Saturday, April 7, 2018

What causes metatarsal stress fracture in runners, and how can you prevent it? Research-backed solutions


 Do you have a sharp, aching pain on the top of your foot when you run? If so, it might be a metatarsal stress fracture. The metatarsals are perhaps the most elegant bones in your lower body.

The five long, slender bones extend from your midfoot to your toe joints, and despite their small size, must handle a tremendous amount of stress when you run. As a result, the metatarsal bones are a common location for stress fracture in runners.

If you have pain on the top of your foot or pain in your forefoot, you’ll want to read on. We’ll dig into the scientific research on who gets metatarsal stress fractures, why they happen, how to prevent them, and how you can return to running as quickly as possible.

The basics: Metatarsal anatomy and symptoms of stress fracture



You have five metatarsal bones in your foot. Each one corresponds to a toe, and they are numbered, by convention, starting from the inside. So your first metatarsal corresponds to your big toe, and your fifth metatarsal corresponds to your pinky toe.

When you run, the metatarsals act like a lever, helping you to catapult your body forward by using your forefoot as a base of support. They’re a critical part of allowing your body to use your calf muscles and Achilles tendon to store and generate power when you run. This is why the metatarsals are longer and thicker than their upper-body analogy, the metacarpals on the hand.

Each metatarsal bone has a “base” further up your foot, while its “head” is the rounded part that makes up half of each toe joint. The junction between each metatarsal bone and its corresponding toe is called the metatarsal-phalangeal joint, or MTPJ for short.

Metatarsal stress fractures cause a sharp, localized pain on the top of your foot. Weightbearing, especially in unsupportive shoes or barefoot, will often make the pain worse, and pushing on the top of your foot is usually very painful.

You might get aching or throbbing even when you aren’t putting weight on your foot. Swelling and bruising usually do not occur (if they do, see a doctor ASAP—chances are you have a full-on fracture of a bone in your foot!).

Diagnosis: Is your top of foot pain a stress fracture or tendonitis?


If you are a runner with pain on the top of your foot, the cause is usually one of two things: either a metatarsal stress fracture or tendonitis in one of the extensor tendons that runs along the top of your foot. Fortunately, differentiating between extensor tendonitis and a stress fracture is fairly straightforward.

The extensor tendons of the foot, circled in red. Tendonitis here can be mistaken for metatarsal stress fracture.
Extensor tendonitis, either of the extensor digitorum longus (EDL) or the extensor hallucis longus (EHL) tendons, causes pain along the length of the top of your foot that will be most painful with resisted toe extension and running downhill.

Running uphill or on a soft surface will be less painful, as will running barefoot or in minimalist shoes. This is because these tendons are stressed the greatest just after heel strike, as your entire foot comes into contact with the ground.

Anything that accelerates or accentuates a heel strike, like running shoes with a large heel to toe drop, running downhill, or running on a hard surface, will cause greater pain in the extensor tendons. Even though extensor tendonitis can be painful, it usually does not hurt to push on the top of your foot.

"Lydiard Lacing" can sometimes keep extensor tendonitis at bay
The extensor tendons can also be aggravated simply by lacing up your shoes too tightly. Tying your shoes looser and using a “Lydiard lacing” or “ladder lacing” strategy is occasionally enough to tame mild cases of extensor tendonitis.

The symptoms of metatarsal stress fracture differ markedly from extensor tendonitis. Metatarsal stress fracture often feels worse if you try to run barefoot or in minimalist shoes, and if you push directly on the area that’s sore, you will get a lot of pain.

This isn’t the case with tendonitis. Extensor tendonitis is associated with diffuse pain along the length of the affected tendon, while a metatarsal stress fracture causes localized pain. A stress fracture also has the tendency to ache and throb, even when you aren’t putting weight on it. Tendonitis often feels better as you get warmed up; a stress fracture will feel progressively worse over the course of a run.

