Why don’t most runners get knee osteoarthritis? This question was posed in a research paper, which appears in the March issue of Medicine & Science in Sports and Exercise — the official journal of the American College of Sports Medicine.
“Most studies on humans have concluded that long-distance running is not associated with an increased risk of knee osteoarthritis. This is not to say that runners are less at risk for knee osteoarthritis compared with non-runners. However, they do not appear to be at greater risk,” noted the research.
Osteoarthritis, according to the Mayo Clinic, “is the most common form of arthritis, affecting millions of people around the world. Often called wear-and-tear arthritis, osteoarthritis occurs when the protective cartilage on the ends of your bones wears down over time. While osteoarthritis can damage any joint in your body, the disorder most commonly affects joints in your hands, neck, lower back, knees and hips.”
It appears that chronic high knee loads (between surfaces within the knee) are suspected to a play a role in the initiation and development of knee osteoarthritis. Here is where the paradox between walking and running takes hold.
How can it be that walking — with peak knee joint loads of two to three times body weight — may play a higher role in the development of knee osteoarthritis, compared to running — with peak knee joint loads in excess of eight times body weight?
The answer appears to have something to do with not only the peak load, but also the duration and magnitude of the “cumulative loading of the knee and other joints.”
The researchers “wondered if the biomechanics of running protect the knee from peak loads that would otherwise be highly injurious if they were encountered during walking.”
Using fourteen healthy adult males and females, who were recreationally active around the age of 25 (+/- 11 years) and with no history of major knee trauma or events in the past year, the researchers compared their “peak and per-unit (PUD) knee joint loads between walking and running.”
Participants were instructed to achieve a walking speed that one might use “walking down the street,” while the running speed was one that the subject would use to “ jog for exercise.”
The researchers found that, “the duration of the load application and the distance covered per loading cycle offset the relatively high peak joint load of running, such that the load accumulated per unit distance traveled is no greater in running than it is in walking.”
In other words, the running gait — with the longer swing phase of the legs, as well as, the time off the ground (flight) during running, which is absent during walking — lessened the load on the knees.
In essence, the load duration and stride length during running may have “blunted the effects of peak joint contact forces that would likely be highly injurious if they were encountered during walking.”
Whether the running was at slow, moderate, or fast distance speeds, the so-called “blunting effect” suggested that, “runners may be able to increase their average training speeds without increasing their risk of knee osteoarthritis.” As appropriately noted, this conclusion needs additional validation.
According to John Burvant, an orthopedic surgeon affiliated with the Pontchartrain Orthopedic and Sports Medicine Clinic, “the results of this study are counterintuitive to what you would expect with the development of osteoarthritis. More research and study needs to be done to see if the results hold true.”
A word of caution is warranted. “This conclusion likely does not extend to running injuries in general. However, running actually induces a positive remodeling of the knee cartilage compared with a sedentary lifestyle,” stated the researchers.
As Dr. Burvant suggested, with time, research, and study, we will come to understand more about how we can live a productive and healthy life through fitness activities like walking or running.
