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Impact forces and how they are affecting your run

Overuse injuries such as Achilles tendinopathy, plantar fasciitis and stress fractures are still very common among the running population, with incidence ranging between 37-79% depending on which research article you read and which population you look at. This is in spite of all of the latest running shoe technologies, expensive insoles, science-based training, and increased awareness of injury risk factors that the running world has seen over the past decade or so.

At ProSport Physiotherapy Huddersfield, we truly believe that these injuries are avoidable if you take the time to thoroughly prepare you body for running. We have already talked about ways in which you can take the pressure off of some commonly over-loaded areas and improve your running economy in previous blog posts, and given practical examples  of how this actually works in-action.

In this blog post we are going to talk about other important factors that are often overlooked and are only starting to become truly recognized as big players in these ever prevalent overuse injuries: impact forces, ground reaction force, and the effect that vibration has on your soft tissues.

Impact forces and ground reaction force – what are they, and why should I care?

As you stand motionless you are exerting force (your body weight) onto the ground. We know from physics and Newtons third law that for every action there is an equal and opposite reaction. That’s essentially what ground reaction force is, the force exerted by the ground on a body in contact with it (you). So if we take running as an example, if your body pushes down and forwards as you heel (or forefoot) strike, the ground reaction force will be up and backwards (see diagram below). Running results in 3-4x body weight in impact forces as the feet make contact with the ground, so the ground reaction force will be equal to this.

Blue arrow indicates direction of impact force from the body onto the ground, green arrow indicates direction of ground reaction force

The way our body perceives these forces is through vibration. This vibration is so important that 80% of the sensory receptors on the plantar surface of our feet are sensitive to it (Pacinian corpuscles). These receptors receive the vibration signals and send information to our brain to determine the compliancy of the surface we are walking or running on. This information is then processed in our sensory cortex with all of the other sensory input our body takes in, an appropriate response is determined, and signals are sent to the different body structures to activate in a certain way to give us the stability we need for locomotion (walking/running) at that time on that surface.

But the vibrations are not always a good thing. Many of the soft tissue structures in our bodies do not like to vibrate, and therefore the stimulus must be dampened as it comes in if we are to avoid irritation and pain in these tissues. To achieve this, our soft tissue compartments must contract isometrically and stiffen at the muscle-tendon junction before our foot hits the floor so that we can load our connective tissues and the vibrations can pass into our fascia. Because the sensory receptors are in the skin on the sole of our feet, the type of footwear we use will alter the way we perceive these forces, and different surfaces such as wood, dirt, and concrete all give out different vibrations, and therefore will require different levels of dampening. If the timing of contraction or dampening is off, injury risk goes way up. To top it all off, these receptors become less efficient as we age!

So what does all of this mean?

It is essential that we keep these receptors stimulated and healthy if we are to avoid these common overuse injuries. The best way to do this is to go barefoot as often as possible. This lets all of the joints in our feet to move, helps strengthen the intrinsic muscles of the feet, and lets these receptors work to their full potential without anything altering the input they receive. Not everyone is suited to minimalist footwear. These are only as good as the feet they are put on, and some people may need some support and cushioning to run or walk any distance, but when you get home it is important to take these off and let your feet breathe. Do some training in your barefeet (even if it is just your prehab!).

Plantar Fascia Treatment Huddersfield

It is also important to consider the surface you are running on. As we said previously, different surfaces vibrate in different ways. For example, wood vibrates very well while concrete hardly vibrates at all. As we said before, your soft tissue compartments need to be contracting before your foot hits the floor to effectively dampen the vibrations coming in. This means your brain needs to be able to predict what level of dampening is needed. Training on the same surface you are going to race on will help your brain get used to this. If you are training on concrete, appreciate that it does not vibrate very well, and therefore your brain can struggle to perceive impact force and ground reaction force (as we perceive these through vibration), and therefore can struggle to dampen what vibrations do result efficiently. This can lead to it passing into muscle tissue and bones instead of our fascia, ultimately leading to injury (e.g. stress fractures). If your race is on concrete then by all means train on concrete, but give yourself an extra day in between runs to let your soft tissues recover (quality over quantity!).

