no real answer to this question. However, the results do confirm that heel striking increases the forces transmitted to the patellofemoral joint (where the knee cap meets the knee joint). On the other hand, there is just as much force absorbed by the body with forefoot striking, but most of that force goes to the ankle and Achilles tendon.
One of the more interesting points from this study was exactly where the forces were being transmitted through the knee joint. It was found that the majority of force is absorbed by the knee cap (patella) and the medial (inside) aspect of the knee. These two locations are where the common condition of Runner’s Knee, or patellofemoral pain syndrome, presents itself.
So which is better, heel striking or forefoot striking? A key takeaway from this is that if you have knee pain, switching your running form to more of a forefoot strike may help to reduce the forces in the knee.
What about knee arthritis? Since there is so much force absorbed by the knee with a traditional heel striking pattern (how most people run), it has been thought that running must be bad for the knees and even cause arthritis.
The results of a large cross sectional study of 75,000 runners suggest that running does not increase the risk of osteoarthritis compared to walking. How is this possible if we know that running loads the patellofemoral joint and we strike the ground with 3-5x our body weight when running?
A new study out of Queen’s University in Ontario looked at the loads applied to the knee joint over a given distance, or per unit distance (PUD). There was no significant difference in the PUD loads in running versus walking. The theory is that the shorter ground contact time in a running stride versus a walking stride helps to off-set the high loads applied to the knee during running. So while a runner generates more force with each stride than a walker, they take fewer steps over a given distance, which helps to decrease the overall force applied to the knee. A takeaway point from this is that in a healthy knee without pre-existing osteoarthritis, running is no more likely than walking to cause the onset of arthritis.
Positive Effects of Running on Arthritis
There are even a few variables that suggest running might actually help prevent arthritis. Body Mass Index (BMI) is found to be related to the onset of osteoarthritis (OA). A higher BMI increases the risk of OA. Running has been found to be associated with a lower BMI, therefore, lowering the risk of OA due to high BMI.
Another factor in support of running for knee health is the concept of cyclical loading. In animal studies, it has been found that cartilage responds well to forces applied to the joint, removed, then applied again; similar to the forces of running. The cartilage response has been for the cells to divide and replenish. While this is an encouraging finding, it is still far from being definitive.
So after all that scientific talk about the results of studies, is running bad for our knees or what?
I think we can safely say that running applies force to the body and It is suggested that striking with more of a mid-foot strike versus a heel strike can help to reduce forces that contribute to patellofemoral pain syndrome. If you want to run for exercise and are worried about your knees, it might not be as harmful as we once thought. In fact, if running is going to help lower your BMI, it can actually benefit you in many ways including a potential reduced risk of OA among other chronic illnesses associated with high BMI.
So, go ahead, keep running (or start running)!