What may affect the knees with running?
- Higher BMI
A prospective study showed that long distance runners among healthy individuals (age 50-72) did not show accelerated signs of radiographic osteoarthritis, OA. Three variables in this study that were found to correlate with the progression of OA over the course of 18 years, equally in runners and non-runners were BMI, initial radiographic damage, and length of time from initial radiographs.
Another large study looking at runners and walkers found that runners had about half the rate of OA in the hip compared to walkers. The walkers in the study were found to be at a higher risk for hip replacement. A lower BMI was associated with less hip OA in runners compared to the walking group.
Even beginner runners for a marathon have been shown to have no greater risk. There was no greater cartilage damage seen in beginner runners compared to more experienced marathoners in a recent study.
As you may imagine, the higher one’s BMI with repetitive impact the legs take when running, the more force their knees have to absorb. This is not to say they should not run, but maybe it is best to keep the mileage lower initially and implement more cross training using a bike, elliptical, or swimming for cardio and strength training until BMI lowers to a healthier level.
So, yes, running does having a higher ground reaction force, though one takes less steps running compared to walking over the same distance. The force with walking is about 3 times your body weight, and with running it is about five to five-and-a-half times your body weight. Therefore, the cumulative force on your knees over a given distance is about the same.
How we run has a huge impact on the stress our knees take with each step. Running occurs in one plane: forward, and the same action is repeated over and over4. Therefore, if the mechanics are off a little, there will likely become a time where a joint or muscle will tell us it has had enough.
Ideally, when making contact with the ground the knee is flexed and the foot is under the trunk of the body, as opposed to way out in front, to help dissipate and absorb the load.
Frequently, it is found that runners have poor trunk and core control and strength, leading to a cascade of events particularly when the body is tired at the end of a long run or race. For this reason, it is important as runners to keep up a regular maintenance program of strengthening and stretching to prevent knee pain.
With proper mechanics, the stress and load from the impact is not directed solely to any one part of the knee. This is likely one of the reasons the studies above do not indicate a direct correlation to running causing or being to sole cause of having knee arthritis.
So, don’t be afraid to get out there and run. Remember to implement strength training and cross training to keep your knees healthy. Stop by one of our clinics and have a video gait analysis performed and learn some proper maintenance exercises if you have had knee pain or think your pain may be due to how you run.