Shin Splints: How Improved Running Form Lowers Impact Forces

"How do I get rid of this annoying ache in the front of my shin when I run?"


Shin splints plague runners of all ages and ability levels.   Shin pain accounts for 5-17% of all running related injuries.  

Anterior shin pain can be dull and frustrating to sharp and debilitating limiting running mileage or running altogether.  Research has demonstrated some risk factors associated with a higher risk of developing shin pain while running.  A meta-analysis of literature related to medial tibial stress syndrome (shin splints) noted these following risk factors:

1. Increased hip external rotation in males
2. Female gender
3. Increased body mass index (BMI)
4. Lower running experience (novice)
5. Navicular drop
6. Usage of orthotics
7. Previous history of medial tibial stress syndrome In addition to these factors, increased vertical ground reaction forces and impact peak forces have been linked to a higher risk of stress fractures.  Although medial tibial stress syndrome was traditionally thought to be a muscular injury, prolonged stress and unchanged loading during running, from altered biomechanics, create bone irritation and injury. 

Looking at the above risk factors, there are clearly some that can and can't be changed. Many have written about shoe choice, slowly progressing running mileage, running on compliant running surfaces (although this may actually make the problem worse), stretching, and of course the dreaded rest.   Yes, if there is risk of bone injury, as in the case of a stress reaction or stress fracture, a period of rest is beneficial and will aid recovery; however, often times rest is seen as "the cure" instead of a "initial phase" of the cure. Recently, in the field of running biomechanics, there has been more in-depth analysis of loading forces and lower extremity joint angles and their relationship to overuse injuries.  Luckily, running biomechanics CAN be improved and this article will provide a specific example of how reducing vertical impact loads made a huge difference in one triathlete's ability to run without pain.

Shin Splints: Vertical Impact Loads

Running is comprised of both a forward progression of the body and vertical movement component.  Right after the float phase of running, when both feet are off the ground, your body will fall towards the ground onto one leg.  The amount of force calculated during single leg loading in running is between 2.5 and 5x your body weight.

Any altered alignment or inability of the body to absorb this shock will result in overuse and eventual injury.  In the case of shin splints, increased vertical loading places greater muscular demand on the front and side shin muscles and also on the tibia (shin bone) itself.  When the muscular anatomy can't handle the strain due to high forces the passive anatomy (bones) take over.

Initial injury to the bone takes place in the outer layer of the bone called the periosteum, a layer of dense connective tissue that covers the bone, and as loads progress can further injure the underlying bone itself.  The progression of shin splints when untreated and volume/intensity remains the same and looks something like this:

1.  Anterior/Medial Shin Muscle Strain
2.  Chronic Shin Muscle Strain (Medial tibial stress syndrome)
3.  Tibial Periosteum Irritation/Injury
4.  Stress Reaction (precursor to fracture seen via x-ray and bone scan)
5.  Stress Fracture

The key here is to improve the biomechanical running faults leading to higher vertical loading rates and tissue injury.  

Now let's take a look at a specific example of a triathlete with a chronic history of shin pain and how improved biomechanics and shock absorption allowed her to run again with little to no pain. 

Chronic Shin Splints: Improving Impact Forces 

Graph of Vertical Impact Forces At Initial Assessment of Triathlete With Chronic Shin Pain

Vertical impact forces are a key variable to test and track in runners with shin splints. The above graph is a real example of a triathlete who attended a running gait analysis and our gait lab here at Competitive EDGE Physical Therapy in San Jose.

During our initial testing we observed a high impact peak pressure of 1040N.  The impact peak occurs during the loading response phase of running gait just after initial contact and before peak knee flexion.   Additionally, we observed the impact peak pressure was almost as intense as the peak loading value.   This finding suggests a sharp and quick increase in loading at the beginning of gait versus as steady loading rate.  Ideally, we would observe a pressure graph that has a steady slope up to peak loading which would indicate proper active muscle shock absorption.

This picture shows the moment of impact peak where the 1040N of pressure was observed.

