Sunday, October 21, 2012

Injury Series: Medial tibial stress syndrome ("shin splints") as a bone injury to the tibia

Medial tibial stress syndrome is related to tibial stress reactions and stress fractures, which you can read about here
For an in-depth discussion of returning to running following a bone stress injury like medial tibial stress syndrome, see this article

Medial tibial stress syndrome (MTSS), or shin splints, is perhaps the best-known running injury to the average citizen.  Aching or throbbing shins is an ailment that many new runners and many athletes in all sorts of impact-related sports, like volleyball, basketball, and sprinting, deal with on a regular basis.  Unlike some running injuries, which appear to be non-discriminatory—both Joe Jogger and Ryan Hall suffer from plantar fasciitis, for example—medial tibial stress syndrome seems to be an issue encountered more often by new or seasonal athletes (though not exclusively).  The reasons for this tie in closely with its root causes, which we’ll get to in a moment.  Shin splints also have a complicated and fascinating relationship with tibial stress fractures, which we will also get to later on in the article.  If you’ve read my Injury Series post on tibial stress fractures, you might see some familiar material.  But first, as usual, we need a bit of anatomy.

Anatomy and terminology

The tibia is your “shinbone,” the long, straight bone that forms the front of your leg.  The tibia carries a significant portion of the impact that goes up your leg when you hit the ground, and it also serves as an attachment point for the muscles that control your foot and ankle, all the way from the relatively small ones like the flexor digitorum longus muscle, which flexes your little toes, to the calf muscles, which are the engine below the knee for forward movement.  The medial edge of the tibia runs up the inside of your leg and borders your calf muscles.  The “stress” part of medial tibial stress syndrome just means that the condition is demonstrably associated with weight-bearing stress from exercise.  Other more exotic names for medial tibial stress syndrome have cropped up, like “exercise-related lower leg pain,” but at this point, medial tibial stress syndrome or MTSS seems to be the predominant and most useful term.  In this article, I’ll use these terms interchangeably with “shin splints,” the less-descriptive and colloquial term for this injury, but keep in mind that the medically-correct term is medial tibial stress syndrome.   


The most obvious symptom of MTSS is, of course, shin pain.  The pain usually presents as an aching, burning, or throbbing feeling along the inside edge of the shinbone, usually dispersed over several inches along the shin.  The shin (or often, both shins) gets progressively more painful throughout the duration of a run or workout.  Early cases of shin splints might be nothing more than a bothersome ache near the end of a long run, but can progress to the point where even short jogs cause pain.  There may also be some tenderness along the medial edge of the tibia.  One review study recommends that medial tibial stress syndrome be defined as pain which extends for at least 2 inches along the middle to bottom-third of the shin, which is aggravated by weight-bearing and subsides with rest.1  Cases of shin pain which is localized to a very small area should be examined by a doctor to rule out a stress fracture.  X-rays are insufficiently accurate to rule out a tibial stress fracture, so your doctor should use a bone scan or, preferably, an MRI, to diagnose your injury. 

Mechanism of injury

Usually, this is where I’d jump into the nitty-gritty details about diagnosing MTSS and the risk factors for it, but it’s at precisely this point where the story begins to get interesting.  Say an orthopedist sees two runners with shin pain.  Both get a sharp pain in the medial tibia about a third of the way up, but the first patient has very localized pain over an area half an inch long that’s tender to the touch, while the second has much more diffuse pain that’s spread out over several inches.  Most orthopedists would suspect that patient #1 has a stress fracture and would order an MRI or bone scan to confirm, while patient #2 would likely be diagnosed with MTSS and referred for physical therapy.  But what’s the relationship between these injuries? Do they have different root causes? If patient #2 continues to train, could he or she develop a stress fracture? And are the causal factors the same?
The layers of tissue in the tibia, with periosteum highlighted in the lower left

Historically, medial tibial stress syndrome and tibial stress fractures were considered distinctly separate injuries.  Stress fractures were suspected to be the result of impact forces traveling up the leg, while MTSS was blamed on tensile forces from the muscles of the lower leg “pulling” on their origin points along the tibia. The shin pain from shin splints was assumed to be due to inflammation or irritation of tissue surrounding the bone.  Several authors conducted anatomic studies on cadavers and pointed to the flexor digitorum longus, soleus, or tibialis posterior muscles as the source of traction on the tibia.  They all proposed that the tugging of the muscles at their origin points caused inflammation of the periosteum, a “skin” of tissue that surrounds the tibia.2, 3, 4 

 However, these studies could not agree on which muscles were responsible for the traction and subsequent periostitis (inflammation of the periosteum).  Later anatomical studies and reviews concluded that the most frequent sites of pain from shin splints are too far down the leg to be a result of traction from any of the muscles that control the foot.4, 1  

The muscles of the lower leg do attach to the tibia (orange shaded areas), but are too far up the tibia to be the primary cause of medial tibial stress syndrome: pain most commonly occurs around 1/3 of the way up the tibia (red speckled shaded areas), where there are few or no muscle fibers to tug on the bone.
  Additionally, studies which actually examined samples of the periosteum in athletes with shin splints did not find strong evidence for the traction/periostitis paradigm.  In one study published in1982 by Johnell et al., researchers took samples of the tibia and periosteum from 20 athletes with shin splints, several with pain in both legs.5  Out of the 33 samples acquired of the periosteum, 13 showed inflammatory changes, but of the 35 bone samples, 22 showed some signs of increased metabolic activity.  A similar study, published in 2000 by Bhatt et al., took 32 tissue samples of the tibia and periosteum from 20 athletes.6  Of these, 21 samples of the periosteum showed abnormal changes, but only a handful exhibited signs of inflammation.  On the other hand, 16 of the 26 samples of tibial bone showed abnormal changes.

While sometimes helpful, studies which involve taking tissue samples have several problems associated with them.  First, the tissue acquired is usually from athletes with very severe and long-lasting shin pain.  Additionally, acquiring an adequate control group is quite difficult, since few healthy runners are keen on letting a group of doctors take a 3mm drill to their shinbone.  Finally, because of the nature of tissue samples, they can easily miss what you might call a “heterogeneous” injury: one which isn’t evenly distributed across the injured area.  As we’ll soon see, medial tibial stress syndrome is characterized by pockets of localized bone loss, which could have been easily missed by the drill bit.  This might explain why a lot of the tissue samples in Bhatt et al. and Johnell et al. appeared completely normal, even in seriously injured athletes.

