The Effects of Terrain Variation on Intrinsic Foot Musculature in Healthy Individuals and Individuals With Plantar Fasciitis

The Human foot is one or the most complicated structures in the conveyance of normal gait, with its 26 bones, 33 articulations, 19 individual intrinsic muscles and direct contribution from all of the lower leg musculature. It also contains a complexity of ligamentous structures that not only act as stabilizers, but also store and release energy in a spring like fashion (Ker 1987). This group of anatomical structures is modulated by a complex system of mechanoreceptors that allow for adaptation to a multitude of varying terrain, while maintaining stability and control. (Franklin 2018) Thus the investigators see the structural, spring and muscular systems all coordinating together to allow for bipedal gait through the natural world.

Multiple observational studies have found an exceptionally low prevalence of common foot pathologies in unshod populations that ambulate on variable terrain daily (Shulman, Choi). At the same time, these same pathologies have become increasingly common in western societies. These findings suggest that something about the western lifestyle is contributing to the development of common foot pathologies. Modern footwear has already been implicated as a contributor to foot pathology and changes in the biomechanics of gait. In a study by K. D'AoÛt et al. on an unshod vs shod Indian population, they found that barefoot walkers had a more equal distribution of peak pressures over the entire load carrying surface than in the habitually shod subjects. The shod subjects had regions of very high or very low peak pressures throughout the load carrying surface.

The increase prevalence of foot pain in the developed world has long been recognized as a significant risk factor for ambulatory disability, (Hill, C. 2008) with plantar fasciitis and hallux valgus being two of the most common causes of foot discomfort presenting in the clinical setting today. Plantar fasciitis accounts for approximately 13% of all foot symptoms requiring professional medical treatment and is believed to be the result of weakening of the intrinsic foot musculature and chronic overload to the plantar foot supportive structure. (Buchanan, B. 2020). Intrinsic foot muscle function seems to play and import role in the development of foot pathology, and is one of the key factors effecting foot health.

The lack of terrain variation found in urbanized western society may directly contribute to the development of foot pathologies. Terrain variation in a minimally shod foot should allow for more coordination and strengthening of the muscular and spring like systems within the foot, through the increase and variation of stimuli encountered by its mechanoreceptors. Lack of terrain variation most probably contributes to a decreased intrinsic foot muscle function and response. There have been many studies showing the correlation between improved intrinsic foot musculature strength and the reduction of foot pain and discomfort, but to date, there are no studies that examined the relationship between terrain variation and intrinsic foot muscle function and strength.

Inclusion criteria

for Group A:

• Patients presenting to the University of Florida Orthopaedics and Sports Medicine Institute with pain on the plantar medial or central heel for greater than 60 days with the following features
• Pain upon palpation, or insidious pain onset
• Pain accentuated after long periods of weight bearing activities or after periods of rest
• A reduction in pain following light activities (McPoil et al., 2008)
• Failure to respond to treatment modalities for 6 months, including plantar fascia and muscle stretching, nonsteroidal anti-inflammatory medication, supportive insoles, and night splints
• Age >18 years

Inclusion criteria

for Group B:

• Healthy individuals in the general population of Gainesville and surrounding areas
• Age >18

Exclusion criteria

for Group A:

• History of lower leg or foot surgery, hindfoot trauma or fracture of the affected limb within the previous year.
• Diagnosis of diabetic neuropathy, fibromyalgia, neurological disease, Achilles tendinopathy, metatarsalgia, tarsal tunnel syndrome or heel pad syndrome
• Body Mass Index (BMI) > 35
• Currently taking or applying any anti-inflammatory medication or medication to control nerve pathology, prescription or over the counter
• Third trimester pregnancy

Exclusion criteria

for Group B:

• Any foot or lower limb pathology resulting in discomfort or gait limitation
• Diagnosis of diabetic neuropathy, fibromyalgia, neurological disease
• BMI >35
• Currently taking or applying any anti-inflammatory medication or medication to control nerve pathology, prescription or over the counter
• Third trimester pregnancy