Where do metatarsal stress fractures occur?

Metatarsal stress fractures usually occur around the middle of the metatarsal bones, not at the base or at the head. If you do get pain at the head of a metatarsal, it’s more likely an injury to the metatarsal-phalangeal joint.

In terms of their distribution among the five metatarsals of the foot, stress fractures are most common in the second and third metatarsals—these two bones account for 71%of all metatarsal stress fractures.

Stress fractures are far more common in the second and third metatarsals (MT2 & MT3) compared to the rest of the foot. The data above is aggregated from five different studies on military service members and athletes, totaling 403 metatarsal stress fracture cases.1,2,3,4,5
Fourth metatarsal stress fractures are somewhat common, but in contrast, first metatarsal stress fractures are almost unheard of in distance runners.

While it’s possible to get a stress fracture in your fifth metatarsal, these are often associated with an acute rolling or jostling of your ankle—a sharp turn or cutting motion puts tension on the peroneus brevis tendon, which in turn pulls on the base of the fifth metatarsal, causing a fracture, so stress fractures to the fifth metatarsals are more often seen in activities like soccer, basketball, and ballet dancing. 

I should emphasize that all the information in this article does not apply for these kinds of fifth metatarsal stress fractures, sometimes called avulsion fractures or “Jones fractures.” These are deemed high-risk stress fractures because this area has a tendency to heal poorly, so you should be under the close supervision of a doctor when recovering from a fifth metatarsal stress fracture.6

The risk factors and causes of metatarsal stress fracture


Metatarsal stress fractures are the second-most-common type of stress fracture in runners, next to tibial stress fractures.7 They only account for about one percent of all running injuries, but because of their fairly long recovery time (measured on the order of weeks) they can be a pretty devastating injury.

Aside from runners, metatarsal stress fractures are also common among basketball players, ballet dancers, and military recruits. I haven’t encountered direct evidence that women are at higher risk of metatarsal stress fracture, but given that women are 1.5-2 times more likely for any type of stress fracture, it’s highly likely they are at higher risk for metatarsal stress fractures specifically.8

There are very few studies that directly examine risk factors for metatarsal stress fractures in runners; those that do exist are extraordinarily small (sample sizes of 10 people or fewer!) and have contradictory findings. As such, we’ll have to look at circumstantial evidence and use biomechanical analysis to uncover the likely causes of metatarsal stress fracture.

Some indirect experimental evidence does suggest that minimalist shoes increase your risk for a metatarsal stress fracture. A 2013 study conducted out of Brigham Young University followed two groups of runners for 10 weeks.9

One of the groups transitioned carefully to a minimalist shoe (Vibram FiveFingers) while the other group remained in their usual running shoes. The researchers used an MRI machine to capture any evidence of the early stages of stress fractures or top of foot pain in the feet of the runners in the study. They found that 10 of the 19 runners in the Vibram FiveFingers group displayed evidence of bone marrow edema during the study, while zero of the 17 subjects in the control group developed bone marrow edema.

One valid counterargument to this finding is that bone marrow edema on an MRI does not necessarily mean injury is imminent—a different study on Stanford University cross country runners found that 43% of the team had bone marrow edema in their tibia at some point during the season, but none developed any shin pain that season or in the following year.10

However, additional evidence may support a minimalist shoe/metatarsal stress fracture connection. Baseline findings from a cohort study on over 1,200 ultramarathoners found a lower rate of stress fractures in the tibia but a higher rate of stress fractures in the foot among ultramarathoners compared to previous research on road runners.11

The more minimalist design of ultramarathon shoes is one possible explanation for this observation, although the rough terrain and hill climbs involved in ultra running may also play a role.

A shift to forefoot striking is the obvious explanation for why a minimalist shoe would increase your risk of a metatarsal stress fracture. However, the evidence for this hypothesis is similarly circumstantial. Forefoot runners must sustain greater forces underneath their metatarsal heads, so we might expect them to be at greater risk for metatarsal injury.