Worsening of MTSS in a volleyball player
Fortunately, advances in medical imaging have allowed researchers to circumvent many of these limitations with high-resolution CT scans and MRIs.  Scans of athletes with MTSS have revealed that the bone of the tibia is definitely involved in the injury process.  In a landmark 1995 study, Fredericson et al. developed a grading system for MRI and bone scan results to categorize tibial stress injuries into medial tibial stress syndrome, tibial stress reactions, and tibial stress fractures.7  Mild forms of tibial stress injury are characterized by an abnormal signal for the periosteum, as well as a diffuse increase in bone synthesis in the tibia itself as seen on a bone scan.  As the injury progresses, the bone marrow becomes involved and signals from the bone scan become more intense, and finally, in true stress fractures, a fracture line can be seen on the MRI.  This is beautifully illustrated in the MR images to the left, taken in a 19-year-old female volleyball player who continued to train with shin splints.  The MRI clearly reveals the worsening of her condition after a week.  Fortunately, the authors report that this subject recovered with rest in under a month.  Additionally, the grading system of Fredericson et al. allows an estimate of how long it will take for the athlete to return to running.

Further work with CT scans has confirmed a definite role of bone injury in shin splints.  Michele Gaeta and colleagues at the University of Messina in Italy have published two fantastic studies on using MRI and CT scans to image the bone resorption process in both healthy training and medial tibial stress syndrome.8, 9  The series of cross-sectional CT scans of tibias below clearly demonstrates that the tibial cortex, the hard shell of the bone that gives it its strength, display abnormalities in athletes with shin splints. 

CT tibial cross sections of A) a healthy runner B) a healthy runner showing normal signs of bone resorption/growth (dots) C) a runner with medial tibial stress syndrome and marked areas of low bone density and resorption (arrows) D) a runner with MTSS and a larger area of osteopenia/low bone density and bone resorption associated with overloading of the tibia (arrows and arrowheads).  Adapted from Gaeta et al. and Gaeta et al.
However, the work of Fredericson et al. and Gaeta et al. have also highlighted an important fact that’s key to understanding the mechanism of injury in shin splints: many healthy athletes display mild abnormalities of the periosteum and the tibial cortex in MRI and CT scans! Herein lies the key to understanding the link between medial tibial stress syndrome, stress reactions, and true stress fractures.  All three are a result of excessive loading on the tibia.  This finding is bolstered by bone density studies which have shown that athletes with medial tibial stress syndrome have lower bone density in the tibia10 which seems to increase once they have recovered.11  Moen et al. succinctly summarize the findings as follows:1

There are four important findings that support the theory that bony overload forms the primary pathophysiological basis for MTSS: (i) on triple-phase bone scans the last phase is abnormal, showing that the bone and periosteum are involved (ii) on high-resolution CT scan the tibial cortex is found to be osteopenic, as can be seen in patients as well as in asymptomatic athletes as a sign of bone remodelling (iii) on MRI images, bone marrow oedema as well as a signal along the periosteum can be seen (iv) in patients with MTSS,  bone mineral density is reduced compared with controls, and when symptoms improve, the bone density returns to normal values.

 Bone loading and remodeling

One fundamental property of biological tissues in the human body is that they respond to stress; bone is no different.  When it’s subjected to stress, from running, jumping, or any other weight bearing activity, your tibia initiates a remodeling process through which it becomes stronger.  This is why impact activities promote a high bone density, and are encouraged as a method of preventing osteoporosis.  However, remodeling a bone is a rather lengthy process—it can take a month or two for your bone to adapt to a new stress, and during that window of time, your tibia can actually be weaker because of the way remodeling occurs.12  Just like remodeling your kitchen might entail tearing out some walls before you can put in new construction, your body has to resorb areas of bone tissue in the tibia before it can strengthen it.  This explains why bone resportion cavities are seen in healthy runners, as their body is adapting to the stress of training as it should.

But what causes the progressive weakening of bone in MTSS? The most likely explanation is that the stresses of training outpace the body’s ability to remodel the bone, so the problem becomes a compounding one: additional stress induces bone resorption in the tibia, which leaves the bone more vulnerable to additional stress.  Research to date indicates that tibial stress is not so much from compressive forces going straight down the tibia but from bending forces that cause small deflections in the bone.13, 14  However, a number of factors have been associated with medial tibial stress syndrome; first, we’ll review them, then we will examine how they might contribute to excessive tibial loading and what can be done about it.

According to Popp et al. and Bennell et al., damage to the tibia occurs due to bending in the sagittal plane.
Epidemiology—who gets it and why

Shin splints are a fairly common running injury. They account for 4-5% of all running injuries,15, 16 and 12-15% of high school cross country runners will suffer from MTSS at some point during a season.17, 18  Women are roughly twice as likely to get it as men.  As you might expect, many of the causal factors are related to underlying bone structure.

One exceptionally thorough 2008 study out of Monash University in Australia demonstrated that tibial geometry in both men and women are strongly linked to the development of both tibial stress fractures and medial tibial stress syndrome.19  Franklyn et al. used high-resolution CT scans to analyze the cross-sectional geometry of four groups of people: athletes with tibial stress fractures, athletes with medial tibial stress syndrome, healthy athletes, and healthy sedentary people.  Men and women were split into subgroups within each category.  Using a mechanical engineering approach, Franklyn et al. used computational analysis to calculate a variety of mechanical properties of the tibias of the various subjects, many of them related to how well the tibia resists bending forces.  Their findings were quite impressive:

  • In men with tibial stress fractures or MTSS, the tibia was ill-equipped to resist bending forces as a result of a smaller cross-sectional area compared to the healthy athletes
  • In women with tibial stress fractures or MTSS, the tibia was also less resistant to bending, but because of the way in which the bone was distributed about the central axis of the tibia.  The leading edge of the tibia was further away from the center of the bone, which would lead to increased strain during backwards bending.
  • In all groups, the bone geometry of the injured athletes and the sedentary controls was similar, but significant differences existed when comparing these groups to the healthy athletes.
  • Bone geometry differences that predicted stress fractures also predicted medial tibial stress syndrome
This last point in particular adds further evidence, in my opinion, to the idea that medial tibial stress syndrome and tibial stress fractures exist on a continuum of tibial bone injuries.  I should note, however, that Franklyn believes that they are related but different injuries.20 Her reasoning is that not all cases of MTSS lead to stress fractures, and that MTSS is a diffuse injury, while stress fractures are localized.  I believe that both of these can be explained by variations in bone remodeling rates. 

