The foot core system: a new paradigm for understanding intrinsic foot muscle function
Article Review by Evan Peterson PT, DPT
Over the years, there has been much discussion regarding building “core” muscle and stability. When the term “core” is used, generally the public immediately is drawn to the abdominal and trunk musculature. In this article by McKeon et al (2014), the writers discuss the importance of a different core system. They address the need for further attention to the intrinsic portion of the foot alongside the extrinsic muscle system for improved mechanics and function.
Throughout our normal gait pattern, the human foot has to go through many adjustments and adaptations to allow for the most efficient gait possible. Each phase of the gait cycle requires the different structures to stiffen or become mobile for proper energy storage and release. If the 4 intrinsic layers of the foot do not operate appropriately it may lead to unwanted deformation of the arch, which in turn, leads to a variety of problems such as plantar fasciitis, posterior tibial tendon dysfunction, medial tibial stress syndrome, and chronic lower leg pain.
The authors discuss the origin of the human foot and its development of arches defined by long and strong ligaments, an adducted great toe, shortened lateral toes, and compaction of the mid tarsal region to help prevent collapse. Apes unlike humans also lack the pronounced Achilles tendon and plantar aponeurosis designed for storing and releasing energy required for running. Humans, unlike quadruped runners, also have the additional intrinsic foot muscle system. Quadruped runners rely almost solely on passive stability from ligaments.
Due to the above-mentioned facts, McKeon et al, suggest the idea of the “foot core system” which working together provides stability and flexibility to accommodate varying surfaces and loads. The system consists of 3 different subsystems: Passive, Active, and Neural. The passive system consists of the bones of the foot which create a half dome, the plantar fascia, and ligaments of the foot. The active subsystem of the foot consists of both intrinsic and extrinsic foot musculature. The extrinsic muscles start in the lower leg and cross the ankle joint; whereas, the intrinsic are all located below the ankle joint. The intrinsics and extrinsics along with the passive system work synergistically to allow for proper foot function. The neural system accounts for the proprioceptive aspects of the plantar fascia, ligaments, joint capsules, muscles and tendons. It is proposed that the foot intrinsics play a key role in detecting quick stretches allowing for correction in foot dome posture.
Despite the evident importance of the core muscle system, currently there is no gold standard for measurement of the foot intrinsics. Most testing looks at flexion strength which does not completely isolate the intrinsic system and also does not test the person’s ability to maintain an arch. The authors suggest an intrinsic foot muscle test, which looks at the ability to maintain and the medial longitudinal arch while in single limb stance after the therapist sets the foot in subtalar neutral. The goal is to maintain the arch without excessive global muscle involvement.
To address any deficits found, it is suggested to utilize the “short foot” exercise as opposed to toe flexion exercises like the towel crunch in order to eliminate flexor hallicus longus and digitorum longus involvement. McKeon et al relate this to the idea of the abdominal draw in maneuver used for lumbopelvic core stability. It is necessary to build a strong base to allow for the other moving parts to perform correctly. Several studies, as mentioned in this article, have shown the short foot exercise to improve balance and self-reported function in those with chronic ankle instability.
Due to the importance of our foot’s core, the authors believe barefoot/minimal footwear is ideal for training the intrinsic foot musculature. Studies have shown increase in foot core muscle size while wearing barefoot shoes as well as have demonstrated improvements in balance and postural stability. The authors do not suggest this method for those with altered sensation in their feet.
The authors believe, at first adding external support to the foot in an acute injury is acceptable; however, the support should be removed as soon as possible to allow for strengthening of the foot core.
Here at Physical Therapy First, you can work with a physical therapist 1 on 1 for an examination and be instructed in the proper way to address your foot’s core.
Reference:
McKeon, P. O., Hertel, J., Bramble, D., & Davis, I. (2014). The foot core system: A new paradigm for understanding intrinsic foot muscle function. British Journal of Sports Medicine, 49(5), 290–290. https://doi.org/10.1136/bjsports-2013-092690