During forefoot-strike running, there is more force under the forefoot for a greater period during the stance phase, and peak ground reaction forces are higher.12
One computer modeling study suggest that forefoot strikers may experience greater metatarsal stress than rearfoot strikers, as well as a greater increase in metatarsal stress as a function of running speed.13

This suggests that middle distance runners and sprinters would be at particularly high risk because they run fast with a forefoot strike (in minimalist shoes, no less!), but this has yet to be examined in any epidemiological studies that I’ve seen.

Given the massive complexity (and elegance) of the human foot, computational models of the metatarsals during running are still in their infancy.

Nevertheless, models like this one (left), published in 2010, show some agreement with what we empirically observe—substantially greater stress in the second metatarsal compared to the first metatarsal.14


The biomechanical causes of metatarsal stress fracture


The most straightforward cause of metatarsal stress fracture is excessive loading on the metatarsal bones. People in sports that don’t involve heavy loading of the metatarsals—like swimming—don’t get metatarsal stress fractures.

But what’s “excessive”? Plenty of people run 100 miles a week or more, yet don’t suffer stress fracture. Clearly, there’s an interaction between how much you run, the way you run, and the internal structure of your body that determines whether or not you suffer a metatarsal stress fracture.

If you’ve read my articles on tibial stress fracture and medial tibial stress syndrome in runners—the two primary causes of running-related shin-pain—you know that bone geometry plays a major role in determining who suffers a shin injury. This makes sense: thicker, stronger bones are less likely to break, because they can spread out the same force over a greater area.

The distribution of metatarsal stress fractures within the foot gives a clue as to how bone geometry in the foot affects your risk for metatarsal stress fracture. The fact that metatarsal stress fractures are extremely rare in the first metatarsal—by far the largest, strongest, and shortest of the five—strongly suggests that bone geometry plays a significant role in determining injury risk.

The second, third, and fourth metatarsals are longer and skinnier than the first and fifth metatarsals, which partially explains why they are more likely to sustain a stress fracture. The image on the left is from a study of 40 human skeletons; the MRI on the right is from my own foot!15
Data on the relative bone strength of each of the five metatarsals supports this theory. A study on the metatarsal bones of 40 human skeletons by researchers at George Washington University found that the first and fifth metatarsals are the most resistant to bending forces, while the second and the third metatarsals are the least resistant.15 This lines up quite nicely with the observed distribution of metatarsal stress fractures in athletes that we saw in the pie chart earlier.

The correspondence between bone geometry and metatarsal stress fracture rates suggest another potential risk factor—a “Morton’s toe,” the colloquial name for a natural variation in human foot shape where the second metatarsal is significantly longer than the first, which puts the second toe further forward than the rest of the toes.

Because this foot variant is fundamentally rooted in metatarsal length, it suggests that people with a Morton’s toe (also known as a Greek foot) may be more likely to get a second metatarsal stress fracture.

A "Morton's toe" or a "Greek foot" is a normal anatomic variant of the human foot that's caused by a longer-than-average second metatarsal bone. Biomechanical principles suggest that this foot type might make you more likely to get a stress fracture in your second metatarsal—though there's not much you can do about it.
However, bone geometry isn’t the whole story. It doesn’t explain why the fourth metatarsal experiences such a low rate of metatarsal stress fracture compared to the second and third. It’s just as long and slender as the second and third metatarsals, but experiences one third the rate of stress fractures.

We might be able to explain this mystery by looking at the distribution of force underneath the foot. While it makes sense that a skinnier bone would be more susceptible to damage than a thicker bone, that's only true if the applied force is the same.

Studies looking at the distribution of pressure underneath the foot in walking and running find that most of the force weight passes right under the head of the second metatarsal.

