There is a general perception that running is terrible for the knees and that sooner or later, if you keep running, you will get injured. The next time someone tells you that, answer them with certainty (and with the support of science) that your runner's knees are stronger than theirs.
The theory that running is harmful to the knees has its logic. After all, in an hour of jogging we strike the ground about 5000 times with each leg, which results in 5000 impacts to the knee. If we run from Monday to Saturday, by the end of the week we will have struck our legs against the ground about 30 thousand times.
After so many impacts, bone tissue suffers micro-injuries due to the impact, even though it doesn't hurt at the moment. What defenders of the myth don't know is that the body recovers from micro-injuries and not only leaves the tissue the same as it was before the jog, but—and this is the best part—rebuilds it even stronger.
Researchers have found that the constant loading and unloading of the knee joint caused by weight-bearing activities, such as running, helps strengthen it. Additionally, the flexion and extension of the joint causes fluids to circulate that lubricate and nourish nearby tissues.
At Stanford University they conducted a study with a group of runners and another group of sedentary people, all over 50 years old. They monitored them for 18 years assuming that the runners would end up suffering more from osteoarthritis than the sedentary group, precisely because of the impact they subjected their bones to when running. Imagine their surprise when 18 years later the group of runners had healthier and stronger knees than the sedentary group, and the sedentary group also showed higher rates of osteoarthritis.
But—and this is an important but—not everything is so easy and good. When there is a condition that causes uneven loads on the knee, inappropriate wear will occur and therefore the risk of injury will increase.
Poor foot support, an incorrect stride pattern, previous injuries, or muscle imbalances generate uneven loads and increase risk. Especially the quadriceps (the muscles in the front of the thigh) and the hamstrings (the muscles in the "back" of the thigh) are important for knee health, so developing strength, flexibility, and proper balance in these muscles will help you stay injury-free.
Activities like swimming, cycling, yoga, pilates, and weightlifting are excellent to complement your running training program. Including some of these alternative sports will help you reduce the risk of all typical runner injuries. Gradually increasing your mileage (no more than 10% per week is a good guideline) and allowing 2 or 3 days each week for rest and recovery will also help you prevent injuries. Make sure your plan is created by a qualified person. (Find out what the six signs your trainer is bad).
The important thing is to break that myth that running is bad for the knees. When loads are well distributed and balanced and you follow a plan with appropriate rest periods, the body responds well to stress and actually strengthens. Your whole body, knees included. So enjoy your runs and age with healthier and stronger knees.
Sources: Stanford University Study; McArdle, Katch and Katch, Exercise Physiology, 6th Ed.; Tucker and Dugas, The Runner's Body; Runners World.