Franklyn et al. also acknowledged that it’s likely that bone density plays a role in the development of tibial stress injuries in women, though they did not measure it in their study.  Indeed, we know from other studies that bone density is related to stress fractures in women, but not men.  The menstrual cycle plays a key role here, as disturbances in menstruation brought about by inadequate nutrient intake and disordered eating lead to hormonal imbalances and a reduction in bone density, a condition known as the female athlete triad.  Studies on stress fractures in women have found that missing more than one or two menstrual cycles a year leads to a substantial increase in stress fractures and a drop in bone density.21  Differences in bone density may explain why women suffer disproportionately from shin splints.

Some studies (but not all)22 have also connected calf size and strength with medial tibial stress syndrome.23  In theory, larger and stronger calf muscles encourage the tibia to become stronger and thicker, a phenomenon observed in some studies of women at risk for tibial stress fractures.13  In addition to promoting stronger bones, the calf muscles also absorb impact forces directly.24  A weakened calf musculature would require the tibia to take more of the pounding during impact.  Indeed, a 2007 study found that athletes of both genders who have medial tibial stress syndrome have demonstrably weaker calf muscles, as measured by a single-leg calf raise test.25 
Biomechanical factors

While early work linked foot pronation with MTSS, especially in recreational sports participants and military recruits, more modern studies in runners have been less clear.  Two very similar prospective studies on large groups of high school cross country runners found conflicting results: Bennett et al. found that navicular drop, a proxy measurement for foot pronation, was a strong predictor of shin splints among high school runners,17 but a later study by Plisky et al. found no relationship between the two, and cited three other large studies on runners which also found no relation between pronation and MTSS.18  Bennett et al. fired back again in July of this year with a larger prospective study of collegiate cross country runners which found that runners who pronate while standing are more likely to get MTSS; additionally, they found no link between calf endurance and the propensity to develop shin pain.22  Interestingly, Bennett et al. propose that the link between calf endurance and shin splints found in some studies may simply be a proxy for overall fitness: presumably, a fitter athlete would have strong calves, and also be less prone to MTSS, though perhaps not entirely because of his or her calf strength.  It’s well established that poor physical fitness is a predisposing factor to MTSS in military recruits, and I suspect the same relationship would hold for runners—less-fit runners would presumably have been training less or not at all, and hence would not have the tibial bone strength of a runner training full-time. 

If pronation is a factor, it’s likely because pronation of the foot shifts the ground reaction force toward the inside of the leg, putting additional pressure on the medial edge of the tibia.  While the prevailing opinion among biomechanics researchers appears to be that the main cause of tibial stress is bending in the sagittal plane (a “backwards” bending of the tibia), prominent podiatrist Kevin Kirby argues that increased pronation leads to bending in the frontal plane (a “sideways” bending of the tibia), which he believes can be treated with custom foot orthotics.26  His logic is that a medial wedge, an outward slant in an orthotic underneath the inside of the foot, will shift forces laterally, taking strain off the medial tibia.  While it’s an interesting proposition, and explains why some runners find relief from MTSS in custom orthotics much better than the old “pronation control” paradigm, any experimental evidence for this idea is still lacking.    

Finally, given the strong link we’ve established between shin splints and more serious tibial injuries (stress reactions and fractures), it is reasonable to suspect that a high impact loading rate is connected with MTSS, since it’s been implicated in tibial stress fractures.27  Franklyn et al. argue that tibial bending is not caused by the impact forces, but the active forces which follow, during the “push off” phase of gait.20  Both opinions may well be right: let’s not forget that impact forces and active forces are intimately related when we consider stride frequency.  Taking an extreme case, bounding for distance is a “running gait” with a very low cadence, very high impact forces, and very high active forces.  At the other end of the spectrum, running at a slow speed with a high cadence is a gait with low impact forces and low active forces as well. 

It's uncertain whether the impact peak (left) or the active peak (right) of the overall ground reaction force is to blame for medial tibial stress syndrome.  Both may be involved.  Fortunately, strategies to reduce one tend to reduce the other.
Franklyn also describes a highly detailed computer model that demonstrated that overloading on the tibia appears to be the result of high tensile stress (due to bending forces) on the external surface of the medial side of the tibia, and additionally, that this stress peaks during the active part of the gait cycle.  When looking to prevent or treat MTSS, we’ll have to look for strategies which can decrease the bending from the active force peak (and/or the impact peak), or at least strengthen the bone’s resistance to it. 

Computer model which predicts that the maximum stress on the tibia is a result of bending forces encountered during the "push off" phase of gait.  From Franklyn and Oakes.20
Prevention and treatment

Happily, most cases of medial tibial stress syndrome are mild and resolve quickly.  In the Plinsky study on high school cross country runners, the majority of cases resolved with only 1-4 days of missed training.  It’s reasonable to suspect that the root cause of MTSS in most cases is simple overloading of the tibial bone.  Jumping from a relatively sedentary lifestyle into a high volume of running (or any other impact activity for that matter) can load the tibia with more force than it can handle.  The tibia will eventually adapt to the new load, but bone remodeling appears to be a fairly slow process.  And, problematically, there is a window of time during the remodeling process where the tibia is actually more vulnerable to stress. 

Despite its prevalence in athletes and military recruits, there have been very few studies of treatments for MTSS, especially in runners.  No solid treatment or prevention protocol has been identified, so as with tibial stress fractures, we will have to do some deductive reasoning using what we know about the causal factors to predict what might prevent or treat shin splints.  To this end, treatment and prevention protocols should be oriented on reducing the stress on the shin and improving the strength of the tibia.