The fact that there is less pressure under the fourth metatarsal than the second and third (in most people, at least) might explain why it’s less likely to sustain a stress fracture. Further, it suggests that people who do have a laterally-deviated center of pressure while pushing off the ground (so-called "late supinators") might be at a higher risk for fourth metatarsal stress fractures.

In walking and running, the average location of the pressure underneath your foot (the black line in this image series) passes underneath the first or second metatarsal heads, which might explain why the fourth metatarsal is less likely to sustain a stress fracture, even though it's fairly long and skinny.


Why toes play a role in preventing metatarsal stress fracture


Compared to the rest of your foot, your toes—and the muscles that control them—are stubby and small. The calf muscles, for example, which plantarflex the ankle, are vastly more powerful than the toe flexor muscles. Still, it appears that the toes play an important role when it comes to reducing stress on the metatarsal bones and offloading force from underneath the metatarsal heads during running.

Initial evidence on this front came from studies on metatarsal bone strain in military recruits. Using some creative (albeit painful) methods, researchers in Israel mounted a tiny strain sensor inside a surgical-grade staple, then stapled it into the top side of the second metatarsal bone of a group of Israeli soldiers before a long training march.

Since the strain sensor was fixed to the metatarsal bone in two places, it could accurately measure the amount of deformation the bone sustained throughout the march. The researcher found, perhaps not surprisingly, that metatarsal strain had increased by the end of the march.16 This has implications for runners, too—it indicates that long, fatiguing runs, like those done in preparation for a marathon, are likely to put more stress on your metatarsals.

The really interesting question is why long, tough training sessions increase strain in the metatarsal bones. The best explanation is, believe it or not, toe flexor fatigue. A number of studies support this conclusion:

First, a rather grisly but insightful experiment by Seth Donahue and Neil Sharkey at UC-Davis involved using a mechanical contraption hooked up to a human cadaver foot to simulate the effects of toe flexor fatigue on metatarsal bone strain.17

Like the Israeli researchers, Donohue and Sharkey mounted a sensor to the bone of the cadaver foot so they could measure how much the metatarsal bone deformed under the applied load. When force in the toe flexor tendons was reduced, strain in the second metatarsal increased, and vice versa.

Thanks to cadaver foot experiments, we know that fatigue in the toe flexors leads to increased strain in the metatarsal bones. Because of this, toe flexor muscle fatigue could be a significant contributing factor to metatarsal stress fracture.

Toe flexor strength can offload the metatarsal heads
Long, fatiguing runs also appear to decrease your ability to use your toes to push off the ground. Research across multiple studies shows that, at the end of a long, difficult run (such as a military training march, a marathon, or even a 240-mile ultramarathon), you put more pressure under your forefoot and less pressure under your toes compared with how you run or walk when you’re fresh.18,19,20

A close examination of how the toes and the metatarsal heads interact provides evidence for how toe flexor strength could reduce the load on the metatarsal.

The figure to the left shows how: the toe flexor tendons and muscles push the toe into the ground, creating a reaction force to catapult the body forward. 


The tension from this muscular activity is transferred to the insertion point of the toe flexor muscles, which is on the backside of your fibula. All of this means that less force needs to be applied to the metatarsal head to achieve the same overall force acting on the body. 

However, during a long run or a fatiguing workout, the toe flexor muscles become less able to produce force. Hence, your body shifts force from the toes onto the metatarsal heads, leading to an increase in metatarsal stress.

How strengthening your toes could prevent metatarsal stress fracture


All of the research above implies that strength exercises that target the toe flexor muscles should be included in the rehabilitation program of anyone with a metatarsal stress fracture, and might be worth considering if you know you’re at risk for one.

We’re far from having any clinical trials or scientifically-endorsed exercise programs to increase toe flexor strength, so barring that, we’ll have to do what we always do when faced with scientific uncertainty—revert to what coaches have discovered over many years of working in the real world.

