In Part One of this series we looked at the pathology of shin splints and talked about some of the factors that can lead to you being more likely develop the problem.
As we discussed in Part One shin splints comes on when the periosteum of the tibia (shin bone) becomes inflamed. This happens because the repair processes of the bone can’t keep up with the microdamage inflicted by the impact of running. The total impact or total load applied to the tibia depends on how many steps you take and the load per step.
Total Load = Number of Steps x Load per Step
If the total load within a given time (say a week) inflicts more microdamage on the tibia than can be repaired you will begin to experience shin splints. In this article we are going to review some of the running technique factors that will influence the load per step.
Total Load = Number of Steps x Load per Step
When we run we strike the ground with each foot strike. We take the weight on that leg and then we push off again. As we land onto the ground we exert a force into the ground. If you remember your high school physics you will realize that the ground then exerts an equal but opposite force on us. The force that comes back up through us is known as the Ground Reaction Force (GRF).
Researchers who study running injuries have a keen interest in this ground reaction force. They believe it is an important variable in trying to predict those runners who are more likely to get injured. The theory goes that if we absorb this ground reaction force too quickly then the tissues of our body will experience higher internal forces. These higher internal forces mean more load per step. On average, these runners should get injured more often (Davis 2015, Davis 2016).
So, if we don’t absorb the ground reaction force well then the tibia will experience more internal forces. This will cause more strain on the tibia bone and that leads to more microdamage. As discussed in Part One, when microdamage exceeds repair, we get shin splints.
In order to absorb the ground reaction force well we need to cushion the landing. As a quick example just stand up and hop up and down a few times. Now try and keep your knee straight and do it. You will feel a ‘jolt’ when you try and keep the knee straight. That’s because you didn’t cushion the landing. When we bend the knee we absorb that ground reaction force over a longer period of time. It reminds me of jumping out of a tree when I was a kid. Pretty quickly my friends and I learned to ‘drop and roll’ as we landed. We were intuitively absorbing the ground reaction forces over a longer period.
This is where the term Vertical Loading Rate (VLR) comes in. How quickly we absorb that ground reaction force when we land is called the vertical loading rate. Runners with a higher vertical loading rate don’t absorb that force as slowly and thus experience more internal forces in their tibia. I call these “thudding” or “heavy” runners as they make a lot of noise as they run.
Higher vertical loading rates are currently under the microscope in terms of trying to determine if they actually make runners more likely to get injured. A systematic review in 2011 concluded that they do seem to be higher among runners who get stress fractures (Zadpoor 2011). As we discussed in Part One a stress fracture is the end stage version of shin splints.
So if you have shin splints, lowering your vertical loading rate may not be such a bad plan. Then your shin will experience less load per step and you may be able to tolerate more steps.
In 2010 Crowell and Davis conducted a study to see if they could get runners to change their technique and reduce their vertical loading rate. They took 10 runners who had unusually high vertical loading rates and used fancy gadgets to give them real time feedback on it. After a few training sessions they were able to reduce their vertical loading rate by 30% (Crowell & Davis 2010).
Now, we don’t have these fancy gadgets but we do have ears. We can use the amount of noise we make as we run as a proxy for our vertical loading rate. So we’re going to think about trying to run more quietly. Some of the cues I use with runners to try and evoke this change are “run quietly”, “run softly”, “imagine you’re running on hot coals”.
It tends to be easier to work on these things on a treadmill in a quiet room. It’s very difficult to get a sense of how much noise you’re making or how hard you’re hitting the ground when you’re running outside. If you want to read a bit more about these strategies check out my article Am I a Heavy Runner?.
Increase Your Cadence
Running cadence is the number of steps you take per minute as you run. A lower cadence has been proposed as one cause for higher vertical loading rates (Warden 2014). The theory goes that if you increase the number of steps you take each minute each stride will be softer. I dig into the relationship between cadence and higher vertical loading rate in a bit more detail in my article Top Three Running Technique Errors to Avoid. In theory though, if we can increase our cadence by as little as 10% we could reduce our vertical loading rate (Heiderscheit 2010). However, there is some debate on whether this is true (Giandolini 2013).
From a clinical perspective, I’ll often get “heavy runners” to increase their cadence while running on a treadmill. Some will become quieter where some will actually get louder! That little anecdote may help to explain some of the conflicting results that researchers are coming up with. My point here is that the goal is to run softer/quieter. If increasing your cadence achieves this then go for it. If you actually get louder then it may not be such a good idea.
To test this out just jump on a treadmill (ideally in a quiet room) and start running at an easy pace. You can use a metronome app, your GPS watch or some smart phone apps (here and here) to get an idea of your current cadence. Alternatively you can just count the number of steps you take with your left foot in 10 seconds and multiply that number by 12.
Now go ahead and add 10% to that number. Say you run at a current cadence of 160, your goal cadence will be 176. Now you want to try and increase your cadence to 176. You can do this however you like. Some common methods I use in the clinic are to set a metronome to that value and you try and match it with your footsteps. Alternatively you can just think about increasing it and then re-measure your cadence using a device or counting as described above.
Once you have your cadence up to 176 now you have to ask yourself “Am I louder than before?”, “Am I hitting the ground harder?”. You can get a friend to help out or use a phone to record yourself if you’re not sure. Remember, the goal of increasing the cadence in this instance is to “run softer” so you reduce your vertical loading rate. If increasing your cadence doesn’t achieve this, it may not be the best strategy for you.
Consider Switching to a Forefoot or Midfoot Strike
Ok, I’m going to offer a huge qualifier here. I NEVER do this. I honestly don’t think I’ve ever asked someone to deliberately change their footstrike. In my experience it is not such a helpful cue. Loud runners tend to stay loud if the only thing they try to do is change their footstrike. Runners with a low cadence tend to keep their low cadence if the only thing you ask them to do is change their footstrike. Over striding runners tend to keep over striding if the only thing you change is their footstrike.
In short it doesn’t help with any of the other running technique issues that we commonly see. That being said, some have proposed that switching to a forefoot strike may be worth considering in order to help reduce vertical loading rates (Warden 2014). Personally, I think it is more important that we strike the ground gently and underneath our centre of mass as we run. However, I think the jury is still out on whether forefoot, midfoot or rearfoot striking is best overall.
Reduce Running Speed
The magnitude of the load per step depends not only on our running technique, but also our running speed. The faster we run the more load our tibia will experience on each step. I talk about this concept and how it applies to injury rehabilitation a lot more in my article Runner’s Mechanical Load Scale. For our purposes though, we’ll just say that the internal forces experienced by the tibia go down if we run slower.
We can use this as a tool to help up manage shin splints. If you run slower then you may find you are able to do more running overall. Doing this for a while gives the tibia time to adapt to that loading and become stronger. In this way you can use slow running to help you strengthen your tibia and get over your shin splints.
Shin splints occurs when the microdamage in the tibia exceeds the repair. The amount of microdamage is related to the total load experienced by the tibia in a given time frame. The total load is a product of the number of steps we take multiplied by the load per step. The load per step can be reduced by running more softly. Running more softly can be achieved by trying to run quieter, increasing your cadence, adopting a forefoot strike (maybe) and running more slowly.
Changing these things may allow you to run a bit more without pain. The more pain-free running you can do the more the tibia will adapt to that stimulus and get stronger. In this way you can rehabilitate you shin splints.