For many runners, with every bit of pain they experience, their knees can feel like a time bomb slowly ticking down to zero. Just as some people think the heart only has so many beats in it, do a runner’s knees only have a certain number of miles in them? If so, what’s that limit? How many miles can a person actually run before their knees turn to calcified dust? Can you run every day, or should you rest?
Alongside James Ficke, we’re pounding out some answers. Ficke is orthopedist-in-chief at Johns Hopkins Hospital and a professor of orthopedic surgery at Johns Hopkins Medicine — he’s also an ultra runner himself, and he racked up 2,200 miles last year (averaged out, that’d be six miles every damn day).
What can I expect from my knees? Can I run every day, or should I rest them?
Unfortunately, there’s no one answer. “Not every person is going to be able to run for a lifetime,” Ficke says. There are several reasons for this (more on that in a minute), but there’s also good news, for a few of us at least: There are some people who can run their whole lives.
Ficke says there’s a lot of data that’s been published about that, and that people with intact knees — meaning they’ve had no fractures or ligament injuries — can often run their entire life. “If you’re talking about someone running on a knee that hasn’t been injured, they can do it till they’re 90 and not have an increased risk of arthritis,” he says.
How do I keep my knees intact, then?
Avoiding injuries is a big one, because knee injuries can open the door later for arthritis. If someone’s had a fracture or torn a ligament (which is awfully common in knees) it can lead to what’s called post-traumatic arthritis.
As Ficke says, there’s no one flavor of arthritis: What happens in post-traumatic arthritis is that that joint develops an irregular surface, which begins scraping like a file on the other side of that joint. You can imagine where this is going — it eventually wears out the smooth cartilage in the joint. “This is what we call wear-and-tear arthritis, or degenerative arthritis,” Ficke says.
But immune diseases can also lead to arthritis. There’s rheumatoid arthritis, for example, and there’s also Lyme arthritis from Lyme disease. In these cases, it isn’t pretty inside your joints: Rather than scraping cartilage off like a file, inflammation causes your cartilage to basically dissolve.
So what’s all this mean for my sweet, sweet baby knees?
It means that when that smooth cartilage surface is taken away, your joint stops functioning so well. Ficke likens a healthy joint to the frictionless way an ice skate glides across the ice. Likewise, when you’re running with healthy joints, the knee is gliding, the hip is gliding, the ankle is gliding. But when the surface becomes rough, cartilage starts to wear out increasingly faster.
How common is this?
Ficke says that only about six percent of the population under 50 has knee arthritis. But when you reach 50, that percentage starts to increase (this can happen even if you’ve never had a knee injury). But in any case, as you get older, your cartilage starts to degrade. Some people will get it worse than others: Some can still run, others not so much.
It’s unfortunately also a function of genetics. “There will be some people running when they’re 40 and they have arthritis. And there’ll be some people that are running when they’re 80 and they don’t,” Ficke says.
If that happens, does that mean the end of me running?
Actually, no. You can mitigate it through strength training — in fact, you should be doing this anyway. “Every person who’s a runner should know that they need to maintain muscle strength,” Ficke says. “If a person’s running seven days a week and not doing any kind of strength training, then they’re at risk for having knee pain or injuries.”
But not all knee pain is arthritis, right?
That’s right — patellofemoral syndrome, or runner’s knee, is one of the most common running injuries. That’s when the kneecap doesn’t always glide smoothly as the knee flexes, due to misalignment or some other issue. Sometimes it can be cured or at least mitigated by specific exercises that strengthen muscles around and behind the knee. Other times, Ficke says, you can end up with a temporarily sore knee simply from having an off day.
What about surfaces?
Yep, the surface you run on can make or help break your knees. Ficke says it’s much more common for a knee to wear out by running on concrete (in addition to suffering other overuse injuries). “If you’re running on terrain like grass or trails, the incidence of arthritis or the incidence of problems relating to that kind of running are much less,” he says. The scale of surfaces from most punishing to least is something along the lines of concrete, asphalt, wood or hard surface, trails and grass (with a running track somewhere in the middle). Wearing properly cushioned shoes that still have some spring in them obviously helps too.
Another element is rest. Even ultra runners who do two running workouts in a day will have many hours of rest in between where they’re completely off their feet, giving a break to their joints.
Those people who run at 80: What’s their secret?
First and perhaps most importantly, Ficke says, they didn’t suddenly start running at 80. They’ve been running for years and have learned how to negotiate minor injuries and how to care for their bodies. Their muscle mass and bone density is reasonably high. They’ve also learned to adapt: They’ve slowed their paces down from how fast they ran in high school, they’re increasing their distance, they’ve learned they’ve got to maintain strength by building muscle and they understand rest. This means avoiding injury altogether, or avoiding running through an injury. Those who are running late in life have been playing the long game for years. (But also, as stated earlier — genetics.)
How hard can I honestly run before my knees turn to bone meal?
That’s a good question for your genes, as well as your past self: As in, have you had knee injuries before? But apart from those factors, the answer to this question depends on how you run, and what you’re doing when you’re not running. What kind of surfaces are you running on? How are your shoes? Are you resting properly between running, and taking time off to recover from little injuries? Are you strengthening your muscles when you’re not running?
If you’re doing all this, with a bit of luck you too can be running an average of six miles a day in middle age, or 2,200 miles every year. Ficke, with his amazing running career in which he’s run dozens of ultra marathons (when he’s not busy being a surgeon and teaching surgery), is living proof of that.
Adam Elder
Adam Elder is a writer in San Diego. He's also written for Esquire and WIRED magazines, VICE, The New York Times, The Wall Street Journal, The Guardian, newyorker.com and elsewhere.
