Does running on concrete hurt your knees?

Running on hard surfaces can sometimes lead to more stress and result in injuries like inflation in the achilles tendon, shin splints and stress fractures in the small bones of the foot or ankle. Running on soft surfaces can lead to injuries, such as a twisted ankle or knee, due to the irregularities of the ground and the runner attempting to compensate for them.

To help runners determine which surface may be best for them, here are the pros and cons to different types of running surfaces.

Asphalt

Pros: Asphalt is typically soft and level making it one of the better running surfaces. It also puts less strain on the Achilles tendon.

Cons: Asphalt puts some strain on the body as it doesn’t absorb all of the shock that travels through a runner’s body. It can aggravate the shins more and can cause stress fractures.

Concrete

Pros: Concrete surfaces are smooth and regular. This will allow a runner to develop a rhythm.

Cons: Concrete is the least forgiving of running surfaces, according to Timothy Noakes, author of “Lore of Running.” When running on concrete, the ground doesn’t absorb any of the shock that travels through a runner’s feet, knees, hips and lower back. This can lead to an increased injury risk. Concrete should typically be avoided when possible.

Grass

Pros: Running on grass will likely cause little discomfort because it has a low impact. It will also make a runner’s legs work harder compared to running on a track, therefore creating small improvements in leg strength.

Cons: While not the worst running surface, grass will still cause a  25 percent greater shock to the body than running on asphalt, according to a study in “Human Movement Science.” It can also be uneven and slippery when wet.

Sand

Pros: Sand has a minimal force of impact on joints while running. It also makes legs work harder compared to running on a track.

Cons: Running on soft sand can increase the risk of an injury to the Achilles tendon. It can also lead to a twisted ankle or knee if the sand is unstable.  If sand is sloped, it may cause uneven stresses on the body.

Hard-surface running might be a risk factor for running injuries like patellofemoral pain, IT band syndrome, shin splints, and plantar fasciitis

The body is an all-terrain vehicle, born to run two million years before roads,1 and so maybe we suffer when we run for a long time on asphalt or concrete. Although running is an extremely healthy sport overall, and nowhere near as hard on the body as most people fear, running injuries are still common and frustrating and the risk factors for them remain mysterious. Could it be the roads? Is it insane to do exactly the same thing over and over again with your anatomy — the very same forces, step after step — and expect to get away with it?2 It seems almost obvious, but no one actually knows. Just as with running barefoot or minimally shod — a sort of mirror image of this topic — there’s a surprising lack of hard science about running on hard surfaces … and some of the scientific evidence we do have is surprising.

Although most runners fear the rigidity of concrete or ashpalt, the problem might actually be the continuity of the surface, the unrelenting same-ness of pavement. But there’s even less evidence about that possibility.

Important safety issue: for people with joints that may be unstable from previous injuries (e.g. ankle sprains), running on uneven or unstable surfaces (trails especially) may be the greater of evils. The evil-ness of roads is an unknown, but there’s no question that it’s all-too-easy to sprain an ankle on a trail run.

Citation badly needed! Are roads really risky?

It seems common-sensical that running on hard surfaces is risky. Surely harder surfaces involve more impact, more biomechanical stress, and therefore more injury? Unfortunately, like many “obvious” ideas, this one has a glaring citation needed problem. Is there any direct scientific evidence that running on hard surfaces is actually injurious? Has anyone ever gotten big groups of people to run for a long time on different surfaces, measuring injury rates in both groups (a prospective trial)? Incredibly, no: despite decades of running research, it’s still an untested idea (as of late 2022).3

So it’s not proven that hard-surface running is risky, but it’s not exactly a crazy idea either. It’s a reasonable hypothesis, and there are arguments and evidence both for and against it. First, the arguments against…

Hard surfaces are innocent! The case for the defense

Here are some of the clues and perspectives that cast doubt on the alleged “danger” of running on roads and sidewalks:

1. Runners’ joints are in great shape. A 2018 study showed that runners probably have half the rate of knee and hip arthritis than non-runners.4 This generally undermines the popular idea that running is “hard on the joints,” and suggests instead that it’s actually stimulating adaptation, making joints tougher. If true (and it almost certainly is) it undermines the obviousness of hard surfaces being problematic.
2. Humans have amazing shock absorption features. For instance, when we run onto a new surface, we adjust the spring in our step after one step — by adjusting our leg stiffness.5 We dynamically adjust our shock absorption, and we’re extremely good at it.6 Which suggests that surface hardness might not be a big deal.
3. “Impact forces” are not strongly associated with injuries. “The evidence of the link between injury and impact related factors is either just not there or far from compelling,” writes Craig Payne on RunResearchJunkie.com, summarizing a review of studies.7
4. Shoes don’t make much difference. If surface matters, then what we put between our feet and the surface probably matters too — a proxy surface — but no kind of shoe (or lack of shoe) has been clearly shown to make any important difference in injury rates. It was only in 2016 that we finally got good data on barefoot running compared to shod, and they were quite similar — different injuries, but the same overall injury rate.8
5. Ignore fear-mongering claims made without evidence. “Common sense” is often suspect, and Hitchen’s razor cuts deep here: “What can be asserted without evidence can be dismissed without evidence,” and probably should be dismissed if it discourages people from participation in what is clearly a healthy activity. In other words, until we actually know, let’s err on the side of not making people scared of a risk that may not exist. A positive attitude truly matters in rehab.9

What can be asserted without evidence can be dismissed without evidence.

Christopher Hitchens, paraphrasing the Latin proverb “Quod gratis asseritur, gratis negatur” (What is freely asserted is freely deserted), in a 2003 Slate article

Hard surfaces are guilty! The case for the prosecution

The science cited above is just about the only science that clearly casts doubt on the dangers of running on roads, none of it is actually direct evidence, and there are caveats and “yeah buts” galore.

1. Maybe trails are even better! Just because runners’ joints do surprisingly well doesn’t mean they wouldn’t be in even better shape with off-road running. While the evidence on arthritis can tell us that road running clearly isn’t wrecking people, it is simply mute on the difference between harder and softer surfaces. Injury and arthritis are not imaginary; although bodies thrive by adapting to manageable loads, they do struggle to adapt and fail if the load is excessive. For all we know, off-road running is the loading sweet spot for most runners.
2. Shock absorption isn’t “free.” We may be good at adjusting our gait for shock absorption, but that doesn’t mean that there are no costs or consequences.10 When I hike down a mountain, I’m sure my legs very cleverly do everything possible to compensate for the stresses of taking thousands of steep steps downwards, but steep descents are still holy hell on my knees, and adding extra protection in the form of walking poles definitely helps.11 Clearly there are limits to our ability to absorb shock, but we don’t know where that line is drawn. Why not let the surface do some of the shock absorbing for you? Speaking of that …
3. There’s evidence that springier surfaces are easier on bodies. We know that more spring in the surface means less spring and bending in the joints.12 Hips, knees and ankles all bend less when you walk or run on a springier surface. This is a highly plausible mechanism for increasing the rate of overuse injuries running on non-springy surfaces. And what could be less springier than pavement?
4. The impact evidence is just not direct enough. Studies showing a weak link between injuries and impact forces are the closest thing to relevant science, but they are nowhere near as relevant as actually comparing the results of running on different surfaces. They are “circumstantial evidence.” They cannot definitively answer the scientific question. Nevertheless, I will look at this evidence in more detail below.
5. Actually, barefoot running is a problem. The best evidence on barefoot running and injuries actually supports (or is consistent with) the original common-sense notion that impact is a problem and the cushioning of running shoes actually does meaningfully protect us from it.13
6. Erring on the side of caution is reasonable. Erring on the side of not worrying sounds great to me — I want to champion everyone’s peace of mind — but there’s an obvious rebuttal. In the absence of evidence, how about erring on the side of caution? It would be ridiculous to advise total abstinence from the road — that would be fear-mongering nonsense. But minimizing it? That just seems like a good use of the precautionary principle… based on a risk that’s plausible.

