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How Foot Mechanics Impact Barefoot/Minimalist Training


You may have noticed the explosion in shoe options these days. On one end of the spectrum is the rocker-bottomed "shape up" shoes, while on the other end is the barefoot/minimalist option. What to wear? Should you care? This article discusses foot mechanics and the elements that are important when considering a transition to barefoot training.

"The human foot is a masterpiece of engineering and a work of art."
~Leonardo da Vinci

The human foot consists of 28 bones (including the 2 sesamoids) and 33 joints. It houses 20 muscles that stay in the foot, while 11 muscles cross the ankle from above. (Netter, 2003) The human foot is completely unique from any other animal in the world because we have developed a way to efficiently walk upright.

As the foot hits the ground and the ground hits the foot with an opposite and equal reaction, a lot of energy is absorbed. A good foot will allow all 33 joints to help decelerate this energy, so it can be used to help propel the body forward. Not only that—a good foot will allow the joints above the foot to also help decelerate and absorb impact, and then use this energy for propulsion or un-loading. This is certainly not new information, as the topic of how the foot functions have been discussed before, but let’s refresh our understanding.

When we walk with shoes, the first thing that usually hits the ground is the lateral calcaneus (Michaud, 1997; Wolf, 2006). As the rest of the heel comes down into the ground due to ground reaction forces, the joint below the ankle joint, called the subtalar joint (STJ), will be woken up. At that point, the STJ begins to load. What does “loading” mean? This joint is like a screw in that the bone below (calcaneus) will stay relatively in place, while the bone above (talus) will internally rotate or screw DOWN medially. This is just one way it can help absorb motion, but, remember, this is a joint that operates in three planes. We just described what happens in the transverse plane, but what about the frontal plane? In the frontal plane, the heel will begin go through eversion (hopefully not too much) relative to the talus. What is interesting about the STJ is that, on average, frontal and transverse plane motion is nearly equal. And what about the sagittal plane? Due to the shape of the axis of the STJ joint, not a lot of motion occurs in the sagittal plane. Sagittal plane motion is mostly the responsibility of the ankle joint (talo-crural), which needs to be able to move effectively into dorsiflexion upon loading (Michaud, 1997).

Let’s tie this together. We talked about how a properly functioning subtalur joint (STJ) will cause a combination of subtalur joint motion. Let’s call this pronation, because pronation indicates loading in all three planes. This is when the magic happens. When we walk, our right heel hits the ground. The STJ goes through pronation, which directly affects the Midtarsal Joint (MTJ). This is how humans are different from the rest of the animals in the world. This pronation of the STJ “unlocks” the MTJ, which essentially allows your forefoot (via the MTJ) the freedom and the ability to adapt to almost any ground surface (Gray, 2007; Michaud, 1997).

Let’s summarize: first the STJ pronates, which helps to unlock the MTJ. The MTJ can now adapt to the ground and load through the joints of the forefoot, including the plantar fascia. It’s a great series of events if the foot and the rest of the chain are working as a team. If not, other areas will have to work harder and injuries are more probable.

Improper footwear (which is the kind many people wear) forces the foot into a tiny and often adducted space, with an elevated heel over the forefoot. (Hoffman, 1905; D’Aou et al., 2009) It seems very plausible that many shoes inhibit (to some degree) some of the energy that would normally get dissipated in the foot. The law of conservation of energy states that energy cannot be created or destroyed; therefore, this energy just keeps traveling up the chain. The knee is the joint above the foot that has first dibs on deceleration of this energy. So, you can imagine what would happen if the foot isn’t allowed to do its job properly. Since everything is connected in the body, what the foot doesn't do optimally will only be placed upon other joints up the chain (Gray, 2007; Wolf 2006). Gary Gray and the Gray Institute refer to how the body reacts to the ground as a “chain reaction,” and it truly is. 

Let's go back to when our foot hit the ground. The joints of the foot pronate to absorb energy. If they are successful, rotational energy is delivered to the tibia. This energy doesn’t just stop there. As the old saying goes "the foot bone is connected to the..." The femur sits on top of the shinbone, and all those large gluteal muscles (and other muscles, of course) have a fantastic angle of approach to help decelerate this rotational energy (Gray, 2007; Michaud, 1997). These forces, of course, don’t just stop there. For example, have you ever noticed when you walk that your arms swing opposite your legs? We can also appreciate why our ribcage rotates opposite of the pelvis. Even though we walk forward in a straight line, there is a huge component of rotational energy that is first decelerated, then accelerated. Perhaps this is why most muscles and fascia go at angles and twist and turn throughout the body versus being linear. If your foot is crunched into restrictive shoes with elevated heels, that can make the rest of the body work harder.

The process goes in reverse as well. Trying running or walking fast, but not letting your arms counter-rotate with the legs. In this situation, the top-down deceleration energy is not doing its job, so something below (low back, knee, foot) will have to work much harder to compensate.

