The body is an all-terrain vehicle. We cannot run on concrete for long without consequences. In the case of running, the definition of insanity is doing the same thing over and over and expecting to get away with it!1 Although most runners believe that the rigidity of concrete is the main problem, it may be that the continuity of the surface is just as bad or worse.
Unfortunately, most recreational runners are running on sidewalks. Any sunny morning, you can see hundreds of them on the seawall in downtown Vancouver. They never touch the grass or the sand. They have succumbed to the illusion that a hard, constant surface is the path of least resistance. But on an unvarying surface, your body is subjected to exactly the same forces with every strike of the foot. Not only is the stress of impact exaggerated by the hard surface, but it is also repeated excessively because the mechanics of every step are exactly the same.
Worse still, the body is given no chance to adapt to other stresses. At best, same-surface and hard-surface runners become strong in one way, but weak in all the others — and therefore vulnerable to injury.
A classic runner’s injury, for instance, is a repetitive strain injury called iliotibial band syndrome. One possible cause of this condition is muscle imbalance: a relative weakness of the gluteus medius and minimus. (This is a controversial theory, and I don’t quite buy it.2) These muscles are lateral stabilizers; they control side-to-side movement of the hips. On a flat surface, they aren’t needed much — it’s easy to stay upright on a flat surface. They don’t exactly atrophy, but the other leg muscles get disproportionately stronger. When you see people running sideways, this is partly what they are trying to prevent. It’s a good idea, but it’s futile unless they do at least half the run that way.
Unyielding concrete and asphalt pose a number of difficulties for the runner’s anatomy, but the most obvious is probably the triple threat of the three main kinds of shin splints: (1) medial tibial stress syndrome, (2) compartment syndrome, and (3) stress fractures. (The term “shin splints” is not diagnostically meaningful in itself: it just means “shin pain.”) All three can be show-stoppers for serious runners. Compartment syndrome can even be dangerous, which is why all runners need to know that you should never try to “run through” worsening shin pain.3 All three are caused and/or aggravated to some degree by running on a hard surface.
Intriguingly, the evidence shows very clearly that the overall degree of impact is not actually a significant risk factor, while the speed with which you hit the pavement — the loading rate — is only a modest factor.4 (This might seem rather counter-intuitive at first, but it’s not so strange when you consider that there are undoubtedly many, many other variables. For a more complete discussion of the evidence about impact, see the shin splints tutorial.) Nevertheless, it’s a factor we can do something about, and the surface you’re running on is a big determinant of loading rate: it’s obviously more jarring to run on harder surfaces.
Human anatomy is well designed for shock absorption, but there are limits, and highly repetitive pounding on a hard surface can simply crack the tibia (stress fracture). The tibialis anterior and other shin muscles have the job of preventing the foot from “slapping” — if something didn’t hold the foot up a little bit after heel-strike, the forefoot would slap down loudly and awkwardly. On a hard surface, the transition from heel strike is particularly intense. It’s the tibialis anterior muscle that controls it, with strong and well-timed eccentric contractions that ease the foot down, somewhat like the biceps lowering a barbell — except it’s more like catching a barbell that’s being dropped from five feet up … hundreds of times in a row. You see the problem.
Eccentric contractions are a bit strange. How, exactly, does a muscle both contract and lengthen at the same time? There is obviously a need to lengthen muscle while still bearing a load, or you could never put anything down. But, believe it or not, despite a working theory about the chemistry of muscle contraction that’s been around for decades, no one really knows how eccentric contractions actually work.5 About all we do know is that they tend to cause much greater delayed onset (post-exercise) muscle soreness. Presumably, this also means that they are harder on the muscle.
When the tibialis anterior has been sufficiently irritated, it tends to develop severe myofascial trigger points and swell — and by an accident of anatomy, its muscle sheath is a bit small, creating a dangerous situation. Without room to swell, it only gets more irritated, and tries to swell more … you get the picture. This is a physiological design flaw.
The same forces that can put the tibialis anterior in this sorry state may also start to simply rip lower leg muscles off the bone, damaging the connective tissue wrapping around the bone, and/or the underlying bone (medial tibial stress syndrome). Ouch.
So don’t run on hard surfaces, kids — not if you can possibly avoid it!
Yet another common runner’s injury is probably bothered by hard surfaces: patellofemoral syndrome. Unlike with shin splints, there’s no superficially obvious problem with impact forces. The actual problem isn’t hard to understand, though: the less give there is in the road, the more the legs have to do the job of shock absorption. The body does this well, but it means that you are using the joints more — a tiny little bit more flex with every step. It adds up!
When you step off the road, or even a slightly softer road, there’s just a little bit less for the joints to do.
