Extending the Paradigm

Irene Davis

Core stability, Evolutionary Biology and the Foot

THE HUMAN FOOT is a complex structure with many articulations and multiple degrees of freedom that play an important role in both static posture and dynamic activities. During standing, it provides our base of support. During gait, the foot must be stable at foot-strike and push-off. However, during mid-support, the foot must become a mobile adaptor and attenuate loads. It also possesses spring-like characteristics, both storing and releasing elastic energy with each foot-strike. This is accomplished through the deformation of the arch, which is controlled by both intrinsic and extrinsic foot muscles. There is evolutionary evidence that the foot arch architecture and musculature developed in response to the increased demands of load carriage and running. The stability of this arch, which we proposed to be the central ‘core’ of the foot, is requisite to normal foot function.

Core stability has received much attention in the clinical and athletic arenas. Interest has primarily been focused on the role of lumbopelvic-hip stability in normal lower extremity movement patterns. The muscular system of the lumbopelvic hip complex, or core, has been described as consisting of local stabilizers such as the multifidus and transverse abdominus, and global movers such as latissimus dorsi. The local stabilizers are known to have small cross-sectional areas and small moment arms. Therefore, they do not produce large rotational moments at the respective joints that they cross. However, they do act to increase intersegmental stability. Proper function of local stabilizers provides a stable base upon which the primary movers of the trunk, those with larger cross-sectional areas and moment arms, can act to cause gross motion. When core muscles are weak or are not recruited appropriately, the proximal foundation becomes unstable and malaligned, and abnormal movement patterns of the trunk and lower extremity ensue. This can lead to a variety of overuse lower extremity injuries.

We propose that the concept of core stability may also be extended to the arch of the foot. The arch is controlled with both local stabilizers and global movers of the foot, similar to the lumbopelvic core. The local stabilizers are the four layers of plantar intrinsic muscles that both originate and insert on the foot. These muscles generally have small moment arms, small cross-sectional areas, and serve primarily to stabilize the arches. The global movers are the muscles that originate in the lower leg, cross the ankle, and insert on the foot. These muscles have larger cross sectional areas, larger moment arms, are prime movers of the foot, and also provide some stability to the arch. With each footstep, the four layers of intrinsic muscles act to control the degree and velocity of arch deformation. When they are not functioning properly, the foundation becomes unstable and malaligned; and abnormal movement of the foot ensues. This may manifest in foot related problems. Plantar fasciitis is one the most common overuse injuries of the foot. It is recognized as a repetitive strain injury from excessive deformation of the arch. The importance of the arch musculature in this prevalent foot injury is currently underappreciated. This is underscored by recent articles describing clinical evidence and guidelines for plantar fasciitis,[9] as well as posterior tibial tendon dysfunction, medial tibial stress syndrome and chronic lower leg pain that have no mention of foot strengthening as a component of the interventions.

Therefore, the purpose of this paper is to propose a foot core system paradigm by 1) describing the evolution of the human arch as it pertains to locomotion, 2) delineating the subsystems of the foot core, 3) reviewing assessment and treatment of the foot integrating the concepts of foot core stability, and finally 4) discussing future research directions in enhancing our understanding of foot function. Our overall goal is to propose a new paradigm in the way we view foot function, assessment, and treatment. We would also like to suggest that perhaps it is time for the Decade of the Foot. This type of attention to a largely ignored, but critical part of our body might help to raise the awareness of the amazing function of our feet and their underappreciated potential for improvement.

ADAPTED FROM: Patrick O McKeon, Jay Hertel, Dennis Bramble, Irene Davis. The foot core system: a new paradigm for understanding intrinsic foot muscle function. BJSM Online First, published on March 21, 2014 as 10.1136/bjsports-2013–092690. Irene Davis, PhD, PT, FAPTA, FACSM, FASB serves as a Professor, Department of Physical Medicine and Rehabilitation Harvard Medical School and the Director of the Spaulding National Running Center.

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