I’ve developed a set of foot strengthening exercises based largely on a set of “foot drills” introduced by chiropractor Russ Ebbets. These exercises are done barefoot on grass or astroturf, ideally, and strengthen the foot muscles in a variety of ways. This is a great place to start if you want to strengthen your toe muscles for preventative reasons.

Barefoot drills for foot strength:


Done barefoot on grass or astroturf. Unless otherwise noted, do 2 sets of each exercise for 20 meters.

*Walking with toes in
*Walking with toes out
*Walking with toes up
*Walking with heels up / Walking with heels up backward
*Walking on inside edge of feet
*Walking on outside edge of feet
*Side shuffle to left and right
*Double-leg hops (30 reps)
*Single leg calf raises (start with 10, progress over time to 30 or more)

Once the weather improves, I’ll be making a video on the foot drill routine—stay tuned for that!

I have found that doing this routine 2-3 times per week is adequate if your goal is to improve your overall foot strength.

All of these exercises are weight-bearing and some of them involve high impact, which makes them great for building bone strength, too, but also makes them a terrible idea if you’ve already got a metatarsal stress fracture that’s causing pain! Instead, you’re better off working on toe flexor strength with more traditional physical therapy-style exercises, like the ones below:

Rehab exercises to increase toe flexor strength:


*Towel crunches with weight on end of towel


Using your toes, curl up a towel with a weight on the opposite end.

*Toe flexion with Thera-band and wooden plank



Using a Thera-Band and a wooden plank, flex your toes against the resistance of the band.

*Standing isometric “arch lift”


While balancing on one foot, use the muscles in your feet to "flex" your arch and flex your toes.


These exercises are all from standard physical therapy programs for increasing toe flexor strength—though I've yet to see any programs specifically for metatarsal stress fracture. 

While there are no set prescriptions on number of repetitions and sets, a good place to start for the toe flexion and towel crunch exercises might be two to three sets of 10-15 repetitions each, progressing in difficulty or number of repetitions over time.

As you might guess, if you are recovering from injury, you shouldn’t do these if they cause pain. Since they are less stressful on the foot, you can do these exercises every day.

How to prevent a metatarsal stress fracture


As with all bone-related injuries, using “down weeks” every 3 to 4 weeks is a scientifically-supported way to allow bone to adapt and strengthen to a new stress. After exposure to a new stress, the body initiates the bone remodeling process. This is a fantastic capability—it’s what allows you to strengthen your bones over time.

However, the first step of this remodeling process involves your body eating away at old bone tissue to make room for new bone cells.

One consequence of this is that your bones are actually weaker for about 3-4 weeks following introduction of a new stress.21 After that, new bone cells start to mature and your bones strengthen again. This is borne out in observations of military recruits at boot camp—most stress fractures don’t occur right away; they occur about a month into the new training program.

 
Here's why I recommend down weeks to prevent bone injuries!
 In the case of metatarsal stress fractures, it’s especially important to recognize that a “new stress” on the bone is not limited just to increased mileage. Transitioning from doing mileage on the roads to doing intervals on the track in racing flats or spikes is another new stress on your metatarsal bones, for two reasons.

The obvious one is that spikes and racing flats tend to make you run with more of a forefoot strike, hence increasing the stress on your metatarsal bones.

Perhaps less obvious is simply the effect of speed. Even independent of footwear, high speed workouts also result in most people transitioning to more of a forefoot striking style, hence increasing metatarsal stress. So, even if your mileage stays the same, consider taking a “down week” from using spikes and flats every 3-4 weeks when ramping up track work.

The foot drill routine outlined in the treatment section earlier is a great way to increase your overall foot strength and prevent the increase in metatarsal bone stress that occurs when your toe flexor muscles get fatigued.

Doing the foot drill routine 3 times per week is a good place to start (assuming you don't currently have a metatarsal stress fracture!).

Some evidence suggests that training in a flexible shoe, like Nike Frees, might increase toe flexor strength.22 However, keep in mind that what we saw earlier—long, challenging workouts in this type of footwear will cause toe flexor fatigue, which will increase stress on the metatarsal bones.

