As many of you know, I am a graduate student in engineering where my research is focused on osteoarthritis of the knee. It’s always fun to talk about my research with other people, especially family and friends. Many of them don’t understand how I can study something like arthritis and still continue to run. I remember when my cousin’s former boss once said to me: “You better enjoy it now, because by the time you’re 50, you won’t be able to run anymore.” I can’t tell you the number of people who tell me that I’m going to wear my knees out with as much running as I do.
Of course, I want to make sure this isn’t true. I want to continue running until I’m 50. Scratch that, I want to run for fifty years after I turn 50… if I can. So I do certain exercises. I strength train, I stretch, I pay attention to my form. I buy new shoes every 400miles, and I try not to overdo it. But should I really be worried about wearing my knees out?
A lot of research has been brought to the forefront recently, and that’s what I want to discuss today. Adam brought this article by Gretchen Reynolds from the New York Times to my attention this afternoon. The article, “Can Running Actually Help Your Knees?,” debunks a few myths related to the sport of running. Everyone knows being active is good for you, right? Well, it gets tricky when you start to think about what kind of activities you should participate in. Are you trying to lose weight? Reduce stress? Make sure your joints stay healthy? Avoid injury? I suppose I could discuss how biking is dangerous, because it puts you at a risk of getting hit by a car or crashing into a ditch, but all external factors aside, let’s talk about health benefits of an active lifestyle, particularly: the lifestyle of a runner.
Think of knee joint health as one big cycle. We stay active, avoid getting injured, and we stay healthy. We build strong muscles, strong bones, strong cardiovascular systems. Our mood is lifted, because exercise releases endorphins. Maybe we eat better, incorporate more fruits and vegetables because we want to fuel our bodies the right way. If something happens, though, and we get injured, then what happens to the cycle? Our activity levels decrease, our mood might go south. We lose some of the strength we had worked so hard to built up. Joint injury is bad in this way, for sure. But it could also be worse in the long run. After an injury, sometimes we turn into a couch potato, and this ramps up the amount of time we’re sitting around doing nothing. We’re not loading our joints, we slow down and reduce the amount of time we’re moving around. And that’s not what our joints were meant to do.
In my research, I have read dozens of articles discussing the benefit of knee movement on joint health. Some of you may have even experienced these therapies in real life. For example, studies implementing animals models have been used to illustrate the anti-inflammatory effect of continuous passive motion (CPM) on knee joint health (Feretti et al 2005; Kim et al 1995). These devices are now used clinically for post-surgical rehabilitation for people with total knee replacements. That little device they strap your knee into after surgery and it goes back and forth, bending and straightening your leg? You betcha that’s a CPM device. But why wait until after a total knee replacement to start moving your knees? The cartilage is gone by then, because the doctor removed it. We have to do something now.
Many have suggested the benefits of bicycling for knee joint health. The key words: Low Impact! But if biking is so good on your knees because it’s low impact, then running, man- that’s got to be bad. All that pounding on the pavement, over and over again. Or is it?
Before we get into that discussion, I want to take some time and talk about the knee. It’s not just two bones strapped together by muscle and ligaments. There’s a whole lot of stuff going on (see below). The thigh bone, also known as the femur, makes a hinge joint with the tibia (shin bone). There are two bones in the lower half of the leg, but only the tibia, femur, and patella (knee cap) are what really make the knee articulate. The ends of the tibia and femur, as well as the internal side of the patella, are lined with cartilage, a smooth, somewhat compressible tissue that is basically like a lubricated rubber liner for our knee. Atop the tibia rest two C-shaped disks, the menisci, that are attached to the tibia only by their attachment sites (the tips of the C’s). These are the “shock absorbers” of the knee, and as the knee moves, the menisci also move. The menisci are also attached to the outer edge of the synovium as well as the medial collateral ligament. There are other ligaments, too, like the anterior cruciate (ACL; not shown), which prevent the knee from misaligning (the ACL prevents the tibia from moving forward with respect to the femur).
