When we first opened the company, Dr. Slavko and I had a lot of time on our hands. We spent those first weeks marketing our butts off. We still do, but not to the extent we did back then. Many days were spent cold-calling physicians and local businesses to let people know we existed.
One thing, though, still sticks with me from those early days. A number of local businesses were also focused in the health and wellness realm. And on more than one occasion, trainers in the businesses we visited mentioned how they were fans of physical therapy and how their activity was good for the body because it was low impact. They made a point to highlight low impact. Saying it multiple times.
Why did they say that? Do they actually believe that loaded activity is dangerous for the body? Where does the fear come from? Were they just trying to say things they thought would appeal to us as therapists (for a potential gain in cross-referrals)? Is that what they think of physical therapy, just some low intensity table exercises? This has been bugging me over the last few months. I think the thought process behind those interactions stems from a fear that impact activity causes joint degeneration. Rather than going on a rant, let's go to the research to see the real relationship between impact activity and arthritis.
Osteoarthritis (OA) and Running
Let's get right to it. Runners do not have an increased risk of developing knee OA compared to non-runners. Here are some proposed mechanisms for why: 1) Despite high peak loads during impact, the load is only experienced by the joint for a short contact duration. 2) The surface area of joint contact is likely greater in running than walking, meaning the forces gets dispersed. A certain amount of kinetic energy concentrated focally, can certainly be damaging. But spread out over a larger area, it's a non-issue. This is what likely happens when running. Back to the first mechanism: due to the flight time in the running cycle, the force experienced per unit of distance or time is low.
Intermittent periods of high force are okay, even beneficial if performed with an adequate period of relative rest, to allow for adaptations to occur. That's basically a description of strength training, by the way. The human body needs force to adapt and get stronger. Cartilage and connective tissue adapts to force as well. Not just muscles. This study showed weightlifters to have significantly thicker knee cartilage in an age and BMI matched control group.
*Here's the caveat (there is always a caveat. Also, never use absolutes):
I can't find the source right now, but I remember recently reading that there was no association or increase in risk of OA for runners, unless they were training at elite levels. I'm talking consistently >60 miles or so a week. Again, take it with a grain of salt because I can't find the source right now, but I will include it here when I do. And there is also evidence that long distance running can have a protective effect against degeneration.
OA and Impact Sports
Do other sports cause OA? Well that depends. For the vast majority of people the answer is no. Soccer athletes (elite and non-elite) do show an increased risk. For elite and professional level athletes, the answer is still, generally, no - it will not cause joint degeneration. However, there is evidence for an increased risk of developing OA in the knee or hip. But be mindful to realize that does not imply causation.
If you do any of these activities and you develop OA, that doesn't mean the activity caused it. There are likely are other risk factors responsible.
-Dr. Piotr