I often get this question: “Doc, does running hurt my knee?” The answer is no. Injury hurts your knee.
If you have healthy knees, you can run forever. If you have a cartilage injury, a torn meniscus, or an unstable knee joint, it will wear out faster than usual.
If you’re a runner or considering taking up running, the following data and insights will help you protect your knees.
Running produces peak impact forces on the knee of one to three times your body weight depending on a host of factors such as the smoothness of your gait, your running technique, and the surfaces you run on. Heel striking increases the peak forces, midfoot-landing produces lower peak forces, as long as the running shoe is soft enough to permit compression of the foot’s arch tissues. Interestingly, when running is compared to walking, since you take fewer steps per mile when you run, the total amount of force that the knee sees is often less in smooth running than in walking. So technique and surfaces do matter.
The healthy knee has articular cartilage covering the bones’ ends in all joints and provides the smooth-bearing surface. The slickness is roughly five to 10 times slicker than ice sliding on ice. When you injure the articular cartilage or get arthritis, this smooth surface begins to get rougher. As the surface roughens, there is a dramatic increase in the friction between the joint surfaces. This increased friction leads to gradually increasing wear of the joint surfaces. During activities, such as running, the damaged surfaces can’t absorb and distribute the impact force from your foot, hitting the ground and standard joint surfaces can. So higher peak forces on an injured knee produce damage.
The healthy knee also has two meniscus cartilages, which distribute forces and stabilize the knee. If torn or missing due to injury or surgery, the impact forces are concentrated on a smaller knee area leading to more rapid wear.
Lastly, the healthy knee has ligaments that stabilize the knee. Unstable knees lead to tearing of the meniscus, and just like a car out of alignment wears out its tires, the abnormal motions of the unstable knee lead to an acceleration of the wear patterns of the joint surfaces.
The assertion that healthy knees can run forever is backed up by observations of huge animals such as African elephants weighing more 13,000 pounds that can run extraordinarily fast, and live for 60 years without joint arthritis.
We have also found that people can return to running even after injury by repairing their articular cartilage and replacing damaged meniscus cartilage or ligaments with donor tissue. A long-term outcome study of some of our biologic joint replacement patients found that many were able to run again after fearing that they had reached the road’s end.
Nothing beats running. Running provides the endorphins, pheromones, adrenaline, and testosterone so efficiently that the addiction to running and the bliss from it is challenging to replace. Running provides a health benefit based on a cost basis and time analysis that any healthcare program envy.
If you have healthy knees, run, but make sure you run efficiently with a smooth technique involving short strides, midfoot landing, well-fitting running shoes, and soft surfaces. If you have injured knees, repair them or find the running bliss in other sports, but don’t miss out.