This is a heel strike runner who also exhibited limited knee flexion at initial contact and an upright trunk posture. These are biomechanical factors that also contribute to high impact and vertical loading forces.

Here we see her knee flexion angle at impact peak was 19.9 degrees.  Later we will compare a still image from her final running test at impact peak.

Image of Impact Peak During Running Gait Analysis

So, why is a large impact peak pressure harmful?

Bone, by nature, is capable of handling large loads since it has the help of the muscular anatomy and the bone itself will tolerate small amounts of deformation while rebuilding following strain.  Once the intensity of load and quickness of loading increase the bone can no longer rebuild fast enough to keep up.  Simply put, the bone builders can't work fast enough to match the speed of bone deformation and injury from high loading rates.

A steady rate of loading and lower impact peak pressure allow healthy bone to rebuild and provide strength and stability to a repetitive force such as running. 

Wearing heavily cushioned shoes may dampen some of the impact force but it will not change the rate of loading.  Rate of loading is affected by running biomechanics, strength, and motor control of the lower quarter.

Running Form Changes To Decrease Loading Rates And Ease Shin Splints

One key running form parameter I track and observe in runners with high loading rates and impact peak pressures is knee flexion angle at initial contact.

By now you have likely read a running article that talks about over-striding.  Although this topic hasn't extensively been studied in literature, there is plenty of evidence of how it negatively affects running.  Over-striding occurs when you initial contact point of your foot on the ground lands well in front of the mid line of your body.  Ideally, your foot should land close to your center of mass when it first contacts the ground.

When you observe over-striding it is almost always accompanied by limited flexion at the knee.  Basically, the knee will be close to fully extended at initial contact. Depending on the statistics you read, the knee flexion angle at initial contact should fall somewhere between 20-25 degrees.

Let's take another look at the triathlete with shin pain and her improvement in knee flexion at initial contact during her training.  

 

Changes in knee flexion angle from running re-training using real-time knee angle and pressure feedback

Through the course of training, this athlete was able to increase her knee flexion angle by 13 degrees which had a substantial impact on her peak loading pressure and overall loading. 

The graph below shows the pressure graph from her final running assessment at the end of running re-training.

Post-Training pressure graph: Running analysis showing impact peak and peak loading As you can see, the graph above showing post-training data looks quite different from her initial loading graph.  In particular there is a substantial decrease in impact peak pressure and a decrease in peak loading.  Additionally, the rate of loading, or slope of pressure line, is decreased as well.  

Here is the direct comparison for you:  62% reduction in impact peak forces and 14% reduction in overall peak loading. 

Using real-time running feedback of knee flexion angle and landing pressure this triathlete greatly reduced the load on her tibia and shin muscles and is now running with a 95-100% reduction in shin pain.

Strength training for the gluteal muscles, quadriceps, and calf also helped to improve eccentric loading control.

In this specific case, knee flexion angle was a key variable but that does not mean that is the only variable that can make a positive difference in shock absorption. Other resources report increasing trunk flexion (forward lean) helps to take pressure off the anterior leg structures (quads and shin) and place more work on the gluteal muscles.

Transitioning to a mid-foot or forefoot running style has also demonstrated improved impact peak shock absorption although this is at the cost of greater demand of work at the calf muscles. Real-Time Pressure Feedback: Shin Splints If you are a runner or triathlete dealing with shin splints it is important to consider the biomechanical forces affecting your body.  New shoes, stretching, and altering running volume and intensity can all help initially to decrease pain.  No runner wants to take time off to rest.  If you are looking to improve your running form, decrease your impact peak and peak loading pressures, and run long term with decrease injury risk...check out getting a running analysis that can track this type of data and help you re-train your form.

A comprehensive running analysis with pressure and real-time angle data helped this triathlete have a successful racing season.  If you have tried everything else with minimal progress, call your local physical therapy running specialist and improve your form!

Written By:  Kevin Vandi DPT, OCS, CSCS

Serving San Jose, Campbell, Los Gatos, Almaden, Bay Area
 

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