My conclusions on the risk question for now

The arguments in summary:

1. Road-runners’ joints are in surprisingly good shape, but maybe they’d be even better off on trails.
2. We adapt to surfaces deftly, but there are probably limits and consequences to shock absorption.
3. Studies show no clear association between impact forces and injury, but they are not the right studies to answer the real question here.
4. Different types of running shoes don’t seem to have anything to do with injury, but a lack of shoes does.
5. Although it’s nice to avoid fear-mongering about a risk that may not exist, a better-safe-than sorry policy is reasonable.

So the jury on this topic is definitely out, and it’s going to stay out for a long time. Having weighed all the arguments and evidence rather thoroughly, here is my opinion for now:

• Running on pavement is probably a bit risky, but much less risky than lots of other popular things, like basketball, baseball (crazy injury rates in those sports, believe it or not) and hungry bear poking. Everything’s relative!
• We should beware of fear-mongering, but it’s wise to gently apply the precautionary principle, and minimize hard surface running and explore the alternatives.

Impact and running injuries

The impact of running is measured in many ways. Loading rate is the main technical way of measuring how jarring a runners’ steps are: how fast load is applied to tissues. Peak acceleration at various anatomical landmarks is another. There’s a lot of research about impact, some of it concerning different surfaces, just a few of those specifically about the relationship between impact and injury. As of the end of 2016, there were only about 18 decent experiments, with too many differences between them to clearly interpret. A review of these by van der Worp et al concluded just a single thing with confidence: a history of stress fractures is associated with higher impact forces in running gait.14

That’s it. Every other kind of impact/injury connection is still a question mark. “Owing to the absence of prospective studies on other injury types” — the only kind of study that could actually prove that a higher loading rate causes an injury — “it is not possible to draw definite conclusions regarding their relation with loading rate.”

But where there is smoke there is fire! Of all running injuries, stress fractures seem the most obviously relevant to impact, and the evidence does support that assumption: the one established fact. Furthermore, there is a broad association between higher loading rates and runners with all kinds of injuries (no specific one).17 And that’s backed up by a good quality trial from just a little later in 2016: Davis et al found that “all impact-related variables were higher” in 250 women runners who got injured in a year after extensive gait analysis.18 Plus there’s the same implication from Altman 2016 (previously discussed).

So the common-sense idea that impact is injurious appears to have some scientific support.

There are flies in that ointment, of course. Most importantly, “impact” is not equivalent to “hard surface,” as you’ll see in the next section. The limited evidence at this late date in history is noteworthy. And there are some miscellaneous clues that suggest that impact is not straightforwardly injurious.

For instance, Zadpoor et al found that ground reaction forces (how hard you hit the ground) have no correlation with stress fractures, and loading rates (how fast you hit the ground) are only slightly correlated.19 That’s surprising for what seems like the most impact-related running injury. When van der Worp et al concluded that loading rate is associated with stress fractures, it’s probably not the whole story.

Maybe it’s because the stresses that fracture are not simple. The forces in normal running are mostly below the threshold at which we would expect them to cause stress fractures directly, but Milgrom et al demonstrated20 that there are much stronger forces involved in activities that involve greater shear strain,21 probably enough to cause fractures more directly/quickly. Thus it is runners who include a lot of stairs and jumps that are potentially at greater risk for stress fractures than just running, regardless of surfaces. This is just a good example of the thick layers of “it depends” obscuring the truth.

Maybe impact matters … but just matters quite a bit less than other factors, which makes it very hard to separate the impact-signal from the noise of bigger and badder causes. Because there are definitely other risk factors! A giant 2015 study of almost 1700 novice runners in a “Start to Run” program found that a lot of them got hurt (almost 11%), and of those that did get hurt were more likely to be older, heavier, have a history of previous musculoskeletal problems, and less prior running experience.22 Obviously this isn’t direct evidence about impact—it just emphasizes the presence of other “noisy” factors.

And that’s all I’ve got: I am not aware of any other evidence that impact is not an concern, just an absence of ample, conclusive evidence that it is.

