Knee Forces


PART 2: A Look at the Impactive Forces on the Knee

Recreational Jogging seems harmless enough. A few miles here and there, it keeps you healthy, it's fun to be outside, and every fitness magazine out there says it's imperative to health and losing weight. Taking a look at the mechanics (and habits) of running paints a different story, a story of repetitive stress and excessive forces the body has to deal with. Too long of distances, not enough recovery time, and using running as your go to form of exercise promotes detriment directed at the knee joint.

I wrote an article on the Physiological detriments a while back which can be found HERE

Jogging increases forces from 2-3 times bodyweight compared to walking. An average runner, say 5'8" 150 pounds, takes approx 400 strides and foot strikes in a mile which translates to roughly 60-90 tons of force; a tremendous amount of force for the body to incur, absorb, and dissipate. Plug that into an average week's worth of running, say 40 miles, and you have 16,000 strikes with 2400-3600 tons of force. That's a lot of force entering the body! Each person has a different running style or gait, a different makeup, stride length, height and weight etc., so those forces could be lower or higher, but the point is that this simple form of exercise can be a major source of degeneration on the knee joint if not managed correctly. Like it or not, the reality is that running can translate into a significant amount of repetitive stress on the body which can increase the likelihood of injury. The human body is simply not engineered to be an endurance machine.

Different methods of running have been analyzed which reduce force such as landing more on the mid foot as opposed to the heel, shortening stride length, and keeping a slight bend in the knee at impact. This article goes into great depth should you want more info.

Overuse & Injury
The knee joint is subjected to repetitive impact from running and resulting impact forces which develop high amounts of stress that can negatively affect the structure of the joint. "In response, the knee joint’s ability to handle this stress intensification decreases in the face of the load accumulation. This self-defeating condition persists until the structure fails and and/or injury develops." Any joint subjected to overuse, overload, with little recovery time, and poor nutrition habits is sure to degrade. (Bench Pressers beware!) The knee is the primary shock absorber in walking, jogging, and running, and as stride increases, the forces it must dissipate increase. Avid runners should be aware that although a natural human motion, running should not be considered a sole source of exercise for the detriments mentioned above. Incorporating resistance training, intervals of brief duration, and low-intensity long walking all allow variation and rotation to the knee joint in which it is targeted and strengthened differently.

Bobbert, M.F., H.C. Schamhardt, and B.M. Nigg: Calculation of vertical ground reaction force estimates during running from positional data. J. Biomech. 24:1095-1105, 1991.

Sol, Costanza: Impact Forces at the Knee Joint – A Comparative Study on Running Styles


Force Plate Analysis

Torn Cartilage