Using highly flexible footwear is best thought of as a training tool to be introduced gradually and used occasionally, rather than a cure-all solution. Too much training in minimalist shoes appears more likely to cause a metatarsal stress fracture than prevent one.

How to treat a metatarsal stress fracture


None of this prevention does a whole lot of good for you right now if you’ve already got a metatarsal stress fracture. The good news is that metatarsal stress fractures tend to heal somewhat faster than other stress fractures, and in most cases, are “low risk”—they heal quite well, excepting the rare case of fifth metatarsal stress fractures.

One review of 320 cases of stress fracture found that metatarsal stress fractures take an average of 7.9 weeks to heal, compared to 11.7 weeks for tibial stress fractures.23 In this study, "recovery" was defined as the time from diagnosis to return to pre-injury activity level (not the amount of time off from any running).

The best method for returning to running following a metatarsal fracture is the same strategy you’d use for other low-risk stress fractures. I outlined this in detail in this article on returning to running after a stress fracture, but it’s worth going over again here.

The first rule is this: if you are having pain when you are walking, you need to be on crutches or in a boot. Pain with walking means that the loading on your body during walking is too great for your bone’s current condition, so you need to take some time off from full weight-bearing. 

An Aircast (left) is the best option, but United Surgical makes a lower-cost cam walker that also works.
The least intrusive way to offload your foot is using a full-sized walking cast, also known as a cam walker, or more colloquially, a "boot." When worn properly, these transfer load from the ground directly to your lower leg, bypassing your foot. This allows you to be fairly mobile without pain.

“Half sized” cam walkers that only go halfway up your leg are not as desirable because there’s less surface area to offload force onto your leg—they really only prevent your ankle from moving.

When I was a coach at Edina High School, we bought a stockpile of full-size United Surgical cam walkers in a range of sizes. For what it’s worth, I (when I was unfortunate enough to need one!) wore a size Medium—I’m 5’10, 140 pounds, and wear a 9.5 D men’s shoe.

We found that the “boots” from United Surgical were the best balance between efficacy and affordability—since we bought something like ten or twelve total, we couldn't’ splurge on the best walking cast for stress fractures.

If you do have the funds, I definitely recommend the Aircast FP cam walker. These use a pneumatic air bladder to increase the amount of off-loading and spread out the load more easily on your lower body, so you get better off-loading and better comfort.

I should emphasize again that the cam walker should be used only until you can walk pain-free again. After that, it's actually harmful to be in a cast—you need to return to normal, pain-free loading so you can stimulate your body to keep repairing bone mass.24

For all cases of stress fracture, it’s wise to review your calcium intake and your vitamin D status. These nutrients are tremendously important when it comes to improving your bone strength, and deficiencies in both are known to contribute to stress fracture risk. 

Given the amount of time most people spend indoors (myself included), it’s virtually impossible to maintain a healthy vitamin D status during the winter months, unless you live somewhere like California or Florida.

Nutrigold Vitamin D3 is my top pick for Vitamin D.

I’m not generally a supplements person, but one of the few things I do recommend to the vast majority of runners is a high-quality vitamin D supplement that provides at least 2000 IU per day. At a minimum, you should take this during the fall, winter, and spring, when it’s too cold to run outside without a shirt on.

I’m currently taking Nutrigold Vitamin D3—one bottle will last you an entire year. If you are a strict vegetarian or vegan, you can opt for DoVitamins Daily D—it’s plant-derived and made with a cellulose capsule instead of a gelatin capsule.