And then there’s disconnect between “impact” and “surface.” If impact matters, that’s one thing. But do runners actually experience more impact on harder surfaces? This is really the key to this whole puzzle.

Is grass softer than pavement?

If you hit your head on it, there’s really no question, is there? But we must take nothing for granted! Some science does indeed support the obvious here: a straightforward 2012 experiment produced peak plantar pressures about 12% lower than hard surfaces.23 That’s not a huge difference, but I’m sure it adds up. After two hours of hiking with a 20kg pack, you’d probably be quite grateful for a 12% load lightening. And obviously not all grass is created equal.

Whether or not that 12% difference reduces injury risk is still anybody’s guess.

But hang on, this is way too straightforward for running science. There must be conflicting evidence. And there is: an excellent 2015 experiment by Fu et al found no difference at all in impact forces on any common running surface.24 Er, wut?

There was one key difference between this experiment and Tessutti 2012: their subjects weren’t running as fast. It’s possible, perhaps even likely, that a difference would have emerged at higher running speeds.

So Fu et al concluded that “these findings indicated that different running surfaces do not necessarily affect the peak plantar impact and, by implication, impact-related injuries in runners.” But their inference about injuries there is speculation: their findings cannot tell us anything about injury rates, and it’s equally reasonable to assume that, although runners can likely adapt their stride to cope with stiffer surfaces — which is neat — that adaptation probably also has a cost. There’s no such thing as a free lunch. That is, they may well reduce musculoskeletal stresses in the lower limb at the expense of greater stresses elsewhere — more evenly distributed, but they’re there somewhere.

Pavement seems more than 12% harder than grass

So Fu et al found no difference in lower limb impact forces on different surfaces whatsoever, and Tessutti et al found only a 12% difference between pavement concrete and grass. I don’t know about you, but the last time I hit my head on concrete, it felt a lot more than 12% harder than grass. Indeed it is.

Measuring rubber ball bounces is a good way of getting a nice apples-to-apples comparison of surface hardness without all the messy complexity of running biomechanics interfering. The point of this is that running biomechanics do interfere. Fu et al did this for us:

Both kinds of runners knee, IT band syndrome & patellofemoral pain, are probably aggravated by running on hard & even surfaces.

Yet another common runner’s injury may be 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, they may stop coping so well.

Plantar fasciitis on the road

Sandpaper your arches until they are raw and then go for a barefoot run: that’s what plantar fasciitis feels like. This common repetitive strain injury 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. And the less variation there is in the running surface, the more consistent the loading on the plantar fascia — the exact same forces with every step. While there’s no evidence that this is actually a problem, we do 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.”30 Chances are good that’s true for runners too, because they use hard surfaces even more intensely.

And a soft data point: people with plantar fasciitis really don’t like to stand on pavement, and find shoes with good arch support to be a great relief. These are classic features of the condition.

Alternatives to running on hard, even surfaces

Softer and uneven surfaces have their own risks of course — like tripping! and twisting ankles — but if you’re prone to recurrence of any of the injuries discussed above, you may prefer some new risks for a while.

Even chip trails and other groomed trails may not be enough of a departure from paved surfaces — it may be soft, but it’s 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, your run should be on soft, constantly changing, and unstable surfaces — but not so unstable that your risk of tripping and spraining spikes absurdly high, of course.

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, even scramble over rocks.

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.

But the devil is in the details. For instance, all-terrain running is probably a different kind of risk factor for iliotibial band syndrome specifically, because that condition is infamously irritated by running down hills.

Roger Davies and natural posture running

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.”31

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.

Impact reduction take-home points

• Stay off concrete as much as possible. Prefer tracks and treadmills for the bounciest of all options, the best at giving you some of your impact energy back and reducing the load on your biomechanical spring. (Grass, sand, and chip trails are much softer than pavement, but are more like running on foam: mushy, not springy.)

  I work just a couple blocks from a running track. I don’t usually walk there, because I’d far rather stick to tree-lined streets and parks. But if my plantar fasciitis flared up, for example, I’d absolutely make walking on that track part of my rehab regimen, because that surface is obviously springier than anything else I can walk on regularly. Not everyone has such a convenient option, of course, but it’s an instructive idea.