Reducing tibial stress

Decreasing the shock that goes up the shin should reduce symptoms and give the body a better shot at strengthening the tibia even as training continues.  From a biomechanical perspective, two surefire ways to reduce tibial stress from impact and from active force peaks are by increasing your stride frequency by 10% or so and by slowing down the pace on your runs.  Many runners have a tendency to drop their stride frequency when they slow down, so you’ll have to check your cadence regularly to make sure you’re not getting lazy with your running form.  While there’s nothing magical about a stride frequency of 180 steps per minute, most elite runners (and, in my observation, most injury-resistant runners) have a cadence of at least 180, even at slow paces, and it’s very difficult to overstride at stride frequencies of 180 or above.  The best way to check your stride frequency is to count the number of times your right leg hits the ground while running for 30 seconds, then multiply by four.  Ideally, you’d count 45 or more right-foot strikes in 30sec.  If your cadence is lower than this, moving right up to 45 will feel unnatural, so you’ll have to spend some time to work your way up.  Check often, and if you can, try running behind a friend who has a stride frequency of 44-45 and matching his or her cadence.  Slowing down the pace on your runs is just a matter of self-control.  It seems like this is a problem for young, highly talented runners, since they can maintain a very fast training pace on account of their raw fitness but have not yet allowed their bones to adapt to the stresses of training.  If this sounds like you, try backing off your training pace by 30 or even 60 seconds per mile.  Remember that there’s good evidence that the harder you push off from the ground, the higher the stress on your tibia.  Plenty of extremely fit runners trot along at 7 or 8-minute miles in training!

Decreasing your training volume or intensity is another obvious way to reduce stress on your tibia, but is probably the least palatable treatment to the serious runner.  While you’re virtually certain to recover with a few weeks’ rest, this is a non-starter for any in-season athlete.  A better approach might be to cut out any unnecessary mileage: shorten warm-ups and cool-downs, lower the distance of your easy days, and don’t push too hard when working out.  Figuring out how to calm down MTSS while still continuing to train and race is a difficult and highly individual challenge, so I can’t offer any more broad advice on that front.  Do keep in mind that MTSS and tibial stress fractures likely exist on a spectrum of tibial stress injuries, so foolishly pressing ahead with shin pain could land you in a boot for a month or more.

Many runners and coaches think that running on a softer surface like dirt or grass will reduce tibial loading vs. running on concrete or pavement, but that isn’t borne out by the research.  In fact, some theoretical work suggests that tibial shock might be higher on softer surfaces.  This is because of the way your body adapts to running on surfaces of varying stiffnesses.28  In order to maintain a consistent path for your center of gravity, your body adjusts the stiffness of your legs based on the surface you’re running on.  So, when you run on a hard surface in thin shoes, your legs become more compliant, and in contrast, in thick shoes on a soft surface, your legs become stiffer.  Having high leg stiffness is one factor that’s been connected with tibial stress fractures29—a few researchers hypothesize that running with a high leg stiffness stresses the “firm” tissues of the leg (the bones and the joints), while a low leg stiffness stresses the soft tissues (the muscles and tendons).  This leg stiffness approach may explain why some runners have found that barefoot running or minimalist shoes have allowed them to overcome MTSS when custom orthotics, pronation control shoes, and icing failed: the high stiffness of the ground and shoe (if any) forced their legs to become much more compliant, transferring stress from the tibia to the calf and shin muscles.  If you are feeling particularly adventurous and want to try out an untested treatment protocol, or if you are at your wit’s end after having been failed by other more cautious treatment methods, you might consider switching to running in thinner, firmer shoes on a harder surface.  Needless to say, this is a rather drastic step, so this really ought to be a last resort.  Additionally, I recommend avoiding wearing extremely thin shoes like the Vibram FiveFingers on very hard surfaces like asphalt and concrete, as some worrisome reports suggest this might increase your risk of metatarsal stress injuries.30

However, this entire paradigm rests on the central nervous system working properly in injured runners.  As pointed out by podiatrist Ian Griffiths on Podiatry Arena, it’s possible that injured runners might have a leg stiffness that’s “stuck” at a high level.  In this case, running on hard surfaces would be more injurious, as it would lead to a mismatch between the surface and the leg stiffness.  If this were the case, runners with shin splints should stick to softer surfaces until their central nervous system “resets.”  My intuition tells me that the CNS still works properly in injured runners, but things are often not as they seem in this sport! Check out this post for some more thoughts on this concept.

Despite all of this blustering about theory, many runners still find that soft surfaces are kinder to their shins.  Why is this? It could be just a perception bias, but I suspect that surface irregularity plays a role too.  Soft, natural surfaces, like gravel roads, dirt trails, and grassy fields, tend to be much more irregular than a concrete sidewalk or asphalt road.  This might mean that each step stresses your foot and leg slightly differently, distributing stress across more areas of tissue and perhaps sparing your shins.

Another reason why runners sometimes find their shin issues resolving when they begin to run in minimal or no shoes is the resultant change in running form.  It’s well-documented that running barefoot results in a flatter foot placement, and forefoot or midfoot striking is much more prevalent in habitual barefoot runners than in the athletic population at large.31  While a forefoot or midfoot strike (or even a flatter heelstrike) has not been proven to be any “better” than normal heelstriking, theory does indicate that these footstrike styles do transfer loads from the shin and knee to the foot, ankle, and calf muscles.  In the case of medial tibial stress syndrome, this could also result in lower impact loads on the tibia.  However, you’re introducing new stresses on the metatarsals, Achilles tendon, and calf muscles, and a drastic alteration in running form is a very high-risk endeavor for anyone but a complete novice.  

On the other hand, some runners have also found that custom orthotics allow them to overcome MTSS.  Two studies of military recruits did find that custom orthotics can prevent shin splints,1 but to date no studies have investigated the benefits of orthotics in a non-military setting.  If custom orthotics do have any benefit in preventing or treating MTSS in runners, the mechanism is likely best explained (for now) by either Kevin Kirby’s hypothesis that supporting the medial side of the foot brings the ground reaction force more in line with the tibia, reducing bending in the frontal plane26 or by Benno Nigg's hypothesis, that insoles which encourage your body's "preferred path of motion" reduce tissue stress.  While Kirby's theory has no experimental backing and Nigg's only has a few experimental studies to its name, it may be worth trying a pair of PowerStep or SuperFeet insoles in your shoes, as this will only cost you about $40.  Custom orthotics are significantly more expensive, but may be worth trying if you are having long-standing shin pain.

