iIn the annals of unsolicited advice, few nuggets have been dispensed as widely and with less supporting evidence than this: “If you keep doing all that running, you’re going to ruin your knees.”

The latest salvo in the debate over knees and running — a systematic review of 43 previous MRI studies that find no evidence that running causes either short-term or long-term damage to knee cartilage — is unlikely to convince the opinionated ex-football star at your Thanksgiving table who swears his bum knee was caused by wind sprints. But given that nearly half of Americans are expected to develop painful knee osteoarthritis at some point during their lives, the findings do raise a nagging question: If abstaining from running won’t magically protect your knees, what will?

Researchers have lately begun to rethink long-held dogmas about the properties of cartilage, the smooth layer of tissue that cushions the bones of the knee and other joints and whose breakdown is the primary cause of osteoarthritis. “Since cartilage doesn’t have a blood or nerve supply, we used to think it couldn’t adapt or repair itself,” said Michaela Khan, a doctoral researcher at the University of British Columbia and the lead author of the new review on running and cartilage, which was published in the journal Sports Medicine.

But that’s not the case. Cyclic weight-bearing activities like walking and — wait for it — running squeeze the cartilage in the knee joint like a sponge, expelling waste and then drawing in a fresh supply of nutrient- and oxygen-rich fluid with each step. Instead of an inert shock-absorber doomed to get brittle and eventually fail with age, Ms. Khan said, cartilage is a living tissue that adapts and thrives with regular use. That explains why, for example, in a small study from 2010, non-runners who followed a 10-week running program saw a 1.9 percent improvement in a marker of cartilage strength and quality.

It also helps explain why swapping one form of exercise for another at the first sign of knee pain may be counterproductive. People with incipient knee problems often switch to low-impact activities like swimming and cycling because they believe it will protect their joints, said Jackie Whittaker, a physical therapist, and arthritis researcher also at the University of British Columbia, “but actually what they’re doing is starving the cartilage.”

Still, there’s a limit to how quickly the joint can adapt to unfamiliar stresses. Jean-François Esculier, head of research for The Running Clinic and Ms. Kahn’s co-author, suggested that knee pain that persists for more than an hour after exercise, or that shows up the morning after a workout, is a sign that the joint was overloaded. That doesn’t mean you need to stop exercising, he said, but that you should adjust what you’re doing.

Consider shorter and more frequent workouts. According to Keith Baar, a physiologist at the University of California, Davis, who studies the molecular properties of cartilage and other connective tissues, the cells in cartilage respond positively to exercise for about 10 minutes. After that, you’re just accumulating more stress and damage in the tissue with no further adaptive benefits. So, if a weekly two-hour tennis marathon leaves you with aching knees, you might try swapping it out for one-hour sessions twice a week.

Of course, no workout takes place in a vacuum: What your knees can handle today depends on what you’ve been doing with them over the preceding weeks and months. That’s why the arrival of ski season is a source of predictable carnage for physical therapists, as enthusiastic weekend warriors hit the slopes after months of inactivity.

Dr. Whittaker suggested taking the first day on the slopes easy and being willing to cut subsequent days short when it feels like your leg muscles or joints have had enough. “It’s pacing,” she said. “It’s adapting to the capacity of your body to handle the load.”

Better yet, she strongly suggested doing some strength training to prepare your legs before putting any new stresses on them. A simple, generic program of squats and lunges can strengthen the muscles that keep the knee stable and stiffen the tendons and ligaments around the joint. For starters, aim for three sets of 10 to 15 repetitions, lifting a weight that leaves you with shaky muscles and the feeling that you could have done two or three more reps if necessary.

Full article: https://www.nytimes.com/2021/11/19/well/workout-exercise-knee-health.html

The New York Times

By Alex Hutchinson