• Try sprung shoes. If you can’t run on a springier surface, then try shoes based on springs, like OESH Shoes.32 Failing that, at least keep your regular running shoes fresh — the EVA foam in the midsole breaks down,33 and the biomechanics of running do shift in response. It probably does not matter a lot, but there’s also no need to take the risk.34 Although we’ve established that any non-spring shock absorption (mostly foam) is fundamentally different and probably not very helpful, if I run on foam I at least want it to be fresh foam!

• Run more gently. Avoid that jarring feeling! Experiment with your running style; do anything that feels less like you’re slamming your feet down. We can definitely run more softly if we try to,35 most easily by shifting to a forefoot impact and basically running more like a tiptoeing cartoon thief; barefoot running or minimal shoes help with this, as they strongly discourage heel impact and so we shift our impact to the forefoot. But there are trade-offs! Forefoot impact undoubtedly shifts the burden between tissues, which might help solve patellofemoral pain while risking new injuries. More about this in the next section.

  Alternatively, another strategy for running softer is probably less prone to dicey trade-offs: slow down and take smaller steps! Basically just run less aggressively, period.

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Related Reading

Most of the knee pain information on PainScience.com is about patellofemoral syndrome and iliotibial band syndrome, the two most common runner’s knee conditions, typically causing pain on the front and side of the knee respectively (learn more about the difference). Many related articles:

Notes

1. Lieberman DE, Bramble DM. The evolution of marathon running: capabilities in humans. Sports Med. 2007;37(4-5):288–90. PubMed #17465590 ❐ “Human endurance running performance capabilities compare favourably with those of other mammals and probably emerged sometime around 2 million years ago in order to help meat-eating hominids compete with other carnivores.”
2. The original quote is from Benjamin Franklin: “The definition of insanity is doing the same thing over and over and expecting different results.”
3. NYTimes.com [Internet]. Kolata G. For Runners, Soft Surface Can Be Just as Hard on the Body; 2016 December 29 [cited 22 Nov 15]. “Exercise researchers say there are no rigorous gold-standard studies in which large numbers of people were assigned to run on soft or hard surfaces, then followed to compare injury rates. … It’s too hard to recruit large numbers of people willing to be randomly assigned to one surface or another for their runs.”
4. Ponzio DY, Syed UA, Purcell K, et al. Low Prevalence of Hip and Knee Arthritis in Active Marathon Runners. J Bone Joint Surg Am. 2018 Jan;100(2):131–137. PubMed #29342063 ❐

   In this survey of 675 marathoners, there was no link between current arthritis symptoms and their running history, and they had a lower rate of arthritis than the general population. That is, no matter how much they ran, they had the same low rate of arthritis: about 9%, compared to 18% in non-runners. Obviously this is nice news that challenges the assumption that relentless “pounding” on the road is hard on joints, but for better evidence based on longer-term data, see Lo.

5. Ferris DP, Liang K, Farley CT. Runners adjust leg stiffness for their first step on a new running surface. J Biomech. 1999 Aug;32(8):787–94. PubMed #10433420 ❐

   This simple experiment showed that runners adapt to changes in the hardness of the surface they are running on with amazing speed — just a single step — as measured in terms of maintaining the height of their centre of mass. Importantly, this nearly instantaneous adaptation only occurs with an expected change on familiar surfaces, but we are probably pretty quick with unexpected and unfamiliar surface changes as well.

