On a 6-month sabbatical in beautiful New Zealand (2017) with Professor Grant Schofield, I set out to perform a review of studies aimed at identifying the most common running injuries. Around the same time, I observed kiwi boys running barefoot on a tartan track. We designed a study to better understand the barefoot activity of these boys. In the process of working on these two projects, I came across more and more research articles in this area. I was running myself at the time (sometimes barefoot) and decided to try and write a review piece that would attempt to explain how humans used there physiology and musculoskeletal system to run barefoot. This involved reading lots of different articles from lots of different fields. In the review, I also attempted to discuss how shoes might alter the way these systems behaved. Finally, I made some suggestions as to why incorporating barefoot training on variable surfaces could prove useful to our musculoskeletal health.
A shortened version of this review, known as a letter to the editor, has just been published in the Journal of Sports Medicine and Physical Fitness. The full length review is entitled “From Barefoot Hunter Gathering to Shod Pavement Pounding? Where to from here?”. I am currently revising the full review in the hope of publication.
Here is a brief summary of the letter to the editor entitled: The Urban Runner with an Evolutionary Legacy.
There are 3-major systems which interact to moderate impact when we come in contact with the ground. Bear in mind, they operate in a way that overlaps but for ease of understanding they are described sequentially here.
The first system
Biotensegrity is a term used to describe how all human tissue deforms and subsequently reforms. Your skin, heart, kidneys, muscles etc. all behave in this way. To see this system in action, gently press your finger against the skin on your forearm and watch it deform and reform when you let go. There are elements in all tissues that maintain this stiffness. In the context of the foot, the skin, fat pads and ligaments probably represent this concept most elegantly when the foot makes initial contact with the ground.
The second system
The sensory nerves respond to all sensation and subtle deformations described above. They send this information to the spinal cord for fast (reflex) responses and to the brain for overall control of movement. The brain operates on what it can see (anticipate) ahead and also based on what new information it is receiving from the ground.
The third system
Muscles produce movement and are the major means of absorbing energy on landing. The position of the joint (leg) determines how effectively a muscle can work. For example, to lift an object you bend your elbows, usually to 90°, so that your biceps are at mid-length (the optimum for lifting). If your arms were fully extended you could not generate as much force and if they were fully flexed you could not pick up the object. The exact angle you use comes from what you can see in front of you (e.g. how far or near / high or low the object is in space) and what information you are receiving (initially from your hands and subsequently from your muscles). Running barefoot allows your feet to experience sensation like your hands. The combination of system 1 and 2 can then provide very precise information for your brain to use to optimize joint (leg) positions via muscles.
How might a shoe interfere with these systems?
In relation to system 1 and 2, traditional footwear (work shoes, trainers) is akin to securing a pair of flip flops to the hand. Re-read system 1 and system 2 above and have a think about how footwear may affect the precision of the information to the brain and the subsequent control of movement described in system 3.
Use it or lose it
Our physiology and musculoskeletal systems adapt to stress. For example, if you don’t use a muscle, it becomes smaller. If you don’t use a tendon it looses it’s capacity for energy storage and release. Footwear removes stress from certain parts of our feet e.g. our intrinsic foot muscles. These muscles become weaker. Recent research demonstrates that when you remove the cushioning from shoes, the muscles grow stronger again.
Barefoot or Minimalist Activities in the Prevention or Rehabilitation of Injury
Differences in foot structure between those who grow up barefoot or shod have been described since 1905. Studies that understand the consequences of putting shoes on people who evolved for millions of years to be barefoot are on-going. We do not fully understand how movement skills, injury risk or disease may be influenced by footwear. The clear benefit to footwear is reducing the risk of skin perforation and exposure to extreme temperatures. It becomes less clear what the benefits and risks of footwear are in the context of shoes that alter the shape of the foot or have additional cushioning.
However, based on our discussion so far, let’s put forward a conceptual logic. Proprioception is recommended in the prevention and rehabilitation of musculoskeletal injury in almost every sport. A highly specific form of proprioceptive training for runners would be to remove their shoes and run or walk on a variable surface e.g. at a grass park. The greater freedom afforded to the foot would allow system 1 to deform in relation to the contours of the ground and allow all systems to respond as the ground deforms. In this respect almost no two steps would be the same. As most of us have grown up in shoes, a very careful transition to such activities would be required not to overload our systems – much like any new training intervention.
Thanks for reading. Peter.