Shin Splints – What You Need to Know
Shin splints (technically called “Medial Tibial Stress Syndrome, or MTSS) is a very common injury in runners. I see a lot of runners with this injury and the vast majority of them are relatively new to running.
The first thing we need to understand about MTSS is that it is a bone injury. It used to be thought that the pain was on the periosteum of the bone (the most outer layer) because the muscles of the leg underwent tiny tears where the attach to the bone. For the most part, that idea has been shown to not be true. Newer and better imaging has shown that the injury is in fact, the bone itself [references here, here, here and here]. In other words, a bony overload injury. Under normal circumstances, the strain of running causes microdamage in the bone which leads to an adaptation process to strengthen the bone. When the damage exceeds the ability to lay done new bone, localized areas of osteopenia result (osteopenia is a reduced bone density).
So, when people talk about shin splints vs. stress fractures of the tibia, they are essentially the same injury but with greatly varying degrees. Shin splints are localized areas of osteopenia and bone growth activity, a “stress reaction” is a bit worse and it’s when the bone marrow begins to have edema (swelling) and then finally, you get a stress fracture where there are actual fracture lines present in the cortex of the bone as seen on the MRI/CT. So, they are different stages of the same cause – overloading of the tibia with an inability of the bone repair to keep up with the stress applied to it.
There are two approaches to dealing with MTSS, and they both should be followed: 1) Reducing the load on the bone and 2) Increasing the bone strength.
Reducing the load on the bone:
There are a few risk factors for MTSS. Some are well established some are not. Some previously cited risk factors include “over”pronation, high BMI (Body Mass Index), leg length inequalities, low calf strength, less experienced runners, high load/loading rate, use of orthotics, poor motor control in the hip, poor bone mineral density and some others that I’m not going to get into. So, let’s briefly look at some and look at others in more detail:
This has been a term that is thrown around without much thought. Unfortunately, we can’t even agree on what “normal” pronation is, and f we can’t figure out what normal is, how do we know what “overpronation is? I made a lengthy blog post about this that you can read about here. Studies on whether or not “over”pronation causes MTSS are mixed.
Most of the studies linking excessive pronation with MTSS are researched by using subjects who are currently suffering from MTSS. The problem with that research method is that you don’t know if they are “over”pronating because they are already injured or if the “over”pronation caused the injury (i.e. is it a cause or effect).
Alternatively, prospective studies can be performed in which researchers measure the variables and then track the athletes for a period of time to see who gets injured. In these prospective studies, some studies found that pronation or foot type was not associated with MTSS (here, here and here), while other studies did find a relationship (here, here and here). To further complicate matters, another study argued that it’s not the amount of pronation that we should be looking at, but rather the timing of the pronation that is a risk factor for MTSS.
I have argued in previous posts (here and here) that evaluating pronation is not only unreliable, but there are many proximal factors (higher up in the kinetic chain) that may contribute to pronation. Ankle dorsiflexion mobility and poor motor control in the hip are two factors that can increase pronation significantly.
If control of the hip is not syncronyzed with pronation and supination, there may be some longitudinal twisting of the tibia, since the tibia is between the foot and the hip. There are a few studies that reinforce that hypothesis as they have linked poor motor control at the hip directly to MTSS (here here and here). So, if you are concerned that you may be pronating too much, I would suggest you go have yourself evaluated by someone who understands anatomy, running mechanics and injures to see exactly “why” you are pronating too much (if you even are). Consulting with a health professional who merely applies ultrasound or some electricity on the skin over the area where it hurts is most likely missing the underlying cause.
ii) Leg Length Inequality.
This topic is a bit of a pet peeve of mine. There is extremely poor reliability in measuring leg length and the research suggests that the difference in leg length has to be substantial before there is any meaningful compensation. You can read more about my feelings on it here. Frankly, I don’t really care if someone has a minor leg length difference. I find it of little value. Again, please read why I feel that way here
iii) Low calf strength.
This is a factor that has been shown to correlate to MTSS in a few different studies. It has been correlated with increased tibial stress fractures here, smaller calf girth has been correlated to MTSS here, poor calf muscle endurance has been correlated to MTSS here , and it’s likely because the calf muscles can absorb the shock of landing better than the bone – here. So, starting a calf muscle strengthening program would probably be a good idea in most people suffering from MTSS. I don’t think there is anything to be lost by doing some strengthening work, some power work and some endurance work on the calves. At worst, you have done some extra exercising.
iv) Loading Rate.
Loading is synonymous with force. Research does not support the idea that the “peak amount” of force applied during midstance of running is associated with injury, but research does suggest that loading “rate” is associated with some injuries. The “rate” of loading is the amount of load applied vs time. In other words, how fast the load is applied. If we look at the video below, you can see there is a graph in the video. It is load on the vertical axis and time on the horizontal axis. If the slope of the curve is steep, that means you are applying a load under a shorter period of time (i.e quicker) which is a higher “rate” of loading.