A less risky option to unload the tibia is to strengthen the calf muscles.  As proposed by Madeley et al.,25 runners with MTSS may have poor calf endurance compared with healthy controls, and in women, smaller calf muscles have been linked with a smaller and weaker tibia.13  Unfortunately, there’s no agreement yet on what constitutes a “good” calf strengthening regimen.  Single-leg calf raises are a good place to start.  Looking back at successful strength exercise routines for other injuries, it’s likely that a successful program would involve multiple sets of single-leg calf raises, perhaps several times a day.  A hypothetical program might start with 3x15 single leg calf raises (on both sides) twice a day, progressing towards 3x30. 

Some coaches and athletic trainers have also found success in strengthening the other muscles of the lower leg that control the foot and ankle.  While the calf muscles absorb the bulk of the impact traveling up the leg, it’s probable that the smaller muscles play a role too.  Russ Ebbets, a chiropractor and lecturer on track and field, developed a six-part “foot drill” routine that’s been used by various sports programs with the goal of reducing foot and lower leg injury.  While there’s no scientific evidence for its efficacy, I’d be remiss to leave this routine out.  Franklyn et al. also mention that some studies have connected weak foot inverter muscles with MTSS, and that perhaps some of the excessive pronation in runners with MTSS is due to “dynamic” pronation (because of weak foot inverter muscles), giving credence to the “inside up” exercise in Ebbets’ foot drill routine.20  The foot drill routine, presented below, should be done every day for about 10-20m for each drill.  Ideally, the drills are all done barefoot on a soft surface. 

Russ Ebbet's six foot drills.  They should be done for 10-20m each, without shoes on a soft surface if possible.
Improving tibial strength

Despite all of the above treatments, to fully recover, you need to allow your tibia to become stronger.  By far the most important factor in doing so is TIME—current literature indicates that the bone remodeling process takes several months to fully complete.  The window in which bone resportion makes the tibia more vulnerable to stress is around 30-45 days after the initial increase in stress, at least according to a paper by Belinda Beck at Stanford University.12  This corresponds well to studies of military recruits, which find that incidence of stress fractures peak within the first month of basic training.  I cannot stress enough that an intelligent, gradual training program is the best way to increase tibial bone strength.  Runners, when healthy, have significantly higher bone density than sedentary people, and the benefits of this extend well beyond resistance to stress fractures.  The considerations below are important, especially for runners with chronic cases of MTSS, but for most runners, gradual progression of training is the ideal way to build up bone strength.  Interestingly, the kinetics of bone remodeling suggest that perhaps the best way to progress with your mileage if you are prone to shin splints is not a simple 10%-every-week model. 

Taking periodic “down weeks” every three or four weeks will give your shins a break from the continual strain of training.  So, your mileage progression might look like this:


Another option is what you might call an “equilibrium” approach, as advocated by Jack Daniels.  In this method, you increase your mileage by a larger amount but take several weeks to adapt to the new volume.  In this case, your mileage progression might look like this:


Sometimes, despite following an intelligent training progression, runners still find themselves beset by shin problems.  In this case, it’s time to think about what else could be affecting the strength of your tibia.

For women, these concerns revolve mostly around nutritional and hormonal well-being.  Too many female runners miss their menstrual period (amenorrhea) due to inadequate caloric intake and disordered eating, a condition known as the female athlete triad.  While the details of this are complicated, the end result is undesirable changes in hormone levels, which ultimately lead to a loss of bone density and an increased risk of tibial stress injury.21  It’s worth repeating that female athletes missing their period on a regular basis is a very serious issue whose consequences are far greater than simply being at an increased risk for shin splints.  If you exhibit signs of disordered eating, including fatigue, weight loss/a low BMI, a preoccupation with food/weight, and amenorrhea, seek help from your coach and family doctor. 

On the preventative front, one study of female navy recruits also found that taking a calcium and vitamin D supplement every day, totaling 200% of the RDV of both, decreased the risk of a stress fracture by 25%.32  Given the link between lowered local bone density and MTSS, it’s possible that such a regimen would also decrease the risk of medial tibial stress syndrome.  Men may also benefit from calcium/vitamin D supplementation, though this too is unproven. 

Finally, it’s worth rehashing that calf strength and size may be linked to tibial strength.  In one paper, Popp et al. link bone size with muscular cross-sectional area—that is, the smaller your calf muscles, the weaker your tibia.  This may be because the tibia responds to the maximum forces it encounters, and these occur not during impact, but during active force production (when you push off the ground).  If you have weak calf muscles, your tibia will not encounter a large stimulus to become stronger.  However, if the mechanism of injury is impact (not active forces), you have a recipe for trouble.  This theoretical link may not be accurate, but at the end of the day we still have solid experimental proof linking small calf muscles to slender tibias.  Additionally, even if calf strength per se is not linked to MTSS, doing lower leg strengthening exercises with weights is a great way to strengthen the tibia anyhow, as one 2009 study demonstrated that weight training increased tibial bending resistance in young women.36  Squats, lunges, and calf raises all strengthen the lower leg muscles, but perhaps more importantly, also progressively load the tibia, encouraging it to become thicker and stronger.  The specifics of an “ideal” weight program for runners are well beyond the scope of this article, and not really my area of expertise anyhow, so I’ll let you do the legwork on that.  Road to the Top by Joe Vigil and Better Training for Distance Runners by David Martin and Peter Coe both have chapters on weight and strength training. 

Directions for future research

When doing literature research for this article, I was surprised at the lack of scientific enthusiasm for studies on treating and preventing medial tibial stress syndrome.  With most other Injury Series articles, I was able to identify several studies of various treatment protocols, even though many of them were not effective.  In the case of MTSS, there are very few studies on treating and preventing it, and among those that do exist, almost all are on military recruits.  While military studies can be helpful, there are obvious differences between marching with a weighted pack for several miles a day on little sleep and the normal training of a recreational or competitive runner.  As we saw with foot pronation, some factors which are clearly linked to the development of shin splints in military populations are much more controversial in runners.