Returning to the mechanics of the foot, we briefly discussed how the foot loaded. Now, let’s talk about the foot unloading. This can be very complex, so let’s simplify it. While walking, your right foot is on the ground and behind your pelvis while your left foot and leg are swinging forward. Since that left leg is swinging forward, your pelvis is now rotating to the right. What is the pelvis connected to? Yes, the femur is now beginning to rotate externally. What is the femur connected to? Yes, the tibia then rotates externally. Then what happens? The tibia sits on the ankle, which sits on the subtalur joint (STJ). If you externally rotate the tibia the STJ will now invert (hopefully, if everything is functioning properly) (Gray, 2007; Michaud, 1997).

More magic is about to happen! The heel is beginning to go through inversion, which directly affects the MTJ. Ideally, if the mechanism is working the MTJ will “lock up.” What does that mean? Basically the cuboid bone and the calcaneus will be arranged in a way that provides a tremendous amount of stability. Why is that important? This is simplified, but the foot needs tremendous stability in order to push off (propel), and it’s important in throwing the force of the body towards the 1st metatarsal phalangeal joint (MTP) (Gray, 2007; Michaud, 1997). This mechanism makes us unique in being able to walk efficiently upright. It truly is a work of marvelous engineering.

Unfortunately, there isn’t a lot of research touting the benefits, other then anecdotal. With that, why might it be a good thing for some to train/walk barefoot or minimalist shoes (like Vibrams)? Basically, it allows the foot to do the huge job it was designed to do. (Hoffman, 1905, D’Aou et al., 2009). Second, it makes the weak link in many people stronger, so that it can help the rest of the chain (knee, low back, etc.). Third, I suspect there would be less tripping because you can feel the ground due to more and enhanced sensory information. Fourth, there may be fewer ankle sprains, since many shoes put a huge lever on the heel bone which could possibly promote inversion ankle sprains (Avramakis, 2000; Stacoff et al., 1996; Stacoff et al., 1991). Finally, it truly does feel good to train this way!

Now, a word of caution and a brief discussion of the debate about this trend of going minimalist or barefoot. Many sources indicate that many foot problems are more a result of poor shoe design than the person’s congenital issues (Hoffman, 1905; Rao, 1999; Rossi, 1999). Studies have shown that populations that live mostly barefoot have very few cases of foot problems, including bunions and hallux abducto valgus (big toe that points outward at a large angle) (Hoffman, 1905). More pediatricians are telling parents that children should be barefoot as long as possible because shoes having a negative influence on foot structure and, thus, function. (Staheli, 1991) What can we go from here? For starters, and if your gym or studio allows it, have your clients take off their shoes and move around barefoot. See how they respond. If they move better and have no pain, then you can proceed. If, however, they have immediate pain then going with shoes is probably best for them.

As a trainer, each client is a study of one, so you must always be aware, listen to your client and focus on him or her. What works for 99% of your clients might not work for that remaining 1%, as we are all obviously individuals.

Bottom line: Barefoot training isn't for everyone.

Think about it first.  If the following issues are present, consult a medical professional for advice: bunions, hallux abducto valgus (big toe that points inward at a large angle), large forefoot and/or rearfoot varus, fused ankle joint or other foot joints, diabetes, etc. Be smart and go slowly at first. Very, very slowly. If your client has pain walking barefoot in their home, consider other alternatives.

References

  1. Avramakis, E., Stakoff, A. & Stüssi E. (2000). Effect of shoe shaft and shoe sole height on the upper ankle joint in lateral movements in floorball (uni-hockey). Sportverletz Sportschaden. 14(3): 98-106.
  2. Chain Reaction Explosion Seminar (n.d.). Wynn Marketing: Portland, OR.
  3. Gary Gray and fellows of GIFT Program (2007-2010). Gray Institute.
  4. Hoffman, P. M.D. (1905). Conclusions drawn from a comparative study of the feet of barefooted and shoe-wearing peoples. The Journal Of Bone & Joint Surgery. s2-3:105-136.
  5. D’Aou, K., Pataky, T.C., De Clercq, D. & Aerts, P. (2009). The effects of habitual footwear use: foot shape and function in native barefoot walker. Footwear Science. Vol. 1, No. 2: 81–94.
  6. Michaud, T. (1997). Foot Orthoses and Other Forms of Conservative Foot Care. Newton, MA.
  7. Netter, Frank. (2003). Atlas of Human Anatomy, 3rd Ed. Saunders.
  8. Rao B.U., Benjamin, J. (1992). The influence of footwear on the Prevalence of Flat Foot. The Journal of Bone and Joint Surgery. 525-527.
  9. Rossi, William, DPM (March 1999). Why Shoes Make "Normal" Gait Impossible. Podiatry Management: 50-61.
  10. Rossi, William A. (February 2001). Footwear: The Primary Cause of Foot Disorders. Podiatry Management: 129-138.
  11. Stacoff, A., Steger, J., Stüssi, E. & Reinschmidt, C. (1996). Lateral stability in sideward cutting movements. Med Sci Sports Exerc. 28(3): 350-8.
  12. Stacoff, A., Kälin, X., Stüssi, E. (1991). The effects of shoes on the torsion and rearfoot motion in running. Med Sci Sports Exerc. 23(4): 482-90.
  13. Staheli, L. (1991). Shoes for Children: A Review. Pediatrics. 371-375.
  14. Wolf, C. (2006). Functional Anatomy of the Foot Seminar, Las Vegas, NV.