This is very important for MTSS and tibial stress fractures. A) Hreljac et al., did a study looking at runners with recurrent injuries vs. runners who had been injury free through their careers. The only biomechanical variables they found that were significantly different were peak impact force and impact loading rate. B) Irene Davis did a prospective study (here) where they followed 242 runners for 2 years. Before they followed them for the 2 years, they measured different variables. Over the 2 years, 57% of them sustained an injury including iliotibial band syndrome, anterior knee pain, tibial stress syndrome and plantar fasciitis. Statistically significant differences included average vertical loading rate and tibial shock values. They stated, “Based upon the odds ratio for VALR (vertical average loading rate), reducing impacts is likely to result in an overall reduction of injury risk.” C) Last year, Bredeweg et al., did a prospective study by measuring variables and then following the runners for 9 weeks (too short if you ask me). There were 203 runners and they found that amongst the males, the injured runners had higher loading rates and shorter ground contact time.
Loading rate can be changed in many runners by increasing cadence and/or being instructed to “run quietly” or “run softer”. For the most part, I have found these strategies to be effective in runners suffering from MTSS or tibial stress fractures. A 2010 study gave runners verbal instructions to “run softer” as well as providing them with visual real-time feedback for reducing the loading rate and there was good success (although the study only had 5 subjects). A 2012 study used 3 different interventions to try to reduce loading rates: increase cadence, use a racing flat or land with a midfoot strike. They discovered that landing with a midfoot strike was the most effective method at reducing loading rate, however, the study only included 9 individuals and the average cadence was 172, which is unusually high for recreational runners, so increasing cadence may not have had as much of an effect on these subjects as it would on someone with a lower cadence. In order to avoid getting too winded on this topic, if you are still interested in reducing the loading rate, Greg Lehman did a nice post on the topic which you can read here.
The topic of shoes often comes up when talking about shin splints. There is a theory that by going with a minimalist shoe, your body will inherently reduce it’s stiffness in order to absorb the shock that the shoe isn’t absorbing. The theory is based on a few jumping tests where they had subjects jump off platforms and land on concrete surfaces or very soft surfaces. When landing on the harder surface, the subjects increased the knee, hip and ankle bending when they landed in order to absorb the shock (they decreased their leg stiffness). When landing on softer surfaces, the subjects increased their leg stiffness. This is thought to translate into running, but it hasn’t really worked out that way. These studies did not find that [here and here]. In addition, some people simply don’t change their leg stiffness regardless of the shoe type. So, if the name of the game is to reduce the loading rate, some people may benefit from going to an ultrasoft shoe, such as the Hoka line of shoes. Personally, I believe they can reduce the loading rate as long as the body mechanics are also helping to reduce the loading rate. This is supported by some research showing that a shoe can reduce loading rates if the running mechanics are the same [here]. The topic is still a contentious one, however, since there are many studies showing that going with No shoes significantly reduces the loading rates, if done properly. “Most” runners will adopt a forefoot strike, increase cadence and reduce loading rates when going barefoot, but this is not always the case. We are all individuals, and we never know how everyone will react. I recently made a post on that very topic when discussing shoe selection, which you can find here.
v) Use of Foot Orthoses.
OK, we are STILL kind of on the topic of loading rate. This is because the foot’s ability to pronate is a major shock absorber for the body. By using orthotics, you take that ability away. There are a few studies that show orthoses HELP MTSS, but there are also a few that say it HURTS MTSS. I think it depends on the cause. You need to absorb shock somewhere, but your ability to absorb shock in your feet may be reduced if you are using most foot orthoses. This study found that 53% of 146 collegiate runners wearing orthoses developed MTSS compared to 21% of those NOT using them. Most orthoses are designed to limit pronation, but this study and this study say pronation is NOT correlated to MTSS, so, the orthoses thing is really up in the air. in my opinion.
Increasing the Strength of the Bone
i) Gradually Increase Mileage
When a bone undergoes some stress, it needs time to build back up. Studies show that after you start increasing stress to a bone, it takes about 30-45 days to get building up it’s strength. That means that when you initially start a running program, there is a period of 1-2 months where the bone is being broken down by the stress and it hasn’t had time to build itself back up yet (see here]. That is a significant amount of time when the bone is MORE vulnerable to injury. Therefore we need to take a very slow approach to training. I typically use this program from Blaise Duboise to get runners back into running after a serious injury. I know it seems very elementary, but it makes sense to take a couple months to slowly build up bone strength.
ii) Manage Your Pace
In addition to running frequently in brief periods, pace is also important, since loading rate increases with increasing pace. My experience has had good success for those with MTSS to start training under aerobic threshold until their bones have built enough strength to add in speed work or tempo runs. You can read more about training slower and building a proper aerobic base here
iii) Evaluate the Health of Your Bones
For those who just can’t ever seem to get over the MTSS, I’d suggest you consult with an orthopedist or endocrinologist and get a bone density test and blood work to test testosterone, parathyroid, calcium, vitamin D levels and whatever he thinks might be necessary. Since MTSS is characterized by localized bone loss, I don’t think it’s unreasonable to consult with an MD about your bone health. There are many factors that could find out why you are vulnerable to bone injury.
In summary, MTSS is a bone injury with many possible biomechanical or physiological roots. Evaluation of overall running mechanics including leg stiffness, cadence and motor control in the hip are important Interventions such as gradually increasing mileage and pace as well as performing some calf strengthening are also important. Assessing your bone health through blood work and imaging may be necessary for some individuals who suffer from recurrences.
Having yourself evaluated properly is vital to understanding why you are having the injury and also how to correct the problem.