The Barefoot Journal: A LITTLE SCIENCE
I would be remiss not to include some of the information available from experts in the field. I have been doing some excellent reading, so the next installment will be a more technical view of barefoot activity.
My guidebook for the last few days has been “The Barefoot Running Book Second Edition: A Practical Guide to the Art and Science of Barefoot and Minimalist Shoe Running” by Jason Robillard. It is proving to be a great beginner’s tour, and I am about to embark upon his training program. Although I am not here to endorse products, this book is a must-have for anyone interested in transitioning from shod running (wearing traditional running shoes). Jason’s website provides additional information, as well as a free sample of the book.
It’s a good idea to have an understanding of the mechanics of propulsion through the foot. This article , from jointpaininfo.com, will give you a “running” start:
BASIC FOOT ANATOMY
The foot is made up of 26 bones, which are divided into three sections called the rearfoot, midfoot and forefoot. The talus and calcaneus (heel bone) are the bones that make up the rearfoot. The talus is the highest bone in the foot and it is also part of the ankle. The calcaneus is the largest bone in the foot. It sits below the talus. The navicular, cuboid and the three cuneiforms are the bones that make up the midfoot. The five metatarsals and nine phalanges are the bones that make up the forefoot.
There are three arches in the foot. There is an inner (medial) arch, an outer (lateral) arch and an arch in the forefoot called the transverse arch. Ligaments are like strong ropes that connect bones and provide stability to joints. In the foot there are numerous ligaments that support the arches and stabilize the bones. These ligaments are located on the top (dorsal), bottom (plantar) medial and lateral aspects of the foot.
The plantar fascia is a key structure that helps support the medial and lateral arches of the foot. The plantar fascia is a strong connective tissue that runs along the bottom of the foot connecting the heel to the base of the toes. When weight is put on the foot the plantar fascia helps to “lock” the bones of the foot and stabilizes these arches.
Many of the muscles that move the foot originate from the lower leg. These muscles attach via tendons to various bones in the foot. The muscles that move the foot upwards (dorsiflex the foot) originate on the front of the lower leg. The muscles that move the foot outwards (evert the foot) originate on the lateral aspect of the lower leg. The muscles that move the foot inwards (invert the foot) originate deep on the back of the lower leg. The muscles that move the foot downwards (plantarflex the foot) and propel the body forward originate from the knee and the back of the lower leg. The muscles that play the largest role in propulsion are the calf muscles (gastrocnemius and soleus muscles). These muscles join to form the Achilles tendon that attaches onto the calcaneus. In addition to the long muscles, there are also numerous short muscles in the foot. These muscles also play a role in stabilizing the arches of the foot and in moving the toes.
Finally, there are numerous fat pads located on the bottom of the foot. These fat pads act as “cushions” or “shock absorbers”. The largest fat pad in the foot is located in the heel directly below the calcaneus. There are other “cushions” or “shock absorbers” in the foot called bursae. A bursa (pl. bursae) is a small fluid filled sac that also decreases the friction between two tissues and protects bony structures. There are many different bursae around the foot.
This excerpt from Jason Robillard’s book, found on the free .pdf sample available at his website, takes things a bit further. It is an excellent description of the neuromuscular activity involved in running. Let me warn you, however; it may take a couple of reads to really understand the process. Well worth the effort, however.
Recently Dr. Scott Hadley, founder of TrekoClinics.com, summed up the reasons for and history behind barefoot/
minimalist running in his article titled, “This is Your Body on Shock: stretch reflexes, shock absorption, and barefoot/minimalist running.” That article, used with his permission, follows:
In 1898, a neurophysiologist named William Sherrington published his findings on stretch reflexes. The basic idea of a stretch reflex is this: when a muscle is lengthened rapidly, a signal is sent to the central nervous system which triggers that muscle to contract. The “knee jerk” reflex is one example thatyou have probably seen when your doctor hits your knee with a little rubber hammer. The rapid stretch of the quads triggers a reflex that causes the muscle to contract—and the knee jerks.
In 1956, another neurophysiologist name J.C. Eccles reported that the stretch of one muscle not only causes reflex activation of that muscle, but other muscles are activated too. Eccles thus defined two types of stretch reflexes. A homonymous stretch reflex occurs when the stretch of a muscle causes that muscle to contract. A heteronymous stretch reflex occurs when the stretch of a muscle causes a different muscle to contract. During the past 60 years, heteronymous stretch reflexes have been investigated extensively by neurophysiologists. Through surface EMG recordings in human subjects, dozens of heteronymous reflex patterns have been identified. It is thoughtthat these reflexes allow the central nervous system to monitor and control gait and other complex human movements at an automatic, subconscious level.
Essentially, our body movements are in large part controlled by a series of stretch reflexes between muscles. When walking and running, the nervous system reads ‘stretch information’ from several key muscles and uses that information to activate or inactivate other muscles in a coordinated sequence. This is how we can walk, run, and perform other complex movements without thinking about it.
Let me give you a few examples of the role of stretch reflexes during running. When the foot hits the ground (initial contact), the first muscle to contract is the soleus of the calf—if you are landing properly without a heel strike. Forward momentum causes the soleus to stretch rapidly, and the soleus reflexively contracts to prevent the knee from buckling. While the soleus contracts, it also lengthens to allow the knee to advance over the foot (this is called an eccentric muscle contraction for you physiology buffs). Stretch reflexes from the lengthening soleus act as a powerful neurological switch that activates the quadriceps and hip extensors to prevent the leg and trunk from collapsing under the forces of landing on one foot. In fact, if the soleus doesn’t stretch properly, the hip extensors can be up to 75% weaker due to a lack of heteronymous reflexive control.
The muscles in the bottom of the foot (the foot intrinsics) also play a role as body weight is accepted onto the foot. The foot intrinsics begin undergoing a lengthening (eccentric) contraction as the arch of the foot flattens slightly to absorb shock. The stretch reflexes initiated from the lengthening of the foot intrinsics produce an interesting mechanism of shock absorption at the knee and ankle by inhibiting the soleus and quadriceps—causing partial relaxation of these muscles—to allow the ankle and knee to give-way slightly as body weight is loaded onto the leg.
If the foot arch is over-supported by an orthotic or a motioncontrol shoe, the foot intrinsics are incapable of inhibiting the soleus and quadriceps. At a phase in the gait cycle where the soleus and quadriceps should be slightly more elastic to absorb shock, they remain more rigid, thus reducing shock absorption and causing excessive strain on the soleus, quadriceps, and joint structures. Over time, if the arch is over-supported, the foot intrinsics become weak and are no longer effective. The foot intrinsics become weak and tight, stretch reflexes become inhibited, muscles do not ‘turn on’ when they need to, and biomechanics break down. The end result is overuse injury— something most runners experience at some point.
But barefoot and minimalist running allows the foot arch to deform naturally, allowing the stretch reflexes from the
foot intrinsics to activate a very effective shock absorption mechanism. It’s almost counterintuitive that running barefoot or in minimalist shoes produces less impact than running in supportive, padded running shoes. But research has shown just that. And the stretch reflexes from muscles in the foot are partially responsible for this.
Since the foot intrinsics are used more in barefoot and minimalist running, we invariably go through a phase of
muscle soreness and growth of the foot intrinsics and soleus during the transition out of standard running shoes and after a long run. But rejoice in your aching foot muscles! This is your body absorbing shock as nature intended.
Scott Hadley, Ph.D, DPT
I will add more articles, images and videos as we go along. See you next time!