Continuing our Foot Anatomy 101 series, I’d like to discuss the role of natural biofeedback to the proper mechanics of walking and running. Natural biofeedback  is the gathering of information from body receptors in order to monitor and fine-tune body functions. The brain relies on sensory receptors to gather that information.
There are three types of receptors in the human body: exteroceptors, interoceptors and proprioceptors. Exteroceptors gather information from the outside world; interoceptors gather information from internal organs and proprioceptors keep track of body position. When the brain issues a command to move it receives biofeedback from receptors to ensure that the movement is going as planned. When walking, much of that biofeedback comes from exteroceptors in the soles of the feet. Biofeedback has been underappreciated by podiatrists and foot specialists for decades, but scientists (and runners) are beginning to gain a deeper understanding of its role in human ambulation.
With an estimated 100,000 - 200,000 exteroceptors in the sole of each foot, your feet are among the most nerve-rich parts of your body. This fact alone should demonstrate the importance of touch to walking and the benefit of going bare for walking properly. But why are there so many nerve endings in the feet? How do those sensitive soles aid walking?
Stand up and walk around (barefoot). When standing and walking, the sole of your foot is the sole part of your body in touch with the environment . Sensory information from the foot is used to protect the foot itself from injury, but it’s also used by the brain to make subtle adjustments in your gait to protect bones and joints all the way up your body and to maximize the efficiency of your movements. In others words, it makes walking more fluid and graceful and safe. It takes only milliseconds for sensory information from your foot to reach your brain and for your brain to respond by making adjustments to muscles in your legs, back and arms. By contrast, walking in shoes is far more clumsy and inefficient due (in part) to impaired biofeedback. Muscle contractions, impact forces and joint range-of-motion are measurably different when barefoot [3-8].
A typical walking shoe possesses a hard rubber outer sole and a soft cushioned insole. In addition, people generally wear socks with shoes. These materials lift your feet an inch or more from the ground and silence the biofeedback from exteroceptors. In shoes, the brain receives almost no useful information from the soles of the feet. This lack of sensory feedback is called neuropathy and is considered pathological and dangerous under any other circumstance than shoe-wearing. Because foot biofeedback has been unappreciated for so long, shoe-induced neuropathy has also been ignored by doctors for decades.
Walk Barefoot? On Gravel?
Most people have extremely tender feet after years of wearing shoes. This tenderness is partly due to the soft and thin skin which has developed from lack of use, but the perception of pain takes place in the brain not the body. Most of us have been told to wear shoes since early childhood; consequently, our brains are unaccustomed to receiving tactile information from the feet. On those rare occasions when we do walk barefoot, our brains receive ‘sensory overload’ and interpret the strange sensations as painful. Deaf persons who receive their hearing through cochlear implants report their first sounds as painful for the same reason. However, once the brain figures out that the new stimulus is not harmful, the pain subsides. Indeed, what was once considered painful is now re-interpreted as pleasure.
Yes, you can walk and run barefoot on gravel and many other rough surfaces. Gravel poses no threat to your feet, and once your brain discovers this (which can take more than an act of will but time and experience) you can walk on it just fine. And the biofeedback you receive will ensure that your feet and joints are working optimally in addition to providing you with new vistas of pleasure.
Of course, you also need to toughen those tender soles!
1. Artificial biofeedback is an attempt to willfully regulate involuntary body functions being externally monitored.
2. The two other nerve-rich body parts – your hands and mouth – are also parts that frequently contact the environment. The use of touch by your hands is obvious, but your mouth must also use touch to monitor what enters your body. Your mouth is sensitive enough to detect an unwanted stray hair in your bite of cheeseburger.
3. Cunningham et al. (2010). The influence of foot posture on the cost of transport in humans. Journal of Experimental Biology 213:790.
4. De Wit et al. (2000). Biomechanical analysis of the stance phase during barefoot and shod running. Journal of Biomechanics 33:269.
5. Wolf et al. (2008). Foot motion in children shoes – a comparison of barefoot walking with shod walking in conventional and flexible shoes. Gait & Posture 27:51.
6. Stacoff et al. (2000). Tibiocalcaneal kinematics of barefoot versus shod running. Journal of Biomechanics 33:1387.
7. Seth (1977). The foot and footwear. Prosthetics and Orthotics International 1:173.
8. Lieberman et al. (2010). Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature 463:531.