Damn you injuries! (Photo credit: aaipodpics)
I’ve been part of an interesting email thread over the past few days. I’m not going to discuss any specifics, but the gist of the discussion has revolved around the question of whether shoes can cause running injuries.
The refrain lately in the running community has been that “form trumps footwear” when it comes to running injuries. That is, if you run with “good” form, you can manage to run in just about any pair of shoes. This sounds good and makes intuitive sense, but I think it’s a vast simplification of reality. The other common refrain is “running injures runners,” not their shoes. There is truth in this statement as well, but once again it’s an oversimplification.
So what is it that injures runners. My position is that it is the forces experienced during ground contact that cause running injuries. These forces include passive impact forces that occur at the moment of foot contact, and perhaps even more importantly, the active forces that the body experiences during the remainder of stance phase. If you don’t run, you don’t experience these forces, and thus you won’t suffer a typical running injury. I’m not going to argue at all with that – so yes, running does cause running injuries, but for a runner, not running is rarely a desirable option.
Among people who do run, are there factors that increase injury risk? Absolutely! Studies have looked at this question ad nauseum, and findings are mixed, but the 4 factors which repeatedly pop out as increasing risk include:
1. High mileage
2. Running to compete (i.e., racing and presumably speed training)
3. Limited running experience (i.e., new runners)
4. History of previous injury
These are factors that have been found in epidemiological studies comparing large groups of people. What do all four of these things have in common? Yes, they all involve running, but presumably the people who did not get injured in these studies were also runners. Why is it that these four factors in particular increase injury risk among runners? The answer is quite simple – they all either increase the amount of force applied to the body, or involve a poorer ability to manage the forces that are applied. Higher mileage and greater speed = more force and more wear and tear. New runners = tissues are less adapted to the force that is applied. History of injury = tissues are weakened and less capable of handling force application.
So how does this apply to shoes? When we run a lot of force is applied to the body. With every step we impact the ground with a force equivalent
to approximately 2 to 3 times body weight. To manage the applied forces during stance, our joints compress, our muscles stretch and contract, and our tendons and ligaments tug and rub on surrounding tissues. The average runner takes about 80 to 95 running steps per minute with each foot. Extrapolate that over a thirty-minute run and you are dealing with 2400 to 2850 contacts per foot, per half-hour. That’s a lot of stress to the body!
Now, some runners have no problem handling this amount of force application. They have good structure, good mechanics, good strength, stability and balance. They can run mile after mile without getting seriously hurt because their body works optimally to handle the forces applied. Other people have poor strength, stability, balance, etc. They might have imbalances in structure or muscle strength for example. They might have poor running mechanics. They might have an anatomical abnormality that makes it harder to manage particular types of force applied in particular ways. But here’s the key point – all of these things are force modifiers. They alter how much force is applied at what time during stance, and they influence where specifically forces are applied at the level of tissues. For example, someone with a weak gluteus medius on one side may have a hip instability that causes them to manage forces at the knee in a non-optimal way. This can lead to injury such as ITBS or patellofemoral pain syndrome.
I would group shoes in with all of these other factors as a force modifier because they do alter how forces are applied to the body. They can alter stability, joint torques and the timing and magnitude of force application. They can alter where specifically forces are applied – a good example of this is the increased burden placed on the calf muscles in low-drop shoes. Match the wrong pair of shoes with a runner who is otherwise healthy and the shoes themselves can alter force application in such a way as to precipitate an injury. This can go the other way too – move to less shoe or barefoot, and force application is modified in ways that can be either positive or negative. Which result occurs is highly individual and is dependent on all of the things discussed above (an individual’s inherent strength, stability, structure, etc. – I’d also include past history of shoe wear here). Sometimes runners can adapt to forces over a period of time and new shoe works out fine, sometimes they can’t and the only solution is to ditch the footwear and try something else.
Having myself run in probably more than 75 pairs of shoes over the past 5 years, I can confidently say that there are certain shoes that have caused me pain. My most recent example is the New Balance MT110 – the slanted sole causes my feet to evert excessively just standing in them, and I developed a very tender posterior tibial tendon after a long trail run in the shoes. Never had the pain in any other shoe. Might I have adapted with continued use? Perhaps, but why would I want to adapt to a shoe that causes me pain when there are equivalently built and priced options that don’t cause me trouble? Another example are the Vibram Fivefingers – I often get an ache under my second metatarsal after running long in them, never feel this in other shoes. I suspect it has to do with fit and a resulting reduction in ability of my toes to flex and share the load during take-off (not to mention that the lack of cushion probably increases focal load on the second met head). A third example – before I cut the forefoot band, the New Balance MT10 caused me wicked ITB pain on one side. Never happened in any other shoe, and pain went away after I cut the band. I could go on…
So my point here is that although form seems to be king these days, let’s not forget about footwear (and I haven’t even touched here on the fact that footwear can influence form). Let’s not give shoe makers a free pass to claim user error when a shoe causes a problem. Sometimes the shoe is at fault when a running injury pops up. It may not be all the time, it may not even be often, but to ignore our footwear when it comes to managing pain is misguided. Shoes matter!