One interesting area of research is extracorporeal shockwave therapy or ESWT.  While ESWT has been pursued more vigorously as a possible treatment for connective tissue problems like plantar fasciitis, one study from July of this year found that it significantly improved recovery time from MTSS.33  While this study was reasonably large (42 athletes, all of which had been suffering from shin splints for at least three weeks), more research needs to be done on shockwave therapy as a treatment for chronic medial tibial stress syndrome.

Calf strength is another area that needs to be vigorously pursued as a possible prevention and treatment program.  I suspect a successful calf strength program will be fairly rigorous, i.e. not just a dozen half-hearted calf raises every day, but several sets of single-leg raises multiple times a day to rapidly improve strength and endurance.  Popp et al. have proposed that tension from the calf muscles can prevent tibial bending, much like a cable-stayed bridge is held rigid by tension in its supporting wires.13 

Future research should investigate whether calf strength can reduce tibial bending

I would also like to see some research on the use of medially-wedged orthotics as a possible treatment for MTSS.  As I tend to believe Benno Nigg’s34 theories on the function of orthotics in runners, I personally doubt there would be a significant effect in all runners, but it is well worth the investment of a few studies to lay the issue to rest—I’m sure plenty of highly qualified people disagree with my opinion on this.

Lastly, more work should be done on using engineering principles to predict who is likely to suffer a tibial stress injury.  The work of Franklyn et al. is very important because it demonstrates the usefulness of an engineer’s approach to biomechanics: when they treated the tibia like a structural beam supporting a building, they were able to determine what factors were at play in men and women who suffered from MTSS and tibial stress fractures. I hope we see more studies of this nature in the future, perhaps applying the same principles to other stress fracture-prone areas like the metatarsals, the navicular, and the femur. 


First off, if you are suffering from shin splints, don’t panic! The vast majority of cases are mild and recovery quickly.  Understand that the root cause is overloading of your tibia, likely brought about in most runners by a rapid increase in training volume or intensity.  Second, don’t train through it with reckless abandon! Because medial tibial stress syndrome is an injury to the bone, you may risk developing a stress fracture if you continue to train and race with shin pain.  Many runners find that icing their shins is a helpful way to reducing pain, but don’t forget that to fully recover, you need to decrease stress on your tibia and strengthen the bone itself. 

Depending on the severity of your injury, you may need to take a few days or even weeks off to fully recover—remember, your bones are actually weaker for the first month following a significant increase in training.  If you do continue to train, reduce the volume, intensity, and frequency of your runs if you can.  Work with your coach to weigh the risks and benefits, keeping in mind your short-term and long-term goals.  Additionally, work to decrease your impact loading rate by upping your stride frequency by 10% or so, bringing it closer to (or above) 180 steps per minute.  You might also try varying the surfaces you run on to see if a hard, even surface or an uneven natural one is friendlier to your shins.

Both to take stress off the tibia and to encourage it to grow thicker, you should strengthen your calves and the smaller muscles of the lower leg.  While there’s no proven protocol for either of these yet, doing single-leg calf raises (starting with perhaps 3x15 and progressing to 3x30) and Russ Ebbett’s foot drill routine every day are a good place to start.  Supplementing your normal training with some light barefoot running on grass every week may also strengthen your lower leg muscles, and the flatter and more forward landing style you’ll inevitably adopt during these barefoot sessions may load your shins less than when running in shoes.  Additionally, introducing lower-body weight training could strengthen the bones and muscles of your lower leg, increasing their ability to handle the stresses of training.

In the future, consider adopting a training progression which allows some time for your bone to heal, such as taking a “down week” every 3-4 weeks or adopting Jack Daniels’ “equilibrium” model with periodic mileage increases separated by several weeks of even volume. 

If your shin pain localizes to an area under about two inches in size, aches even when you aren’t putting weight on it, or keeps getting progressively worse, you should cease training and see an orthopedist to check for a stress fracture.  While a bone scan is sufficient to accurately diagnose stress fractures, an MRI is the preferred imaging tool because it can give a more precise reading on the severity of the injury and perhaps even provide you with an estimate as to how much time it will take to recover.

A small minority of runners suffer from shin splints on a chronic basis, even with careful monitoring of their training and recovery.  If this is the case, you should consider more aggressive treatments in addition to increasing your cadence and strengthening the muscles of your lower leg.  Over-the-counter orthotics, like SuperFeet Green or PowerStep, are a good place to start, and some distance runners (and other athletes with shin issues, like long jumpers, hurdlers, and sprinters) find that these can help.  True custom orthotics from a good podiatrist are a logical extension of this, and have been shown to help prevent shin splints in military recruits.  Supplementing your diet with 200% of your RDV of calcium and vitamin D is also a relatively low-risk approach that may help with underlying bone issues, especially in women.  Female runners with chronic shin issues should examine their dietary habits and review their menstrual health.  The various factors of the female athlete triad can lead to a whole host of problems beyond medial tibial stress syndrome.

Finally, there are some riskier strategies that, while being theoretically sound from our current understanding of biomechanics, are experimentally untested or carry some risk of additional injury.  Running in firm, thin shoes on a hard surface like asphalt or concrete should (in theory!) reduce stress on the tibia because your overall leg stiffness should drop, transferring stress to the soft tissues of your leg.  Unfortunately, there’s the very real risk of increasing the stress on your metatarsals with this approach,35 so do be conscious of this.

Running in minimal shoes (or none at all) is also likely to promote more of a forefoot/midfoot striking style, which is something you could actively work to develop if so desired.  Like the firm shoes/hard surfaces theory, changing your footstrike style should in theory reduce impact loading on your tibia, but you run a significant risk of injury to the metatarsals, Achilles tendon, and calf muscles while your body adapts to the switch. 

Lastly, depending on the medical practitioners in your area, you may be able to find a doctor willing to try a multi-week course of extracorporeal shockwave therapy if you’ve had long-standing shin problems.  While there aren’t as many risks with this treatment, I’m hesitant to recommend it based off of just one study, especially considering that ESWT is a new and relatively unproven treatment in general.

