ABSTRACT: We鈥檙e always looking for excuses not to run. Sure, it鈥檚 one of the simplest, cheapest, and most effective forms of exercise out there, but for many of us, running equals suffering. There鈥檚 no way around it: It sure as hell hurts. So we鈥檒l run with any excuse we can鈥攏o matter how pathetic鈥攖o stay on the couch. My personal go-to: Running is bad for the knees. In fact, it鈥檚 plainly irresponsible to tie up my Asics laces. But do I have a leg to stand on?
The Explainer
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鈬 Are Sports Supplements Killing Us?
HYPOTHESIS: We may have been born to run, but we鈥檝e evolved to be couch-bound; running wrecks the knees.
METHODS: A study in the journal tracked 74,752 runners over 7.1 years and 14,625 walkers over 5.7 years looking at the number of hip replacements and cases of osteoarthritis in each group.
RESULTS: The runners had fewer cases of osteoarthritis and needed fewer hip replacements than the walkers. Regardless of their mileage, runners were at roughly half the risk for osteoarthritis and hip replacements than walkers who expended equal amounts of energy (). Surprisingly, other forms of exercise were more damaging then either running or walking.
DISCUSSION: Old myths die hard, especially when people are looking for excuses. Still, how can running have the exact opposite effect as what we had expected? 鈥淎 lot of people think of exercise in sort of the automobile engine model where you tend to wear out the bearings when you use them more and more,鈥 says Paul Williams, Ph.D., an epidemiologist at the Lawrence Berkley Laboratory in Berkeley, California . 鈥淭he difference with the body is that it鈥檚 successful because it compensates for the stresses.鈥
While sports injuries do raise your risk of developing osteoarthritis and studies examining Olympic-class athletes鈥攚ho are often injury-prone鈥攕how high rates of the disease, the reality is different for nearly everyone else (in his 90,000-person sample, very few people fit this criteria, Williams says). Animal models show that exercise promotes cartilage thickening and protects its stretchy properties, according to Williams. In other words, instead of wearing down your bearings, running may grease them. That鈥檚 key, because cartilage thinning and the loss of elasticity are both prominent causes of osteoarthritis.
But things are a bit more complicated. Running may have special protective properties, but about half of the effect comes from weight loss, Williams says. 鈥淚f you were lean by other means would you still have this protective effect? Yes, but we still have the additional protective effect of whatever exercise is doing鈥 to reduce you risk of osteoarthritis. On average, your risk for the disease jumps five percent for every point-increase in your BMI. Surprisingly, the reason why is actually not well understood, he says. But researchers know the 鈥減hysical strain of carrying your weight around all the time鈥 likely stresses your joints and that obesity causes a cascade of negative effects in your body. Some of those鈥攍ike inflammation鈥攍ikely take a toll on your joints, Williams says.
While all physical activity should theoretically provide some protection for your joints, Williams says he was surprised to find that forms of exercise other than running and walking actually boost your risk of osteoarthritis. In fact, people who were most active in activities other than running were at a 21 percent greater risk for osteoarthritis and 99 percent increased risk for hip replacement compared to those who exercised the least.
What makes running and walking safe but going to the gym damaging? It comes down to how you use your knees, and we can take a clue from occupations like carpet-laying, Williams says. The deep knee bending is a known risk factor for osteoarthritis. The problem: When you go to the gym, you鈥檙e probably repeating some of those same moves. However, when you鈥檙e running, your knees aren鈥檛 bending to that same degree. And it鈥檚 a far more continuous activity鈥攚ithout potentially damaging long pauses or stops and starts鈥攖han doing an indoor exercise class, Williams adds.
The one bit of bad news: Your risk of developing osteoarthritis jumps 3.9 percent per year for guys and 6.1 percent per year for women. And the longer you鈥檝e been running, the more at risk you are. But even then, 鈥渢he benefits of running outweigh the risks for 70 years,鈥 Williams says.
CONCLUSION: We鈥檙e down another excuse. Injury-free running is not bad for our knees.