The foot-core system - part 4 of 7

McKeon, Hertel, Bramble, and Davis (2013), researchers in the Department of Kinesiology, Ithaca, New York, developed a novel concept in understanding the structure and important role of the foot relative to postural uprightness, balance, and movement. In their study, they presented an outline of the many functions of foot musculature, and proposed that the structure of the foot could be correlated to the structure and function of the abdominal core. They referred to this new paradigm as the foot core system. One of the goals of their content was to create a new perspective in viewing the kinematics of the foot and its’ role in movement and balance for the entire skeletal structure. They opened their discussion detailing the complexity of foot musculature, and the diversity of functions it facilitates in standing, gait, and dynamic movement. Special focus was called to the archit

ecture of the foot dome which they pose as the "core" of the foot, also called the “arch” of the foot. Relevance of core stability was correlated to normal foot function. Researchers further elaborated on the foot core system by breaking it down into 3 subsystems of neural, passive, and active, and the role each subsystem plays in the foot core system.

The active subsystem includes 2 groups of muscles called extrinsic and intrinsic. The extrinsic muscles are known as global movers and generally originate from the lower leg. They are responsible for large movements of the foot such as plantar and dorsiflexion, eversion and inversion. They also contribute towards providing dynamic support for the ankle and foot dome control. The intrinsic muscles originate and insert within the foot. They are known as local stabilizers and are comprised of 4 layers of muscles superior to the plantar aponeurosis. These smaller muscles control corrective foot movements which assist in stabilization and balance. They also include sensory receptors which respond to posture imbalances by minute stretch responses. Sensory adjustments in these muscles inform the lumbo-pelvic muscles to react in a similar manner efforting to retain balance and uprightness.

The passive subsystem comprised of bony articulations maintains all of the weight of the skeletal structure above while standing or moving, and influences foot dome flexibility during loading and unloading of the arch. The arch of the foot is structured like a vault and considered the base of the foot. This vault-like structure supports postural alignment and is framed by a triangular base formed from the big toe, to the little toe, and to the heel. The arch plays an important role in shock absorption and facilitates movement propulsion. The role of intrinsic muscles in supporting the arch of the foot is important in normal foot function.

In gait, the foot arch is depressed into deformation and then released allowing the natural ‘spring tension’ of the arch to reconstruct itself. Plantar fasciitis is a repetitive deformation of the arch which has lost its ability to spring back to the natural shape. Whether standing or moving, the disbursement of weight falls emanating from the top of the talus, and following cascade patterns of lateral, medial, and superior arches, into the ground. Passive subsystem includes the half dome structure bones of the arches, plantar fascia, and ligaments, unified together below the ankle joint. This joint has a mortise and tenon structure facilitating plantar and dorsiflexion. Below it is the subtalar joint which allows for lateral glide in the frontal plane permitting eversion and inversion. All components are continually micro adjusting at the region of the talus to maintain balance and uprightness of the human structure as a whole.

The neural subsystem is made up of sensory receptors which both send and receive messages efforting to alter spinal motion and forces to stabilize the upper skeleton. Afferent signals received from the plantar area of the foot and fascial sensory receptors throughout intrinsic foot muscles and plantar aponeurosis, are sent to the central nervous system (CNS). CNS responds by sending efferent messages to appropriate muscles throughout the body to alter spinal movement, and adjust to forces. Intrinsic foot muscles, also receive messages to adjust at the talus and subtalar regions. All subsystems work in unison as the foot core system with a biotensegrity-like response.

Scientific data suggests that human foot structure already possessed an unusually well-defined medial longitudinal arch structure, compared to primates who had similar arboreal and terrestrial foot structure, and further evolved as the result of habitual locomotor activities in terrestrial bipedality (McKeon, Hertel, Bramble, & Davis, 2013). A more spring-like tension also developed in both Plantar and Achilles tendons as a response to humans bearing weight while moving (this pertains to carrying heavy objects or basic gait in which the spring tension system is loaded and unloaded with every step). The foot core system originates from this premise and considers the development and strengthening of intrinsic foot muscles with the short foot exercise in particular, as tantamount to maintaining normal structure and health of arches. Researchers conclude that foot core training is extremely important and begins with an ability to differentiate between the foot core in the relaxed and contracted state, and continues with training the plantar intrinsic muscles. The foot core system, comprised of the active, passive and neural subsystems, work simultaneously and cohesively to maintain uprightness and balance while the body is static or dynamic.