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Shin splints biomechanics

 

This is usually the most mis understood part of any shin splints problem. Most athletes and even some medical professionals do not understand the underlying faulty mechanics that can lead to shin splints. In this section we will attempt to describe as simple as possible the subject of biomechanics and how it can cause shin splints

Biomechanics an overview

The term biomechanics refers to the way our muscles, bones, and joints work together as we move. When applied to the lower limb, we focus on the biomechanics of impact absorbtion and propulsion.

The gait cycle

The gait cycle is sometimes called the walking (or running) cycle. The gait cycle extends from heel strike to heel strike of one leg and includes the stance and swing phases of both legs.

In the basic gait cycle the movements are divided into the times when the foot is on the ground (the stance phase which takes up 62% of the full gait cycle) and when the foot is off the ground (the swing phase which takes up the remaining 38% of one full gait cycle).

the gait cycle

The stance phase of gait can divided into the point of initial contact of the foot on to the ground (heel strike HS), the point when the full foot is on the ground (mid stance) and the point where the the stance phase ends (toe off TO).

Take a look at the walking and running cycle here.


Note: There are times when both feet are on the ground and times when only one foot is on the ground.

Double limb support occurs when both feet are on the ground and single limb support when only one limb is on the ground.

Double limb support occurs for two periods of 12% of the gait cycle in a normal walk. Double limb support occurs between heel strike of the limb and toe off of the contralateral limb. In general, as walking speed increases double support time is reduced until it is eliminated and the gait changes to running. During running the gait cycle for each leg is composed of a single support phase and a float or airborne phase.

Single limb support occurs for two periods of 38% of the gait cycle in a normal walk.

To summarise the stance phase of gait can be divided into three periods:

 

 

heelstrike Contact period or heel strike. This is the beginning portion of the walking or running cycle. The foot usually strikes the foot with the heel first with the foot angled inwards slightly so that the heel strikes the ground on its outside edge. This is caused by slight invesion of the ankle at first contact phase.

 

midstance

 

The mid-stance period of the stance phase when the foot is flat on the ground moving on to heel lift.

 

toeoff

 

The propulsive period of the stance phase when the heel is lifted off the ground and the toe off position is taken.

 

 

 

Biomechanical causes of shin splints

Now we understand the simple biomechanics of the lower leg and foot whilst running and walking it is easier to comprehend what negative biomechanical forces can cause shin splints.

 

Biomechanical cause 1 - Over pronation or the flexible flat foot


Just after the heel strikes the ground when running the foot begins to pronate. Pronation is a movement that occurs as the weight of the runner moves from the lateral aspect (or outside) of the heel to the medial aspect (or inside) of the forefoot. This movement allows the foot and leg to adapt to the terrain and absorb the impact of the footstrike. A certain amount of pronation is necessary to run normally but too much or too little can contribute to injuries. Runners with low arches tend to "over-pronate".

When the foot is in an over-pronated position the alignment of three major joints in the foot are less than optimal. This misalignment of the joints causes the foot to become structurally unstable, and, in turn, the muscles, tendons and ligaments of the lower leg are forced to work harder in an attempt to stabilise the foot. With shin splints the thats control the foot and ankle deceleration have to work harder at heel strike midstance AND toe off. This muscles include posterior tibialis and tibialis anterior.

If tibialis anterior has to work harder, anterior shin splints can occur.

If tibialis posterior has to work harder posterior shin splints can occur

 

video of over pronation whilst running

 

 

 

Athletes beware!

Overpronation is the most widely understood cause of shin splints but it is not the only cause. This is where a lot of athletes and medical professionals alike go wrong. Whilst over pronation can cause shin splints, altering the mechanics to stop pronation when this is not the underlying mechanical problem can be disasterous.

 

Biomechanical cause 2 - Under pronation causing early heel lift (the rigid foot)

The term under pronation is not an accurate one but it is easy for the non professional to understand. The term used by professionals is supination but again this is not entirely accurate as very rarely will you see a true supinated foot at midstance in the healthy individual.

The most accurate way to describe the second biomechanical cause is is that of a rigid foot type. A rigid or high arched foot causes the individual to have an early heel lift during the gait cycle. The runner who has a rigid foot will often be observed running on their toes and would be classed as a "toe runner" by their peers.

 

rigidThis picture whilst slightly out of context shows what a rigid foot type looks like when none weightbearing. See how the front of the foot is markedly lower than the heel? During the gait cycle this means that as the forefoot is already lower than the heel, the time it takes for the forefoot to strike the ground is reduced. When the forefoot makes contact with the ground mechanics states that the foot will start to stiffen up ready for toe off phase of gait. With a rigid foot type this occurs earlier and leads to early heel lift.

 

video of under pronation whilst running

 

 

Patients with a rigid foot type can suffer from all three types of shin splints just like the over pronator.

Posterior shin splints. The tibialis posterior muscle does not only act to slow the foot down at heel strike but also works to stop over pull of the achilles tendon when in the toe off phase. Therefore if the athlete has a rigid foot type then they can be at risk of shin splints.

Anterior shin splints. Tibialis anterior also has to work harder with a rigid foot type as one of its roles is to stop the forefoot from catching on the ground during the swing phase of gait. If the forefoot is lower than the heel the the risk of it catching are greater so tibialis anterior has to pull to stop this from occuring.

Bone shin splints are also a problem for the rigid foot type, more so than with and over pronator as whilst it is an efficient foot type to have, it is a poor shock abosorber. Shock is transferred from the foot to the lower leg causing micro trauma.

Athletes beware 2!!

It cannot be over emphasised enough that often athletes are mis-diagnosed as being over pronators when what is actually happening is normal compensatory pronation. This causes the athletes frustration in time, money and delay in getting back into sporting activity. If you have bought anti pronatory trainers and been given anti pronatory orthotics and initially noticed an improvement but then started to get worse, then it is likely that you fall into this category. Further bioemechanical assessment and consultation is advised.

Our clinics are located in Manchester and may mean a bit of travelling but it could prove beneficial. Visit our personal clinic pages for information regarding a consultation.

 

Other biomechanical causes include:

  • Poor running mechanics;
  • Tight, stiff muscles in the lower leg;
  • Running with excessive forward lean;
  • Running with excessive backwards lean;
  • Landing on the balls of your foot; and
  • Running with your toes pointed outwards.

 

How do I know if I'm an over-pronator or an under-pronator?

 


The most common method a runner can use to determine what foot type they have is to stand on a paper towel with a wet foot. If your foot leaves an imprint of your entire foot, from heel to toe, you probably have a flat foot. If the imprint consists of the heel, the ball and a thin line connecting the two, you probably have a high-arched or supinated foot. This method is accurate if you have an extremely flat foot or an extremely high arch, but is not very accurate for those of us who fall somewhere in between.

 

Think you require treatment for your shin splints symptoms?

Visit our sports podiatry clinic pages for a clinic near you.