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I have been running consistently for nearly 17 years. Over that 17 years, I've had one major injury and that required surgery (a labral tear in my right hip). I've had minor things pop up, like a mild case of runner's knee, a hamstring strain, and temporary aches/pains. I've put thousands of miles on my legs and I don't plan to stop anytime soon. A question I'm often asked is, "Isn't running bad for your knees?" I'm not a doctor or a physical therapist. I have an outdated personal training certification and anecdotal experience. But here is my take on the knees question.
Things that will hurt your knees:
1. Bad form: Good running form is fairly nuanced. The best way to examine your form is to take a video of yourself running from the front, back, and side. You should land on your midfoot, your strides should be quick and efficient, your posture straight, and your arms at a 90-degree angle. Watch this video for more details on good running form.
2. Bad Footwear: Finding the proper shoe for your gait and foot is important not only for injury prevention but for comfort. Consider factors like cushion, width, heel height, and shoe weight. If you're able, visit your local running store to have your feet measured and try on shoes before you buy them. I personally wear Altra shoes because I have wide feet and prefer a zero drop heel.
3. Doing Too Much Too Soon: A cardinal sin of new runners is increasing mileage or intensity too quickly. The rule of thumb is to increase your weekly running mileage by 10-15% every week, with periodic "down" weeks to ensure your body can recover. Jack Daniels, a famous running coach, believed that it takes roughly six weeks for the body to adapt to a new training load. Theoretically, after six weeks, you can increase your volume/intensity and reap maximum benefits while keeping your risk for injury low.
4. Neglecting Strength Training: I grew to love strength training because I learned first hand that strengthening my body keeps me healthy and injury-free. Every time I've seen a physical therapist, they have nailed my pain down to one of a few things: a weak core, weak glutes, or an imbalance in my glute/quad/hamstring strength. When I had a mild case of runner's knee, I hit the gym to strengthen my core, glutes, and hamstrings. A few weeks later, I was healthy and running again. When I strained my hamstring, my physical therapist identified tight hips and an imbalance in my quads and hamstrings. Now, I use sandbags to strength train twice a week and I've never been healthier. A few great strength training resources include the Runner's World Guide to Strength Training, this guide from Outside Online, Ben Beeler Fitness, or this free 16-week guide. My personal strength training lessons are: focus on your weaknesses/things you're not good at; core strength is important for everything; don't neglect the upper body; mix up your routine and gradually increase your training load; you're not going to get bulky from lifting heavy weights.
5. Not Resting: This is another cardinal sin of old and new runners. It's easy to get caught up in a training plan and not let your body rest but you'll suffer in the long run. I run six days a week, reserving at least one day for rest or light movement, usually a walk or yoga. One of my coaches used to say that it's better to be slightly undertrained than overtrained and injured. Every time I've sustained a small or large injury, I wasn't resting enough. I thought that more was better and ended up injured, so learn from my mistakes. Read more about how to take advantage of rest days here.
To ensure your knees, and the rest of your body, is healthy, strength training is a great place to start. Buy good shoes, gradually increase your intensity, inspect your running form, and you should be set up for success. But if you're still convinced that running will damage your knees, I'd suggest doing a reading some studies or maybe taking up a sport like swimming. One multi-year study of almost 75,000 runners published in July 2013 found that running does not increase the risk of developing osteoarthritis. In fact, runners in the study were found to be in less jeopardy of developing arthritis than their non-active counterparts. Another study, published in September 2013, showed that, while the impact from running is high, runners' feet strike the ground less frequently and more briefly than if they were walking, so running and walking put the same degree of stress on the knees.