6. We have a couple of main biological shock absorption tricks:

   • Muscle tuning is the dynamic dampening of impact vibrations with precisely timed muscle contractions — a very cool system (Boyer et al). And quite exotic (and likely not embraced by all experts).
   • Springing is the more obvious one: we adjust the springiness of our entire body by being bendier. Harder surface? More bending! Softer surface? Less bending! (Ferris et al) It’s obvious in an extreme example, like bouncing on a trampoline, where you can keep your knees straight; but jump down just one metre onto concrete, and you’ll have to bend your knees quite a lot. We do the same thing much more subtly when we walk and run.
7. van der Worp H, Vrielink JW, Bredeweg SW. Do runners who suffer injuries have higher vertical ground reaction forces than those who remain injury-free? A systematic review and meta-analysis. Br J Sports Med. 2016 Apr;50(8):450–7. PubMed #26729857 ❐
8. Altman AR, Davis IS. Prospective comparison of running injuries between shod and barefoot runners. Br J Sports Med. 2016 Apr;50(8):476–80. PubMed #26130697 ❐ For this test, 200 experienced runners were studied over the course of a year. The results are clear and unsurprising: there was no important difference in injury rates, just the types of injuries. Each was better in some ways, worse in others. Although the paper emphasizes “fewer overall injuries” for barefoot runners, injury rates are what matters — the number of injuries per 1,000 kilometres, say — and they were “not statistically different between groups due to significantly less mileage run in the barefoot group.”
9. Several papers by Clare Ardern et al. have shown that a positive view towards return to sport is important for a successful return (see Ardern 2013, Ardern 2014, Ardern 2015, Ardern 2015). Unnecessarily fearing the surface you run on is the opposite of a “positive view.”
10. Bodies have to work to minimize the effect of jarring steps on any one anatomical structure. As described above, we absorb shock mainly with two tricks: muscle tuning and springing. Every precisely timed vibration-dampening contraction takes energy and yanks on our anatomical rigging; every bit of extra springing takes joints a little further into flexion, with a little more muscle power to control the movement. We’re good at it … but it’s work.
11. Bohne M, Abendroth-Smith J. Effects of hiking downhill using trekking poles while carrying external loads. Med Sci Sports Exerc. 2007 Jan;39(1):177–183. PubMed #17218900 ❐ PainSci #56827 ❐

    For this study, fifteen experienced male hikers walked down a 36˚ test ramp 30 times with poles and 30 times without, and with three different loads: nothing, a light pack, and a heavy pack (30% of bodyweight). A force plate in the ramp measured the intensity of their foot impact, and they were videotaped to get measurements of their joint movement. Consistent with other cited research, the use of poles resulted in significantly reduced forces, movement, and power around the knees and ankles. Interestingly, it didn’t matter how heavy the pack was: “packs only resulted in a larger power generation at the hip.”

12. Humans have a couple main biological shock absorption tricks: one is to dampen vibrations with precisely timed muscles contractions (which is very cool, see Boyer 2004), and the other is to bend like a complex spring (Ferris 1997). The springing is really obvious in an extreme example, like bouncing on a trampoline, where you can keep your knees straight; but jump down just one metre onto concrete, and you’ll have to bend your knees quite a lot. We do the same thing much more subtly when we walk and run. We’re amazing at making much finer, faster adjustments to surface rigidity when running (see Ferris 1999).

13. Even though Altman et al showed that injury rates were the same in barefoot runners, there’s an incredibly important caveat: the barefoot runners they tested put in just 24km/week, while runners in shoes ran 41km/week! Injury rates invariably go up with training volume. So what would the injury rate have been for the barefoot runners if they had almost doubled their distance to match the shod runners? Probably higher! As Alex Hutchinson put it for Runner’s World, “The only way the comparison has any relevance is if they’re arguing that barefoot running reduces injuries by preventing you from running as much as you’d like.”

    It’s all still debatable, but in my opinion I think both common sense and some evidence now suggest that pounding the pavement without padding is almost certainly more injurious — which suggests that pounding pavement is probably more stressful than pounding trail.

14. van der Worp H, Vrielink JW, Bredeweg SW. Do runners who suffer injuries have higher vertical ground reaction forces than those who remain injury-free? A systematic review and meta-analysis. Br J Sports Med. 2016 Apr;50(8):450–7. PubMed #26729857 ❐
15. Phan X, Grisbrook TL, Wernli K, et al. Running quietly reduces ground reaction force and vertical loading rate and alters foot strike technique. J Sports Sci. 2016 Sep:1–7. PubMed #27594087 ❐

    This was a study of the relationship between the loudness of foot strikes in running and several technical measures of forces on the lower limb. Twenty-six runners were tested when instructed to run quietly versus normally. Most runners (77%) switched to a forefoot running style. The surprise finding is that natural variation in footstrike volume has no direct relationship with smaller, slower impact forces when running normally. In other words, there are some quiet runners with a surprisingly jarring gait, and some loud runners who aren’t pounding nearly as hard as you’d think. Odd.