So back to the topic at hand. In the NYT’s article, Reynolds discusses how our knee cartilage is made to be loaded. True, many researchers have observed a positive influence of loading- in sheer, especially- on the cartilage and meniscus. The chondroprotective nature of the meniscus (in other words, the menisci’s ability to protect the underlying cartilage), has also been shown to be influenced by loading, both good and bad. Sure, the meniscus can tear. So can ligaments. And when that happens, it puts unusual loads on the remaining intact tissues that can cause malignment, cartilage damage, and pain. But there is also a protective influence of loading on the health of the chondrocytes and fibrochondrocytes, the cells that make up the cartilage and meniscus, respectively. We’ve shown in our lab that the absence and excess of loading on the meniscus can lead to increased levels of matrix degrading molecules which weaken the material (Gupta et al 2008; Zielinska et al 2009). Likewise, we’ve shown that normal strain levels in the meniscus can lead to an anabolic response, promoting the tissue to get stronger by expressing genes for collagen, the molecule that provides stiffness in these skeletal tissues. I’m sure you’ve heard that “use it or lose it” saying, right? There are many researchers that believe if we don’t use our cartilage, it will essentially just go away- degrade, deterioriate- and when that happens, we’re in for a whole slew of problems.
In her article, Reynolds brings up a lot of very important points:
- Running, walking, and other forms of cyclic motion of the knee are actually good for your knee joint health
- There is little evidence that suggests running leads to knee joint degeneration
- Previous knee injuries are strong predictors of future arthritis.
So don’t live in fear! Run if you want to run. If you have had a joint injury, it’s good to talk to your doctor. Also, there are other factors, like weight, genetics, and immune disorders, that can play a role on the health of your joints. People who are obese are at a 50% higher likelihood to develop knee arthritis. Pretty scary…
So remember, talk to your doctor before starting anything new, but don’t be afraid of the “high impact” sport of running. Sti
ck to soft surfaces for the majority of your runs (this helps ‘save’ your legs in the respect that it makes them feel more fresh and responsive, as hard surfaces do not disippate impact energy as well as soft surfaces do). With the whole debate about whether to run on treadmills, trails, tracks, or sidewalks, I choose trails as much as I can. However, I spent a whole winter in 2007 training for a marathon on a treadmill, and I didn’t have any issues with my knees.
Get a good pair of shoes. Pay attention to your form, and try to strengthen your core and leg muscles. Strong, and balanced, leg muscles can help keep your knees in alignment and prevent injury to ligaments.
And remember, don’t over-do it. Some of the folks discussed in Stanford’s study on distance runners didn’t run back to back marathons every weekend- instead some would just run every few days, 90 or so minutes a week. The key is to stay active, keep the joints moving like they were meant to move.
Ah, it’s always nice to see reports encouraging people to continue to do what they love. For me, I’m just going to keep running.
References:Feretti, M., Srinivasan, A., Deschner, J., Gassner, R., Baliko, F., Piesco, N., Salter, R., and Agarwal, S. Anti-inflammatory effects of continuous passive motion on meniscal fibrocartilage. J Orth Res. 2005 Sep; 23(5):1165-71
Kim, HK, Kerr, RG., Cruz, TF., and Salter, RB. Effects of continuous passive motion and immobilization on synovitis and cartilage degradation in antigen induced arthritis. J Rheum. 1995 Sep;22(9):1714-21 Gupta, T., Zielinska, B., McHenry, J., Kadmiel, M., and Haut Donahue, T.L. IL-1 and iNOS gene expression and NO synthesis in the superior region of meniscal explants are dependent on the magnitude of compressive strains. OAC, 2008 Oct; 16(10):1213-9 Zielinska, B., Killian, M.L., Kadmiel, M., Nelsen, M., and Haut Donahue, T.L. Meniscal tissue response depends on level of dynamic compressive strain. OAC 2009 June; 17(6)754-60