In all, treatment and prevention of medial tibial stress syndrome needs to take into account that it is a bone injury, not simply an inflammation of soft tissue at the inner edge of the medial tibia.  Therapies, both current and future, should be directed at reducing strain on the shin and increasing the strength and resilience of the tibia itself.  I hope that future research brings us closer to having a solid exercise or therapy program that can successfully treat or prevent shin splints. 


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  1. Isn't the term "Shin Splints" more of a catch-all phrase, and also includes something like chronic exertional compartment syndrome?

  2. This is a brilliant piece of writing. I have a scientific background but have always felt totally illiterate when it comes to life sciences! But I've read two of your articles - the first being the article on scientific terms for anatomical location - which instilled me with so much confidence that I could get a grip on this stuff.

    Now this article. You really should write a book. I'd buy it. It feels such a balanced view... explained scientifically, but in a manner that most (patient) runners would easily grasp.

    I've had one period of getting shin splints... through much of September... as I trained for my first marathon. I'd previously seen that I over-pronated in my right-foot only, whilst having gait-analysis in a running shop. My physiotherapist (physical therapist to you American guys!) found that I had a weakness in a right hip muscle, that was causing my right leg to land at an angle (pointing to half-past-one, if you know what I mean)... and that my right foot over-pronated, presumably as a compensation reaction. It was only my right leg that suffered the shin splints. I've strengthened the hip, and I seem to be OK now.

    I identified with a lot of the article. I particularly noted that Bennett et al had linked over-pronation with MTSS - given that only my right foot over-pronates and only my right shin suffered from MTSS. But I'm sensible enough to know that this is not exactly scientific proof of Bennett's theory!

    I'll bookmark this page, and read it again, to really try and absorb it - in case MTSS ever comes back - though hopefully with the knowledge gained, maybe it won't.

    Thanks again. You should be very proud that your effort is helping so many people.

  3. one specific issue I just picked up on... you say that there are 'worrying' reports of metatarsal injuries associated with wearing Vibrams on hard surfaces. But your reference 30 suggests there are only 2 affected runners in the study.

    I've not read the paper, but do you think it's fair to use the term 'worrying reports' - which sounds quite sinister?

  4. Thanks for the comments! Glad you found the article useful. While you're right that the cited study was only a case report of two patients, a lot of podiatrists are anecdotally reporting seeing "barefoot running injuries" like metatarsal stress fractures:

    Now I know the danger of anecdotal evidence very well, but I think it is something to take note of. Though I'm certainly not in the "barefoot running is the devil" camp either. But it makes sense to me that transitioning to a forefoot striking style and wearing minimally cushioned shoes will stress the metatarsals differently than they are used to being stressed in a traditional running shoe. Even if the overall stress is not GREATER, simply being DIFFERENT may be enough to cause injury—if the shear forces on the bone are in a different direction, or the loading rate is greater, and so on.

    1. Update: more detailed study showing that minimalist shoes increase stress on the metatarsals, at least transiently:

  5. I'm pretty sure your diagram of layers is wrong since there is no Dura or Pia matter in the leg, that is most definitely the skull.

  6. Thanks for pointing that out! I've fixed the image to one that's correct.

  7. No problem, thank YOU for this excellent article.

  8. I'm doing MTSS as a sports case study for my final year at Uni (I'm studying Podiatric Medicine)and 'WOW'!! Awesome article! It's answered all my questions! Thank-you! :-)

  9. Having been unable to walk without pain- or run at all- for the past 13 months due to unnamed and unknown ankle and shin pain (neither of which showed up in any imaging tests), I have read countless articles about running injuries. I have desperately heeded various pieces of advice, some much more logical than others. Nothing has worked yet, but this is the article that has gotten me closest to being able to run again- something two doctors have conceded may be impossible despite the fact that I was only 15 when I got hurt. This is the most detailed, unbiased, factual article I have seen about MTSS. No claims were overstated. The medical world’s lack of definite knowledge on the subject was put out in the open rather than ignored. If I get to prove my doctor wrong by running another season before I graduate, I owe it to The Injury Series and my never-ending stubbornness.

    Some comments I have: while strengthening the calf would be good for the tibia, many people maintain that muscle imbalances are a contributing factor to shin splints; specifically, the calf and its antagonistic shin muscle can become very imbalanced in runners. Russ Ebbett’s six walks, combined with balance exercises, could decrease the likelihood of imbalance issues. About running in hard shoes on hard surfaces, I gave it a shot a number of months ago, about a mile and a half at a time; it resulted in the complete disappearance of my ankle pain, partial disappearance of my shin pain, and- like you said it could- it messed up the metatarsals after 2 weeks. I was forced to return to zero mileage, but I put 9 miles on my shoes over the course of 14 days- the closest I’ve come to a return to running over the last year. Thank you for taking the time to write such helpful, detailed articles. You may never realize the world of difference it can make in the life of somebody you’ll never meet.

  10. This was excellent. Thank you.

  11. Great article! Well written and very comprehensive and informative - thanks!

  12. I've saved this article as a favourite page as it's so helpful both in content and in the way it is written. I used to run years ago whilst part of a contemporary dance company and suffered stress fractures on my shin which eventually healed. I've not done either of those things for many years but have engaged in other activities, as well as had two babies close together, all of which I feel have contributed to having them again because of impact and lack of nutrients/hormones matters. I'll try your recommended exercises but feel reassured just to understand how they happen. Thank you.

  13. Hello, I just posted a thank you for your great article but it hasn't appeared. Maybe you check them first.

    I have had an issue with Pronation and pain in my Tibialis Anterier and tibialis posterior due to overuse. I have put up with only being able to do a single 4km run a week for years. I recently purchased some 3, 4 and 5° wedges to place in my shoes to reduce the pronation. 3 and 4° wedges were not adaquate however the 5° wedge completely removed the pain. However, after continuing my usual one a week 4 km run for three week, I now have MTSS on the front surface of the lower Shin bone in both legs.

    Without the wedge I get tibialis muscle overuse, with the wedge I get MTSS. I'm damned if I do and damned if I don't. Would you have any advise?

