Very high and very low levels of physical activity can both accelerate the degeneration of knee cartilage in middle-aged adults, according to a new study.Researchers Thomas M. Link and colleagues tracked changes in the knees of 205 adults (45-60 years of age, with no knee pain reported at outset), using MRI exams over a four-year period. The result: Subjects who participated more frequently in high-impact activities (such as running or playing tennis) or who were sedentary had their knee cartilage degenerate more than those who were moderately active physically.
Before we go further, I have to include a disclaimer: Once again, I couldn’t access the full study. So, for instance, I don’t know exactly what “moderate activity” means, which is annoying. But from context I’m going to guess it translates into lower-impact exercise, such as swimming or walking.
What I like most about this study:
* It shows (yet again) that being sedentary is bad for knee joints.
* It underscores my belief that there are joint-friendly exercises (assuming I’ve interpreted “moderate activity” correctly), such as walking. They combine high-repetition and low impact, and subjects in the "moderate activity" group saw little change in their knee cartilage over four years.
* The study looked at subjects with a BMI of 19-27, thus excluding overweight to obese knee pain sufferers. This makes the results cleaner to analyze.
What I like least about this study:
Basically, one thing: the insinuation that hard exercise will ruin your knees. I just don’t think this is true. Earlier, I wrote about a study that showed that longtime marathon runners -- a group that, if any, should have creaky, decaying knees if high-impact sports are bad -- were found to have better joints than non-runners.
Then, there’s this article, saying that “recent research finds jogging might be good for your knee cartilage and joints.”
It cites a Swedish study that discovered that the biochemistry of cartilage improved in the knees of runners vs. non-runners (the belief is that the high impact occurring when your feet strike the ground increases the production of proteins that make cartilage stronger). Other studies (one of Massachusetts residents, and one by Stanford University) concluded that runners were no more likely to develop arthritis than non-runners.
So does this mean there’s no objective, found truth on whether vigorous exercise helps or hurts or does neither? Where does the truth lie?
This is what I think:
If you are older (say between 45 and 60, which was the age range for the subjects in Link’s study), you must exercise smarter if you’re going to do high-impact sports. If you’re going to do low-impact, lower-intensity activities (such as walking), you can afford to be dumber about your approach.
What do I mean by “exercise smarter”? Well, (1) maintain a healthy weight (2) warm up before working out (3) be fairly consistent in your routine.
Number 3 is very important, in my estimation. It means don’t start running twice your normal distance, for example, without giving your body a period of time to adjust. It means don’t think you can hike uphill six miles without problems just because you play a lot of tennis and you’re fit.
Yes, your knees can adapt to more stressful demands put upon them. (The reason marathoners don’t have knee problems, it has been hypothesized, is that the joints get into a “motion groove” where they acclimate to the rigors of long-distance running.) But the adaptation is best when gradual and consistent (don’t run as if you’re training for a race in June, vegetate for July and August, then in September try to resume where you left off in June).
Maybe I’m a dumb optimist, but I think you can be a 60-year-old marathoner with perfectly healthy knees. You just have to be smarter about it than the guy who enjoys walking for exercise.