Calcium is an obvious contributor to bone strength, given that’s what bones are made out of. One study in female Navy recruits suggested that a calcium supplement with 400% of your recommended daily intake can decrease the risk of a stress fracture by 25%,25 and research on adolescent girls further supports the importance of calcium intake for bone health.26

It’s not too difficult to get adequate calcium intake through your diet (barring conditions like lactose intolerance, which I happen to have!), but if you are looking for a supplement, the one I recommend is Bluebonnet Calcium Citrate. Note that, while this and other calcium supplements include vitamin D for bone health, the amount is insufficient to get the health and performance benefits of high vitamin D levels.

Calcium plays a critical role in the development of bone strength, especially for girls in their teens. A calcium supplement, combined with vitamin D, may reduce the risk of metatarsal stress fracture.26


How long do you need to be in a walking cast for a metatarsal stress fracture?


Here’s the good news: the days of “six weeks in a cast and call me in the morning” are over. If walking causes pain, the scientific evidence says you should be in a cast—but for the minimum amount of time. 

As soon as you can walk without pain, you should be doing so. The reason, as described in a 2014 article by some of the leading researchers on stress fractures, is that your bone adapts to the load it experiences. So, if you are on crutches or in a boot for too long, you’re actually delaying your healing!26

Usual protocol calls for a week or so in a walking cast, followed by some tentative attempts at normal walking. If these still cause pain, you probably need to be in the boot for another week or two. But the sooner you can work back into walking without pain—which you should do gradually, of course, just like anything else—the better.

You may find that walking in a cam walker or “boot” still causes pain—if this is the case, you need to be on crutches until you’re able to transition to a cam walker. The same principle applies: the sooner you can use a cam walker without pain, the better.

Of course, the above is only the current scientific consensus. These are guidelines, not hard and fast rules. Severe cases of metatarsal stress fracture, or people with poor bone healing, may need much longer in a cast or a boot, so if you have any doubts, ask your doctor (and make sure you’ve found a good doctor).

Returning to running after a metatarsal stress fracture


The same loading principles apply to transitioning from walking (without a boot) to running. Warden et al. recommend that you have five to seven full days of pain-free daily activity—i.e. walking to class, going up staircases, etc.—before you try running again. Your first run back isn’t supposed to be a hard ten-miler either. After a week of no pain is when you can start a return-to-running program.

This first “run” is probably going to be a pretty humble walk/jog routine (see here for some sample programs on returning to running after injury). If things go well, you can return to some semblance of “regular” running within a few weeks of your initial walk-jog bouts.

In the meantime, if you want to maintain your fitness, you should definitely take up a cross-training routine. If possible, I recommend aqua jogging, since it’s the most mechanically similar cross-training you can do while not loading your foot. 

As I've detailed over at RunnersConnect, aquajogging can maintain running fitness for at least six weeks. However, even with aqua jogging, you may find the mere resistance from moving your foot back and forth causes pain if you have a more serious case of metatarsal stress fracture. If so, you’ll need to lay off even from the pool until you have no pain.

Research shows that aquajogging with a flotation belt is more mechanically similar to running, so I always recommend runners wear a flotation belt (albeit the smallest one they can get away with) when they aquajog.

I'm still not in love with any flotation belt brands—the Water Gear Aqua Trim in size small is the perfect amount of flotation for runners, but the belt is too short for many people, and it feels cheaply made.

The Aqua Jogger Pro Plus is very well made, but provides a little too much flotation for skinnier runners. You could always get an Aqua Jogger Pro and lop off some of the foam with a utility knife. Drop me a line if you've got aquajogging belt suggestions!

If you are truly lucky, you may have access to an AlterG Antigravity Treadmill. In my coaching tenure at Edina, we used an AlterG with great success to facilitate a rapid return to running after stress fractures (and even avoided a few by putting runners with early stage bone pain on the AlterG for a week or two).

As you might guess, you'll want to start at a low relative weight (usually we started at 60%) and, over the course of a few weeks, progressively increase your relative weight, always staying below the threshold that causes pain. Once you reach 90 or 95% of body weight, you are ready to move to running outdoors again.

