Today you’ll pick up the very basics of feedback and feed-forward mechanisms that relate to the merits and limitations of minimal shoe choices in training situations. As movement in general and gait in this particular sense are to an extent controlled by sensory information collected, processed, and translated into motor potentials via the nervous system, it stands to reason that alterations of this sensory data can lead to different outcomes or variances of movement pattern selection
Afferent neurons are present throughout the body, and there are few places that have them in greater densities than the feet. The cervical spine, lips, and hands are about the only areas in which afferent cells are present in greater density. For the visual learners amongst us, below is a picture of the neuro-homunculus, which has traditionally been used to scale the presence of afferent neurons throughout the body.
Now, the body is a pretty impressive piece of machinery and there are few things within it that are not purposefully placed. As you can see, there is clearly a LOT of afferent neurons in the feet, and if my last statement is at all true, they are there for areason. Why are they there?
Afferent neurons are present in the feet and surrounding joints and structures to detect magnitudes and rates of loading, joint kinematics, and pressure distribution on the plantar surface of the foot. This sensory information is then integrated into motor commands at all levels of the central nervous system. The central nervous system utilizes the incoming sensory information in two distinct ways. The first is that this sensory data helps the brain to formulate internal commands to drive the output of neural messages during voluntary movement. The second is the use of sensory information to let the CNS know of errors in the execution of movement that allow for correction or alteration of movement patterns. These pathways are collectively referred to as feed-forward and feedback mechanisms of gait control and is used to modulate motor patterns and motor activity.
As the foot is the only interface with the ground during running, there should be little question that these afferent neurons play a role in controlling running gait. In fact, this is the case, and afferent feedback helps to modulate muscle activation patterns, total energy required to run, leg stiffness, and joint kinematics throughout gait.
To help you understand why this matters, say you are our for a run this spring and and you step on a patch of remaining ice, and your foot slips out from under you. As soon as your foot contacted the ice, the afferent sensors present in the skin, muscles, tendons, and joints sent a series of signals demanding compensatory movements to prevent you from landing on the back of your head. Without adequate afferent stimulation, the odds of the effective compensatory reactions go down significantly, and your likelihood of hitting the trail increase markedly. This, however, is an extreme example, and the afferent neurons via feedback and feed-forward loops are at work during each and every stride or each and every run.
In the coming days we will discuss feedback and feed-forward mechanisms a bit more and then discuss how changes in footwear style and qualities may play a role in altering these systems and subsequently altering gait. We’ll then discuss strategies of how to optimize your training environment to get the most out of these mechanisms.