Foot Physics

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The human foot is apparently one of the most misunderstood mechanisms in the running community, which is incredibly unfortunate. For years, shoes have been viewed as tools to correct the bio-mechanical inefficiencies of your feet. Stores will sell you shoes with “motion control” or “stability” or “neutral” characteristics. All of which refers simply refers to the amount of limitation imposed by the shoe on your foot. So, let’s think about this. Two of the most important body parts for running are your left foot and your right foot. Why would anyone want to limit their motion in any way?

According to the book, “Born to Run,” running shoes used to be very minimal until Phil Knight, creator of Nike, decided to add extra padding to the heel. Knight’s hypothesis was that, with a padded heel, a runner could lengthen his stride, cover more ground with each step, and would effectively finish faster. Whether this worked or not has been lost in the years and years of shoe companies interfering with our natural running form. I won’t go off on how marketers design running shoes and running stores will sell you the idea of a shoe that can make you faster or better. I will just say that if you want to fix your running form, take off your shoes. Here’s how I used to run and how many of us picture a standard running form (if we were stick figures):

Bad Form

If I was a shoe company and thought this was the way people ran, I too would see the foot as being in the way. The point of contact above is the heel and the foot is used to pull the body over the knee so that the other heel can strike.

Now, I was compelled by the barefoot running craze. I found out the hard way to ease into long distances in a minimalist shoe. That, if you change your form to a more midfoot / forefoot strike, you should just start your training program over at the beginning. I trained and completed three marathons in Vibram Five Fingers. I also fractured three metatarsals along the way. What I found is that behind the novelty of running barefoot or in minimalist shoes, there are real physics. Take the picture above and try to run like that without shoes. You will soon realize that the impact on your heel is painful. You would feel the impact in your foot, your knee, and probably your hip and back, too. With each successive stride, you will almost automatically adjust your form to have a much softer landing, in the middle or fore of your foot. This will cause your stride to shorten, which will quicken your turnover, which will let you breathe better and relax. Soon, you will notice your form looks more like this upon impact:

Good Form

You will still swing your foot out in front of you and fully extend at the knee, but you will contact the ground on the back swing, where your foot is actually just behind your center of gravity. Now, your foot doesn’t have to pull you over it, you are already over it, you just have to fall forward until your other foot swings out in front, then comes back to catch you. This controlled fall is actually a much more efficient running form. Now, since I don’t yet have the skills to animate my stick figures, let’s watch a real human person run.

You can see that the foot swings out and just as it starts to come back, the midfoot makes contact. This allows for a smooth stride that is easy on the knees, hips, and back. Notice I am not barefoot in the video. I am wearing “zero drop” shoes. Zero Drop, or zero difference between the heel stack height and the forefoot stack height, shoes keep the traditional heel pad out of your way so that your foot can swing out and back without interference.

So, do I endorse barefoot running? No, I still think the world is too filthy to go it without some sole coverage. But do I think our shoes should be re-examined? Absolutely! What do we want from our shoes? Protection from rocks, glass, and gross stuff on the ground. What don’t we want from our shoes? How about limitation of motion?

Go back to those different types of shoes (Motion Control, Stability, and Neutral). They all presuppose you are a heel striker. Which type you need depends on how your foot rolls as you progress from heel strike to toe off. If you roll along the inside of your foot, then you overpronate and you have flat arches. The fix? Plug up the arch and put a stiffer material under the inside of your foot. This is called “Motion Control.” In other words, take your weak foot and trap it in a cast. It won’t bother you by trying to get stronger. Let’s say your foot rolls inward, but you have a higher arch. “Stability” shoes may work for you. They aren’t quite as controlling of motion as motion control shoes are at controlling motion. What if you roll outward on the outsides of your foot? You may be “Neutral.” You may not have a problem with your form. Congratulations!

Okay, so the different types of shoes are well intended. How you foot rolls from heel to toe does affect the torsional forces on your knees. But, if you eliminate the heel to toe motion, you eliminate the need to control this upstream torque. In fact, most running related injuries can be mitigated through attention to running form.

So, let’s look at the human foot. Your arch serves a purpose. In conjunction with your calf and knee, your leg is a lever, shock absorber, and wheel all in one. Your calf is a spring and damper while your foot is a leaf spring. They are connected by a pivot at the ankle. Let’s see what we get if I asked my 3-year-old to draw this:

3yr

Okay, let me try….

shock spring

Wow, I thought the comparison might help. Anyway, the foot is a spring, but only if you make contact away from the pivot point (ankle). Otherwise, your spring and damper can’t even help. Heel strikers may as well be double peg-leg pirates. They get no benefit from the lower leg or foot mechanics and rely entirely too much on their hip flexors and hamstrings to do the work.

Hopefully, you get the point. Don’t heel strike. Focus on contact through the backswing of your stride. And, if you are changing up your form, reduce your daily and weekly mileage, prepare for some lower leg soreness, and do not overdo it. If you want my recommendations on shoes – find some with 4mm or less drop, and just enough protection from the terrain you run (rocks, glass, lava, etc).

Good luck. This is one of the most important areas that you should “hack.” Once I paid attention to my form, I stopped getting injured, and I broke through many plateaus in distance and speed. Let me know about your experiences in barefoot, minimalist, heel striking, or pirate running in the comments below.

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