When you do return to running, especially if this isn’t your first metatarsal stress fracture, you might consider a change in footwear. The scientific evidence reviewed above suggests that two types of shoes might be helpful: First, a more traditionally-cushioned shoe seems to cause less stress in the metatarsal bones compared to a minimalist shoe, at least based off the BYU study on minimalist shoes.

Second, because the role of the metatarsals is to act like a fulcrum to catapult your body forward, outsourcing some of this fulcrum behavior to your shoe could take some stress off your metatarsals. Nike’s Zoom Fly incorporates a spring-like plate made of, which runs the length of the sole, so it could work as an ideal shoe for people prone to metatarsal stress fractures.

A Hoka One One shoe, with its thick midsole, may also provide a similar function. It remains to be seen whether other shoe companies follow suit with full-length rigid plates in the soles of their shoe.

Conclusion: Preventing, treating, and recovering from metatarsal stress fracture


If you’ve developed an aching pain or soreness on the top of your foot, you might have a metatarsal stress fracture. This injury can be easily distinguished from extensor tendonitis—the other main cause of top of foot pain—thanks to a few key symptoms. 

Metatarsal stress fractures hurt (usually a lot) when you apply direct pressure to the injured area with your thumb. They tend to get worse as a run progresses, and they will be more painful on uphills and during barefoot walking or running. None of this is true for extensor tendonitis.

Whether you’ve suffered a metatarsal stress fracture or are looking to prevent one, the main risk factor that you can control is the level of stress in the metatarsal bones. Strong circumstantial evidence suggests that strengthening your toe flexor muscles is an excellent place to start, because toe flexor fatigue increases stress on the metatarsals.

Keeping your vitamin D and calcium intake high may reduce your risk as well by helping your body improve bone strength.

Some evidence suggests that a limited amount of training in a flexible shoe could increase your toe flexor strength, but full-time training in minimalist shoes—even when introduced gradually—seems to put you at risk for a metatarsal stress fracture, likely because of the shift to a midfoot or forefoot strike.

A more rigid running shoe that outsources some of the bending stress to your shoe's midsole might reduce stress on your metatarsals.

Biomechanical analysis of metatarsal bone stress suggests that people who are naturally midfoot or forefoot strikers could be at higher risk, as well as people who do faster training. This means sprint and middle-distance runners are particularly at risk. On the other hand, marathon and ultramarathon training may be a problem too, since long, fatiguing runs tend to increase stress on the metatarsals.

As with all bone injuries, taking down weeks every 3-4 weeks is a good idea. Decreasing stress on the metatarsal doesn’t necessarily mean decreasing mileage—it could be a reduction in high-speed training in flats and spikes, for example, or taking more recovery days after a long, hard marathon workout.

If you do suffer a metatarsal stress fracture, you should be in a cam walker or walking cast (i.e. a “boot”) until you can walk pain-free. Once you’ve been able to walk pain-free for a week or so, you’re ready to start a gradual return-to-running program.

While getting a metatarsal stress fracture can be a major setback, the good news is that they do tend to heal more quickly than other stress fractures, meaning you’ll be back on the roads or out on the trails before you know it.

References


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12.       Cavanagh, P. R.; Lafortune, M. A., Ground reaction forces in distance running. Journal of Biomechanics 1980, 13 (5), 397-406.
13.       Li, S.; Zhang, Y.; Gu, Y.; Ren, J., Stress distribution of metatarsals during forefoot strike versus rearfoot strike: A finite element study. Computers in Biology and Medicine 2017, 91, 38-46.
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19.       Rosenbaum, D.; Engl, T.; Nagel, A., Effects of a fatiguing long-distance run on plantar loading during barefoot walking and shod running. Footwear Science 2016, 8 (3), 129-137.
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21.       Beck, B. R., Tibial Stress Injuries-An Aetiological Review for the Purposes of Guiding Management. Sports Medicine 1998, 26 (4), 265-279.
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