This article in the UK Daily mail http://www.dailymail.co.uk/home/moslive/article-1170253/The-painful-truth-trainers-Are-expensive-running-shoes-waste-money.html has an extract of a new book by Christopher McDougall about running shoes and their injury prevention claims and led us to our topic today.
We decided to use video analysis to examine how running shoes affect pronation. We are going to show you how to measure rearfoot pronation using your video camera. This measure is often used in speciality running shoe stores to help customers choose the correct anti-pronation running shoes. We will show you how its done and measure the pronation of an athlete running barefoot and with trail shoes.
Pronation of the foot occurs when the arch of the foot collapses and the foot turns outward. The higher forces incurred with running can force the foot into over-pronation, which is often associated with running injuries. Supination is the opposite of pronation and occurs when the foot turns inward.
Below is some video of both the barefoot and running shoe trials. To film this properly we needed to use a treadmill. It would be very difficult to get a consistent view of the foot and leg if the athlete had been running away from us and getting further away with each step. With the subject on a treadmill we can position our camera correctly on a tripod and know that we will have a consistently good view of the foot that we need for our analysis.
You will note that the camera is set up directly behind the subject and in line with the right foot. For this analysis we will concentrate only on the right foot; we therefore made sure that we had as straight a view as possible of the right foot when it was on the treadmill (it is not important when it is in the swing through as we are measuring pronation during the foot stance).
Another important factor is running speed. we can only properly compare the pronation angle between the two videos if we ensure that the subject runs at the same speed in both videos. With a treadmill this is easy, as we can set running speed. In this case the subject is running at 6 miles per hour in each trial.
Let's look into the detail of these videos by taking some snapshots and comparing the pronation angle at each of three events. We could do a better job of examing pronation by comparing the changing angle vs time throughout the stance (foot on the ground) phase, but we want to do a simple analysis for now and the best way to do this is to pick 2 common time points. Therefore we will compare the pronation angle at first foot strike and mid stance (midway through the foot on the ground stage).
In order to do a proper comparison over various time points or events, it is always better to digitize points. Digitizing is done by identifying anatomical landmarks on the subject such as the bottom of the heel or the top of the Achilles tendon. Many expensive systems exist that use reflective markers to automatically identify points. For our comparison, we used a relatively inexpensive software called MaxTRAQ 2D, developed by our friends at Innovision Systems Inc., and manually digitized the necessary points to calculate rear foot pronation angles.
The runner running barefoot shows little difference in pronation angle between foot strike and mid stance. The measured angles are 178.6 and 178.7 degrees. A measure of 180 degrees would suggest that the foot has no pronation or supination, so 178.6 is showing 1.4 degrees supination (the opposite direction from pronation) which can be ignored. A angle higher than 180 degrees would show pronation.
We then asked our runner to put his shoes on and once again measured the pronation angle at the two stance events.
We can immediately see that our runner shows a little more supination throughout his running stance when he is wearing shoes than when he is barefoot. At foot strike his pronantion angle is 166.1 degrees or 13.9 degrees of supination. At mid stance his foot has come back into an almost neutral position showing only 4.1 degrees supination. Our runner would be considered neutral both in shoes and barefoot.
Our runner is wearing neutral shoes, meaning they do not offer support for pronation or supination. The supination of about 14 degrees seen at heel strike is also relatively small and as we cannot actually see the bottom of the runner's heel through the shoe, we may have estimated this position incorrectly and the foot could be in a different position inside the shoe (most likely closer to neutral).
If we have estimated the heel position correctly and there is slightly more supination when running in shoes, the subject's shoes appear to provide him a level of cushioning which allows him to land comfortably in a slightly unnatural position. Running barefoot can be painful and the runner therefore controls his foot using the muscles and ligaments surrounding the foot. In this way he can avoid pain and injury while running. There is no large difference in our trials though, and our runner does not pronate or supinate too much during his stance phase of running.
We are not all Abebe Bikele (the 1960 Olympic Marathon winner ran barefoot) and we believe the running shoe has more than likely prevented many more injuries than it has caused. Now that you know how to analyze rearfoot pronation, you can buy your next pair of running shoes with confidence and understanding.
If you would like more information on the software we used to digitize these running trials please email us. Also please comment on our post; we love to hear your opinions.
Posts
7 comments:
Interesting analysis guys! I found it very informative. My only criticism is that the video clips are way too short --1 sec. They are over before they start it seems. How about a few loops?
Its not really surprising that after running in shoes for years that someone runs similarly without shoes. Try comparing somebody who has learned to run without shoes to somebody who has learned to run with shoes and you'll have a better comparison. Also, the cushion of the treadmill allows the runner to depend on that instead of using their feet's natural ability to absorb shock. Try running over hard packed ground and you might get a different result.
Thanks for your comments and suggestions.
Our subject here is neutral (no pronation or supination) and therefore studying the effects of the shoe on his pronation was not likely to yield any definitive result. If we had collected information from a force plate, research suggests that the impact forces would have been higher when running with shoes. The treadmill may provide some cushioning, but the act of running barefoot encourages the runner to place their feet with more control and therefore reduce the impact forces. This is a study for another time.
Landing heel first while barefoot negates the point of running barefoot doesn't it? or am i missing something?
Barefoot running encourages the runner to midfoot or forefoot strike rather than heel strike. In this article we were discussing the rear foot pronation angle and whether it differs between running in shoes and barefoot. The runner is asked to run and feel comfortable and not specifically to avoid heel contact. We also do not have a side on camera and therefore cannot properly evaluate whether our runner is heel striking or midfoot striking. Our still image for barefoot is at a point just prior to foot strike (as our frame rate was a slow 30 fps)and it appears as if he is heel striking, but on watching the video slow motion and comparing it to the shod running video, we believe this runner is landing more toward his mid foot when barefoot running than on his heel.
This is not really an evaluation of barefoot running because the person in the video is accustomed to running in shoes, and is then asked to run on a soft surface. To analyze barefoot running you would need to get a person who had become accustomed to running on hard surfaces (roads) in bare feet. They would have a very different gait.
If you are not sure what I am getting at, take your shoes off and try running a few kilometers on a road. You will soon see that you automatically produce a very different gait. (You would not notice this on a treadmill.) What is more, after a few months of training, your gait would have become even more different, as the muscles in your calves and feet develop.
At that point a comparison with a shod runner would become meaningful.
This is a good analysis for running barefoot and with shoes...I learned a lot in this post...Thanks!!!
vibram
Post a Comment