To understand the biomechanics of human walking is to understand your bellybutton. If the entire mass of your body were concentrated into a marble, it would live at the exact level of your bellybutton. The evolution of human propulsion has developed to move this small marble, or your center of gravity, as efficiently as possible.
As a child, we crawl to keep this center of gravity as low as possible until we have developed the strength to raise its level so we can then free up our upper limbs to grasp and work. In addition to strength, complex coordination develops to minimize the rise, fall, and sway of this center of gravity so we can move through space with as little consumption of calories and oxygen as possible. This coordination requires a dance with every possible muscle in the human body. To observe a person will with even the slightest paralysis of face or arms will reveal a subtle limp as they walk. For those who may have had an extra bourbon or two will also realize the complexity of this coordination.
Running sacrifices the efficiency of walking for the sake of speed. Running is defined by a moment in time when both feet are off the ground and the body is airborne. Instead of the gentle sinusoidal roll of our center of gravity, running creates a jarring spiked curve much like the breaking waves near shore.
Modern running shoes have been designed to help minimize the impact associated with heel strike by raising the height of the shoe with cushion. In addition, reinforcement on the inner and outer border of the shoe helps stabilize the joints of the foot so the more major muscles of the legs (quadriceps and hip flexors) will take a larger share of the load. These shoes have allowed for a longer stride and greater impact on the leg than would normally be tolerated by the body. Many orthopedic surgeons believe that running injuries are associated with forces, which exceed the tolerance of the bones, tendons, and ligaments of the body. Poor training technique or poor balance of the muscles of the body may contribute to these injuries.
Barefoot running or running with minimalist shoes creates greater contact between the foot and ground. The heel is on the ground. There is little or no support of the inner or outer border of the foot. As the body moves into a running motion, there is a shorter stride and less extension of the knee or hip when the foot strikes the ground. Heel strike occurs at the center of gravity as opposed to in front of this point. As a result, the forces of impact at heel strike are absorbed by most of the muscles of the legs in a balanced fashion. In particular, the calf muscles and hamstrings absorb much more force than in traditional running. Less force goes across the joints of the leg and more goes towards the muscles. There is greater eccentric contraction of muscles since there is less lock out of our joints. Physiologically, al this is called PreActivation. The center of gravity moves in a smoother sinusoidal curve mimicking walking and there is less side to side sway of the torso as well.
As a result, barefoot running can create a smoother, shorter stride running gait that imparts less stress across joints. It forces the center of gravity more forward in the body, which transfers more forces onto muscles rather than static joints and ligaments.
Clearly barefoot running is not for everyone. However, running is not for everyone. But for those with a strong interest in the biomechanics of running, barefoot running will provide a better understanding of role of our bodies in injury and injury prevention. In particular, it’s about how the interface between the body and the ground relates to the coordination of all the muscles and joints above it.
Here are few additional references if you are interested:
Thomas H. Lee, M.D.