The problem with patellofemoral pain is usually tissue fatigue around or near the joint between the patella and the femur. This joint is always working hard. Pressures under the kneecap are spectacular even when nothing spectacular is going on: when the knee is flexed, it’s naturally cinched up against the front of the knee so hard that you literally couldn’t get it off with a crowbar (the bone before you could move it. It’s amazing that the tissue mostly handles these pressures. But of course if we chronically demand maximum performance…
Sandpaper your arches until they are raw and then go for a barefoot run: that’s what plantar fasciitis feels like. This RSI involves fatigue of the connective tissues of the arch, the plantar fascia, which are part of the system that makes the arch springy. The less give there is in the running surface, the more the arch has to do its thing. The less variation there is in the running surface, the more exactly the same the loading on the plantar fascia with every step.
There’s no direct evidence this is actually a problem, unfortunately. It’s mostly just a reasonable theory. However, there is some decent indirect evidence. For instance, we know that plantar fasciitis is prevalent in manufacturing, where workers usually work on concrete, and “work stations that decrease the percentage of time walking or standing on hard surfaces may lower the risk for plantar fasciitis.” Chances are good that’s true for runners too, because they use hard surfaces even more intensely.
We probably don’t need to overthink this one, though. Consider the obvious: people with plantar fasciitis really don’t like to stand on pavement, and find shoes with good arch support to be a great relief.
The solution to most running problems is to get off the concrete. Even trail running (chip trails and other groomed trails) is not adequate — it may be soft, but it is still same-surface running. We have evolved miraculously complex reflexes and musculature that can keep us upright on virtually any surface, even shifting surfaces like the deck of a ship. To develop and maintain a well-rounded fitness, all of those reflexes and musculature need to be constantly stimulated and challenged!
Ideally, everyone should do true trail running, or cross-country running. Your run should be on soft, constantly changing and unstable surfaces. For instance, I live in downtown Vancouver, which is runner’s Heaven: miles of scenic seawall running. The seawall itself is paved. But for most of its length, you can stay off of it, and run on beaches or grass, hop over logs and benches, go up and down hills, scramble over rocks. This is perfect!
Alas, most people don’t have the option of running on the beach. The solution is what I call “urban cross-country.” The key to urban cross-country is creativity: do anything you can to vary your running surface, and to get off the concrete every chance you get. Put parks on your route whenever possible. If it’s a small one, run around it on the grass five times before continuing. No park? Run on people’s lawns! The sidewalk is not your path: everything else is. Look for stairs and steep hills, and put them in your route. Run with one foot on the curb and one foot off for a block.
Getting the idea? Just do anything you can think of to keep changing the stresses on your body. Not only will this prevent injury, but it will make you much stronger.
Prevents injury? Really? A reader comments: “When people who are used to running on the sidewalk go all-terrain, they tend to sprain their ankles and knees because they have not the muscle or reaction training required for cross country!”
That’s a fair point. All-terrain running is certainly a risk factor for iliotibial band syndrome, for instance, because that condition is infamously irritated by running down hills.
In general, however, I think most runners are fairly safe because they rarely tackle cross-country with excessive zeal. It’s hard to wean people off the concrete at all — that “path of least resistance” is seductive. Running on concrete is part of the culture of running, and some serious runners have even told me, “I have to run on concrete, because that’s where you run races.” Fair enough. But that doesn’t mean it’s good for you! Obviously you should train on concrete if you intend to compete on concrete. However, I will continue to urge people to practice moderation and to subject themselves to a variety of stresses as a better formula for overall fitness.
Roger Davies, running researcher and medal winner in the 800-metre run at the 2005 World Masters Games in Spain, recommends a running technique in a similar spirit called “natural posture” running. He believes that adult runners need to imitate the running style of children, leaning forward with their arms swinging and feet flat. “Your body has to get back to its natural self,” Davies says. “Loose shoulders, loose hips. A lot of us are very tight.”6
The loss of well-rounded fitness in our society is in part the inspiration for the “core stability” exercising trend, and explains the burgeoning popularity of Pilates and Yoga. We probably lose core stability without a variety of exercise. While core stability exercise may have its place in our lives, core stability training for its own sake would probably be much less necessary if only we would walk and run on the sand or the grass more often.
I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.
— Added a new section about plantar fasciitis.
This study of studies — a meta review — tried to figure out if stress fractures are connected to ground reaction forces (the force of your strike) or with loading rates (how fast the force is applied, i.e. more slowly or more jarring). The authors found that the force you are striking with has no connection with stress fractures, but the “the vertical loading rate was found to be significantly different between the two groups.” So, according to this science, it’s not how hard you hit the ground, but how fast you hit it. However, science was also a little unclear on something important: the correlation identified is statistically “significant,” but the size of the correlation is probably not large (impressive numbers would be given in the abstract). So it’s how fast you hit the ground, but probably only to a modest degree. Presumably there are quite a few variables involved, which reduces the importance of even the most seemingly obvious risk factors.BACK TO TEXT