All of this information also supports the use of a specific warm up and prehab routine to keep your body in shape for running. We need to train our brains to be able to predict the amount of dampening that is needed on a particular surface, which we could make more efficient by having a quick walk around bare-foot before warming up in our trainers. We need to make sure our fascial system is supple by including some fascial stretching techniques. We want this fascia to be able to lengthen fully and absorb that vibration to give us the full elastic recoil and spring effect we have talked about in previous blogs. If the fascia is made up of lots of different types of collagen and cross-links from previous injuries, we limit its ability to do this.

Wrap up

Impact forces, ground reaction force and the resultant vibrations are important to appreciate when you are trying to avoid overuse injuries and run efficiently. We are currently updating our knowledge in some cutting edge techniques and approaches to work with these vibratory inputs that we are looking forward to implementing with our patients in 2015. Every body is different and there is never a one size fits all approach, but every little detail is essential if you want to avoid injury. As usual, if you have any questions please contact us via the contact form at the bottom, we look forward to hearing from you!

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  • "Dave is a top class Physiotherapist who has got me back from numerous injuries always weeks earlier than expected. Dave's hands on treatment approach is one of the best I have ever experienced. Highly recommended"

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    Paul O'ConnellMunster Rugby, Ireland and British and Irish Lions
  • “I have seen Dave O’Sullivan on several occasions over the last few years and I have always been 100% satisfied by the work he has done and the exercises and advice he has given. In fact, I am often amazed by the way he can work out what is causing what and how to put it right. Usually only 2 or 3 visits are needed, plus exercises done at home. I completed my first marathon 3 years ago, largely due to his expertise – I could hardly walk a week before race-day. I would definitely recommend Pro Sport Physiotherapy (and have done!)”

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    RobHuddersfield
  • “A 140-mile round trip to visit Dave is well worth it as he’s restored my confidence to overcome injury, using techniques you will probably not encounter elsewhere. Dave’s manner is excellent, taking time to explain things simply and being available to clarify concerns. Many exercises prescribed are provided by video link with is far superior to the dodgy photocopied exercise sheets traditionally supplied as they ensure you can review and perform your rehab using good technique. In my opinion the ProSport experience is years ahead of the game as it adopts the advances being made in its field whereas regular Yellow Pages clincs stick to dated methods. A big plus is that Dave is also interested in getting you right.”

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    ChristopherLincoln
  • “I’d been struggling for the best part of a year with what I (and my old physio) thought was a damaged hamstring. I’d heard about Pro Sport and read about their Soft Tissue Release Techniques and thought I’d nothing to lose by trying a new approach. Thank goodness I did….. Darragh Sheehy correctly identified I actually had a partially trapped Sciatic nerve and set about “releasing” it…. That’s another way of saying pain…..but it really is “no pain, no gain”. After one session I left feeling considerably better. I ran at the weekend with a huge grin on my face……I was thinking “I’m back!” A few sessions later and following Darragh’s exercise regime I’d improved again and within a few months had a new 5k PB.”

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  • “Pro Sport Physiotherapy are amazing! I was having trouble with my hip whilst running over a certain distance. Shane worked out within 15 minutes that a tiny set of muscles near scar tissue was preventing my glute and core from firing. I worked on my exercises for a week and returned to my next appointment to find I was cured. A couple of sessions followed to ease my aching muscles now they were working and I am now fully fit to run my first ever half marathon this autumn. I have recommended the company to anyone who will listen. They are professional, knowledgable, fast workers and friendly. 5 star service with a smile :)”

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    KeeleyHuddersfield
  • “5 years after breaking my leg and 3 surgeries later, Dave O’Sullivan was recommended to me after I received NHS physio where I was told I was a lost cause! Dave’s work is fantastic, I felt an improvement after the first visit and now feel better than ever. He explains everything, follows up the treatment with easy to follow videos and is a nice guy. I wouldn’t hesitate to recommend Dave!”

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