If you're a runner, especially one who's been running a while, you've undoubtedly heard, "Why do you do that to your body? Doesn't it hurt your joints or knees?" This often comes from someone eating a double-bacon cheese burger, fries, and a Coke. It's hard not to reply back with a similar set of questions, but replacing "knees" with "heart."
I guess it's not too bizarre of an assumption that running could be bad for your joints, after all your knees do absorb about 8 times your body weight with each stride when running. For me that's 1,104lbs, and I'm a little dude. That sounds like a lot of force/weight, and it is, but you know what, the body is an amazing machine. The human body was actually designed to run and Mother Nature crafted some pretty amazing shock-absorbing mechanisms to handle that force.
It's been fairly common thought that regular running during adolescence as well as involvement in other sports that impact the joints at an early age may lead to osteoarthritis in adulthood. One research study back in the 90s seemed to support this thought. Basically is showed that of the 5000 women involved in the study, the ones who were involved in heavy physical sports as teens or were involved in weight-bearing exercise in middle age had a higher risk of developing osteoarthritis of the hip. Well, that was one study.
Today's research is showing the opposite, especially in respects to running. A long-term study out of Standford shows that there's no connection between running and arthritis. Actually the study shoes that running and other "regular vigorous exercise" may even protect the joints in later life. The study followed a group comprised of 1,000 people (runners and non-runners). None of the participants had arthritis at the beginning of the study. Many of them had arthritis by the end of the study. Interesting finding was that the runners' joints were no more or less healthy than the non-runners in the group. This was true for even the really high-mileage runners in the group (averaging over 2,000 miles a year). Another great finding from the research was that the runners tended to be in better health and they had a 39% lower rate of mortality than the non-runners.
There's other research coming in with similar findings. Together all the research seems to be saying that osteoarthritis is mainly determined by genes and other things like obesity. Research shows that obese individuals are four times more likely to to get arthritis than leaner individuals.
Going back that what I said about Mother Nature.... James Fries (the leader of the Standford research) says, "Normally functioning joints can withstand and actually flourish under a lot of wear," In a recent Time article, he explains that healthy joints depend on movement because cartilage depends on the "pumping action generated by movement to get its regular dose of oxygen and nutrients. When you bear weight, [the joint] squishes out fluid, and when you release weight, it sucks in fluid." This is why daily exercise (including running) is good for keeping that cartilage healthy. Obese individuals may have an increased risk of arthritis because the added weight they're carrying is putting constant stress on their joints while at the same time, they're probably not very active so their joint cartilage isn't benefiting from that"squish factor."
The key is to avoid overuse injuries. Even though your joints like the exercise, you still need to incorporate rest into your running/exercise program. Your body needs time to regenerate and repair which in return builds up your body making it stronger. Another way to avoid overuse injuries such as stress fractures is to increase muscular strength. "Increasing muscular strength" is a phrase that often scares runners because they think it means adding bulk. However, you can increase muscular strength as well as muscular endurance without bulking up. If you focus on lighter weights and more reps, you're not going to end up with the "Arnold look."
Think about it. If you strengthen the muscles not only is this going to protect/support your bones, it's also going to help protect those joints. Your calve muscles are natural shock absorbers for your lower body. You don't need "boulder calves", but if you increase your calf strength, you'll increase their shock-absorbing capabilities at the same time. (Side Note: once during a marathon, my calves blew out. As a result, I ended up with a stress fracture in my heel. I now add calf-strengthening exercises to my weekly routine.) A simple way to to this is by doing body-weight calf-raises or standing calf-raises holding light dumbbells.
Your glutes and hamstrings are also great running muscles not only for power and speed, but for shock absorption as well. The ball-bridge-burnout and dead lifts (using moderate weights) are great ways to strengthen those muscles.
Hamstring Exercises with a Stability Ball -- powered by eHow.com
So the next time, someone says, "You know, running's bad for your joints." Be sure to reply, "Nope, actually it's exactly what the doctor ordered!"