    Not so surprisingly, actually trying to run quietly does soften footstrike.

    This science brought to you by the Department of Well Okay Then Thanks I Guess?

16. Which is, by the way, a nice demonstration of an interesting training principle: it’s easier to modify technique by focussing on an external or abstract goal, rather than the biomechanics of the technique itself. In this case, the abstract goal of being quiet or “sneaky” evokes forefoot running almost like magic, without having to devote the slightest attention to the specifics of how to run more quietly.
17. van der Worp 2016, op. cit. “The loading rate was higher in studies that included patients with a history of stress fractures and patients with all injury types, both compared with controls. Only studies that included patients with a history of symptoms at the time of kinetic data collection showed higher loading rates overall in cases than in controls.”
18. Davis IS, Bowser BJ, Mullineaux DR. Greater vertical impact loading in female runners with medically diagnosed injuries: a prospective investigation. Br J Sports Med. 2016 Jul;50(14):887–92. PubMed #26644428 ❐
19. Zadpoor AA, Nikooyan AA. The relationship between lower-extremity stress fractures and the ground reaction force: a systematic review. Clin Biomech (Bristol, Avon). 2011 Jan;26(1):23–8. PubMed #20846765 ❐

    This study of studies tries to determine 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). They 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 it’s not how hard you hit the ground, but how fast you hit it. However, the science was murky on something important: the correlation identified is statistically “significant,” but the size of the correlation is not impressive. 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.

20. Milgrom C, Burr DB, Finestone AS, Voloshin A. Understanding the etiology of the posteromedial tibial stress fracture. Bone. 2015 Sep;78:11–4. PubMed #25933941 ❐
21. The bone resisting bending rather than resisting longitudinal compression. Sheer strain could explain the oblique stress fractures more often seen in young adults.
22. Kluitenberg B, van Middelkoop M, Smits DW, et al. The NLstart2run study: Incidence and risk factors of running-related injuries in novice runners. Scand J Med Sci Sports. 2015 Oct;25(5):e515–23. PubMed #25438823 ❐
23. Tessutti V, Ribeiro AP, Trombini-Souza F, Sacco IC. Attenuation of foot pressure during running on four different surfaces: asphalt, concrete, rubber, and natural grass. J Sports Sci. 2012;30(14):1545–50. PubMed #22897427 ❐ A study of the relationship between “in-shoe pressures” and asphalt, concrete, and natural grass in 47 recreational runners. Each of them ran 40 metres at about 12kph with Pedar X insoles, which measure pressures on the bottom of the foot. Running on asphalt and concrete produced the same pressures, but pressures on were about 9–16% less. Note that measuring forces only in the foot can only tell us so much.
24. Fu W, Fang Y, Liu DM, et al. Surface effects on in-shoe plantar pressure and tibial impact during running. Journal of Sport and Health Science. 2015 Dec;4(4):384–390. PainSci #53552 ❐ This paper with surprising results is unusually well-written, with a good introduction reviewing the subject background. They measured two key impact variables in 13 male recreational runners (all heel-strikers) at 12 km/h velocity on concrete, synthetic track, natural grass, a normal treadmill, and a treadmill equipped with a cushioning. Plantar pressures were measured with an in-shoe pressure system, and tibial shock (peak positive acceleration) was measured with an accelerometer at the top of the shin. Almost no differences were observed in these forces on any of the surfaces!
25. Belavý DL, Quittner MJ, Ridgers N, et al. Running exercise strengthens the intervertebral disc. Scientific Reports. 2017 Apr;7:45975. PubMed #28422125 ❐ PainSci #53606 ❐
26. But you’ll also hear it from countless physical therapists these days, so let’s run with it for the sake of this point. For a full discussion about this, see Does Hip Strengthening Work for IT Band Syndrome?.
27. Lenhart R, Thelen D, Heiderscheit B. Hip muscle loads during running at various step rates. J Orthop Sports Phys Ther. 2014 Oct;44(10):766–74, A1–4. PubMed #25156044 ❐ PainSci #53657 ❐ Using computer modelling of their own design, the authors claim to have produced evidence of “substantially” more powerful gluteus medius and minimus contractions than any other hip muscle: “The sum of peak forces from the gluteus medius and minimus, 2 primary hip abductors, was 3.5 times that of the gluteus maximus, a primary hip extensor.”
28. For more detail, see another article on PainScience.com, Eccentric Contraction: A weird bit of muscle physiology.
29. Franklyn-Miller A, Roberts A, Hulse D, Foster J. Biomechanical overload syndrome: defining a new diagnosis. Br J Sports Med. 2014 Mar;48(6):415–6. PubMed #22983122 ❐ PainSci #53656 ❐
30. Werner RA, Gell N, Hartigan A, Wiggerman N, Keyserling WM. Risk factors for plantar fasciitis among assembly plant workers. PM R. 2010 Feb;2(2):110–6; quiz 1 p following 167. PubMed #20193937 ❐
31. Roger Davies was quoted in a Canadian Broadcasting Corporation article published Mar 3, 06.
32. The rationale for this product is discussed thoroughly in my orthotics article, but basically the idea is that shoes of this type “reduce lower limb muscle forces,” (Wunsch et al) because the surface is giving you some energy back.
33. Verdejo R, Mills NJ. Heel-shoe interactions and the durability of EVA foam running-shoe midsoles. J Biomech. 2004 Sep;37(9):1379–86. PubMed #15275845 ❐

