Does running actually destroy your knees? 🦵
The Portland Marathon rolled through town last weekend, and if just the thought of 15,000 runners hitting the pavement made your legs sore, you're not alone. For years, we've been told running is murder on your joints, but it's often the well-intended advice coming from someone who has never once jogged to catch a bus 🚌
They mean well. They're also working from a script that the research retired years ago.
This newsletter opens the can of worms on every question you didn't even know you had about what running means for your body 🪱
The warning has it backwards 🙃
A 2026 review pulling together the recent evidence on running and knee arthritis found something that reorganizes the whole conversation: the risk follows a U-shaped curve. At one end sit the people who barely move, at the other end sit the extreme high-mileage racers, and down in the comfortable valley in the middle sit recreational runners — with, get this, the lowest rate of knee and hip arthritis of anyone.
The numbers are almost comical. Recreational runners develop hip or knee arthritis at a rate of about 3.5 percent. Sedentary people — where the ones who skipped running specifically to protect their joints land — come in around 10 percent. So avoiding running to save your knees turns out to be roughly three times worse for your knees than just running. It's like never using a cast-iron pan so it stays nice, and discovering it's rusted into a modern art sculpture 🍳
Why movement is the thing cartilage wants
Cartilage doesn't have its own blood supply. It feeds and maintains itself through pressure — the rhythmic load of being compressed and released is the cue for it to stay healthy and rebuild, a process with the delightfully industrial name of mechanotransduction. Running, in sane amounts, is that cue on repeat. Take it away entirely and cartilage slowly deteriorates from disuse, which is a rough outcome for a tissue you'd like to keep.
It's also why "rest it completely" is often the worst prescription for a cranky joint, and why the loaded carries on the turf and the squats in the cage are doing your knees a favor rather than a disservice 🤝
But what about the marathon people?
Although sometimes we feel like an elite athlete for walking to the gym and back, for the sake of clarity, joint risk typically only climbs at truly extreme, sustained volume — north of 57 miles per week, held for years, where you'll find professional and international-level competitors. That's the far tip of the curve, and almost nobody lives there.
For scale: a half marathon every weekend wouldn't put you close. Training for and running a full marathon wouldn't either. You'd have to log the equivalent of about two marathons' worth of mileage every week, year after year, to reach the zone where the research starts raising an eyebrow. Last weekend's marathoners aren't grinding their joints to dust — by the evidence, they're parked in the protective dip of the curve. The race was never the threat. Running a hundred of them a year would be, and also a medical curiosity 🤔
Pavement or dirt?
If you're choosing where to put those miles, the two surfaces trade one risk for another rather than one simply winning. Trail running tends to come with fewer overuse injuries — the ground has more give, and the constantly shifting terrain means your foot lands a little differently every stride instead of hammering the identical spot a few thousand times in a row. The catch is that all that uneven footing raises the odds of the sudden stuff: rolled ankles, trips, the occasional surprise meeting with a tree root.
And the "soft ground saves your joints" idea is a bit oversold. A study that measured the actual force traveling up through runners' legs across different surfaces found no meaningful difference in peak impact — because runners unconsciously adjust leg and knee stiffness to match what they're landing on, so the force reaching the joint stays more similar than it feels underfoot. The softness might make the force arrive slightly more gradually, but a good chunk of the trail advantage is the variety of foot strike, not the cushioning. None of which means one is correct and the other is wrong — just that if your ankles are dicey, the predictable sidewalk has its merits, and if the repetitive pounding is what nags you, the trail might treat you kinder 😌
A bump in the curve
As much as we'd like to say we're all carrying the same risk factors, every body is unique, and each comes with its own liabilities 🥲 To be clear, the U-curve is real, and it applies to you too — being older, heavier, or carrying an old knee injury doesn't bump you off it, it just raises the whole curve a notch. The protective dip is still a dip; it's just drawn a little higher on the graph.
But when researchers looked at what actually moves a runner's risk for osteoarthritis, marathons logged and years on the road weren't the culprits. Age, body weight, and a history of serious joint injury were the indicators. So the takeaway doesn't flip — running still beats sitting for nearly everyone — but if you've got those factors in play, you've got more reason to build gradually, add strength work, and get a read on your specific joints from someone who can see them.
Genetics get a vote too — family history accounts for a meaningful share of knee arthritis, which is partly why one person can run for thirty years pain-free while another's knees complain early despite doing everything right. If you've got a banged-up joint in your history or a doctor who's already flagged your knees, the move isn't to swear off running — it's to build gradually, keep the mileage sensible, add strength work to support the joint, and loop in a professional who knows your specific situation rather than taking a newsletter's word for it 🤓
The question every lifter is now asking 💪
If your real love is the weight room, there's a different worry lurking: does all this running torch the muscle you've been building? Mostly, no. The big reviews — including a 43-study analysis — find that mixing cardio and lifting doesn't meaningfully shrink your overall muscle size or max strength, as long as you program it with a shred of intention.
The catch is that running picks more of a fight than other cardio. All that pounding comes with eccentric muscle damage your legs then have to spend recovery on, and the same analysis found running slightly dents muscle fiber growth where cycling doesn't — a small effect, but a real one, and the reason the bike is the friendlier choice when size is the priority.
The interference also lands harder on experienced lifters, which sounds backwards until you think about it. A beginner improves at nearly everything at once because every stimulus is new, so a little competition between running and lifting barely shows up. A seasoned lifter is already scraping for small gains near the top of their ability, so the same slice of interference eats a bigger share of what little progress is left to win. The further along you are, the more it costs you.
Where this actually bites is timing. Lifting keeps the muscle-building signal elevated for a day or more afterward, and hard endurance work triggers a competing signal that suppresses it — so stacking a tough run and a heavy lift close together blunts the payoff from both. The research consistently points the same way: give them room. A full day between your hardest run and your hardest lift is ideal, and if they have to share a day, put several hours between them. Running on legs still wrecked from yesterday's squats isn't doing either session any favors.
None of this means running undoes your lifting. It means you don't want more than a few hard endurance sessions crammed into the week if muscle is the goal, you don't want to run yourself into the ground right before leg day, and if you'd like cardio that stays entirely out of the way, the bike and the assault bikes pick almost no fight at all. Space the hard stuff out and the conflict mostly disappears 🚲
The great fat-melter
A note, since running gets marketed as the great fat-melter: your metabolism is annoyingly good at defending its weight. Burn a pile of calories on a long run and the body tends to answer by bumping your appetite up and your incidental movement down, clawing back a chunk of what you spent before the sun even sets. Running is spectacular for your heart, your head, your joints, and how long you'll be around to enjoy them — it's just not the one-way ticket to a new body composition the apps imply. For that, the classic answer still wins: pair it with lifting and mind what's on your plate. The same lesson we keep bumping into from every direction, now in running shoes 👟
So if last weekend's race left you itching to lace up, the research is squarely on your side, knees and all. Start where you are, build gradually, and let the folks warning you about your joints keep dispensing their wisdom from the sideline. Statistically, they're the ones who should be nervous 😅
See you on the road (or at least the treadmill),
Your West Coast Fitness Family
PS: A note for our community: the details for David's Celebration of Life have been updated. It will be held Saturday, October 17th from 12 to 2 PM at the St. Johns Community Center. The gym will be closed during those hours so our staff can attend and pay their respects. We hope those who knew him can be there 🤍