  14. Sorry about your first comment! Sometimes the spam filtering software is a little too eager to flag comments it seems.

    Your problem is an interesting one, and it might illustrate a point about biomechanics: shoe inserts can change where forces go in your body, but they can't meaningfully reduce their magnitude. So using the wedges is great because it shifts stress off your muscles, but unfortunately it seems to put more stress on your bones. The first thing that comes to my mind is that you should try to strengthen the muscles that get overworked without the wedges, and also increase the strength of your shin bone. Both of these could take several weeks. If you can make both of these stronger, maybe you can go with an intermediate wedge angle (4 degrees perhaps) and that will even things out, so to speak. Might be worth a shot. Of course this is just my biomechanical conjecturing, a real doctor or physical therapist could do a better job analyzing your specific needs!

  15. For some reason my last reply has me as Helder Monteiro, whoever that is.

    Thanks for the advice, that was my thoughts as well. I am going to try a couple of other changes such as try running on concrete and then explain the results to a specialist.

    I currently run only on grass. On first thought this makes sense as the grass acts as a shock absorber, dampening the peak stress in the bone and muscle and therefore reducing damage.

    However as a Mechanical Engineer I don't think it is that simple. On top of the peak stress that occurs at a specific instantaneous moment during each stride, the total energy (kinetic and potential) that passes through the bone during an entire stride is also an important factor that I think needs considering. (A higher total energy means that stresses are maintained for a longer period of time during each foot strike).

    Due to the dampening nature of the grass (and shoe), a novice runner will bound along injecting huge amounts of energy into the tibia across the entire quarter second foot strike however the peak stress will be acceptable as the dampening spreads the energy across the entire foot strike.

    With the reduction of damping of concrete running, the result is that the energy is more concentrated at the moment of peak stress. A novice would quickly learn that the pain on impact is not healthy and would have no choice but to reduce the bounding (and therefore total energy). The result will be the peak stress on concrete would be the same as the peak stress on grass, however as the bounding and therefore energy in each foot strike has been reduced, the duration of the peak stress would also be reduced.

    In an engineering nutshell, the peak stress causes fatigue damage, and the length of time at any medium-high stress (doesn't have to be peak stress) causes creep damage. So I hypothesize that grass and concrete running cause a similar amount of peak stress fatigue but concrete running reduces time dependent creep.

    Similarly concrete running should reduce the amount of time that the overused muscle has to work for at higher loads.

    Of course, some people don't listen to their body, and just run on concrete like they run on grass anyway.

  16. Just wanted to give you kudos for this brilliant article. Finally a though review of shin splints that makes sense.

  17. Hi John. Can you expand a bit on the paragraph, "Decreasing your training volume..." in terms of making a smart comeback? Should various stretching exercises (flexing feet, calves) be done now or waiting until no pain? Would one not run at all until all pain goes away? Feels like a blunt bruise about 6 - 8" in area about size of palm of hand. I am a 57 year old 23:00 5K hobby jogger. Ran a bit in high school and college, took about 35 years off, then started running again 3 years ago. This is the first running injury the whole time. I thought I had slowly worked my way up to 35 0 40 miles a week this year, but 10 days ago self-diagnosed MTSS. Been cross training for cardio on an Assault (modern version of old Schwinn Airdyne) and something called an Intelli-stride, which is sort of a recumbent stepper / rower, both keep most of weight off my feet. One of my goal races is at end of the month.

    Thank you.

  18. Hi John,

    Great article! I'd like to propose another possibility I didn't see covered which is to ensure the pelvis is allowed to move naturally and not over-stiffened.

    Similar to the other commenters, I am a long time MTSS / medial lower leg tissue/bone sufferer (18 months and counting). All the usual conventional approaches have failed to find any root cause... but to be fair some have been helpful with the symptoms for much faster recovery between runs, particularly full leg soft-tissue rolling, stretches and self massage of medial structures (tib. post and FDL I think).

    To address the root cause I've recently taken a back-to-basics approach, as follows: my medial lower leg hurts because it's overloaded during stance (max. pain). So I would like to find a way to a) reduce peak shock load and b) redirect as much as possible away from medial structures to my calves. The (only!?) advantage of always being in pain when I run is that I can make changes and get instant feedback. In fact for this phase I'm spending significant time either barefoot (2km warm-up) or in racing flats to ensure maximum proprioception and on a treadmill to try and remove as many variables as possible.

    For (a) to minimise shock I need to be using as much of my body as a shock absorber as possible to spread some of the load away from my lower leg. In the course of strengthening the usual running injury muscle culprits and perhaps trying to improve my gait according to mantra of strong core and stable pelvis I now realise I pretty much locked my pelvis up (in spite of using glutes to extend) in a level and static position preventing my pelvis and back from helping to absorb the shock. Consciously relaxing my leg muscles (this is also critical - they still fire when they need to!) and letting my pelvis move "naturally" in all planes of motion including lateral "see-saw" I firmly believe has decreased lower leg peak shock loads. My pain is reduced and my mid-foot strike is noticeably quieter.

    For (b) I'm using the concept of the "foot tripod" and using my newly mobile hips to help direct the initial landing impact to the lateral line of the triangle. This feels magic! It redirects the shock away from my medial structures to my calf muscles in a way orthotics failed to do for me (after an initial benefit). I can start to run pain free in the controlled environment of minimal shoes and a treadmill.

    I'm not saying I've mastered my pelvis use yet, for example in (b) I suspect I'm probably moving my upper body too much laterally to shift my COG closer to the lateral edge of the stance foot rather than allowing only a more subtle shift via my pelvis transverse rotation. It's not yet clear to me if this is a temporary solution to allow me to "run myself out of pain", allow the tissues to heal and strengthen and then go back to a much more subtle shift which may be more economical.

    Whilst my specific issue appears to be with my over-stiffened hips, the reasoning I have used may be more generally applicable e.g.:

    1) Find a way to run quieter (without tip-toeing!)
    2) Find a way to spread the shock through as much of the body as possible
    3) Find a way to redirect the medial forces into the calf muscles

    Sorry for the essay. I hope it might help someone. Any comments on the above most welcome! Thanks again for the great article John.