    Science news flash! Shoes wear out: “Scanning electron microscopy shows that structural damage (wrinkling of faces and some holes) occurred in the foam after 750 km run. Fatigue of the foam reduces heelstrike cushioning, and is a possible cause of running injuries.”

34. Kong PW, Candelaria NG, Smith DR. Running in new and worn shoes: a comparison of three types of cushioning footwear. Br J Sports Med. 2009 Oct;43(10):745–9. PubMed #18801775 ❐

    When shoes wear out, the biomechanics of running do change. Kong et al tested 24 runners before and after 200 miles of road-running in the same pair of shoes. There were a few minor changes: longer stance phase, less forward leaning, and less ankle flexion. Hip and knee angles were unchanged. (Also, 200 miles is not much — a strangely low number for this study, actually — and the impact on biomechances may only just be getting started by then.)

    I do recommend replacing your shoes when they begin to show obvious signs of wear. The risk of running in decrepit shoes may be small, but there’s not much reason to take that risk — just the modest cost of buying shoes somewhat more often. It’s not like you weren’t going to buy new shoes eventually! On the other hand, this data makes it pretty clear that replacing shoes while they still look fine isn’t really going to make much of a difference.

    Does running on concrete mess up your knees?

    Cons: Concrete is the least forgiving of running surfaces, according to Timothy Noakes, author of “Lore of Running.” When running on concrete, the ground doesn't absorb any of the shock that travels through a runner's feet, knees, hips and lower back. This can lead to an increased injury risk.

    What is the best surface to run on for your knees?

    Flat grass is the best surface to run on because it has the least impact on your bones and joints, experts say. Its softness also causes your muscles to work harder, burning more calories and building more strength. Dirt, gravel and woodland trails are also good choices.

    How can I run without damaging my knees?

    Tips for protecting your knees when you run.

    Start slowly and conservatively. Avoid going too hard, too fast. ... .

    Stretch before and after you run. If your muscles are tight, you're more likely to run with bad form and injure yourself. ... .

    Consider compression sportswear..

    Why do my legs hurt after running on concrete?

    Shin splints, medically known as medial tibial stress syndrome, is pain on the anterior or medial areas of the shin bone. It typically happens when runners increase their distance too fast and run on hard surfaces like concrete. The symptoms are shin pain, swelling, and tenderness.