Some abstracts of studies about moving barefoot

Throughout history, members of human societies have gone barefoot, and those societies seemingly had a low incidence of foot deformities and pain. The unshod foot seems to have had minimal problems. Initially shoes were made in the shape of the foot and were sandals. Over time, shoes became decorative items and symbols of status and vanity. As the shape of shoes changed, they became deforming forces on the foot and the source of pain. (Rudicel 1994).

In shoewearing societies a visibly faulty gait can often be corrected and made normal, but it can never be made natural as long as conventional shoes are worn. It is biomechanically impossible because of the forced alterations from the natural in foot stance, postural alignment, body balance, equilibrium, body mechanics and weight distribution caused by shoes. (Rossi 2001).

The skin on the plantar surface of the foot is more resistant to the inflammatory effects of abrasion than skin on other parts of the body. Compared with the hairy skin of the thigh, plantar skin required approximately 600% greater abrading loads to reach pain threshold. We conclude that plantar skin is well protected through sensory feedback from abrasive injuries when barefoot. This information combined with previous reports suggests that risk of injury when normally shod individuals perform barefoot locomotion should be low. (Robbins et al. 1993).

The results of studies examining barefoot activity have consistently shown that the unshod human foot is characterized by excellent mobility, primarily in the region of the forefoot, thickening of the plantar skin up to 1 cm, better alignment of the phalanges with the metatarsals causing the digits to spread, an absence of foot deformities, and mobility of the arches on loading. Observations from countries where barefoot activity is the norm indicates that plantar skin eventually becomes robust and permits extremely long duration of barefoot locomotion at high average velocities, without signs of damage to plantar skin, or for that matter other lower extremity injuries. (Robbins et al. 1993).

Changes in foot biomechanics

An analysis of the biomechanics of the stance phase during barefoot running reveals several differences when compared to shod running. Unlike the dorsiflexed ankle of the shod runner, at heel contact the barefoot runner’s ankle is plantar flexed leading to a more horizontal position for the foot. A more horizontal foot would have fewer shear forces acting on the heel. Also, maximum pressure on the heel is reduced with a more horizontal foot at touchdown. The lower leg is more vertical for the barefoot runner at this point thanks to a greater knee flexion. Both the increased plantar flexion of the ankle and increased knee flexion occur prior to touchdown suggesting an “actively induced adaptation strategy to barefoot running.” (De Wit et al. 2000).

During this initial contact phase, sensory feedback from the glabrous epithelium of the bare foot brings about greater flexibility of the foot. This suppleness helps the foot adapt to irregular ground surfaces and allows it to act as a shock absorber. Much of the shock absorption during this phase occurs through natural pronation and the associated downward deflection of the medial longitudinal arch. Much of this is tempered, or even lost, in the shod foot. Sensory feedback is greatly diminished by the insulating sole of the shoe. The result is a more rigid foot which disables the deflection of the medial longitudinal arch reducing the foot’s ability to moderate impact shock. Arch supports built into most shoes further reduce the ability of the arch to deflect. (Robbins & Hanna 1987).

Midstance is the time of the greatest ground reaction force. One study found the impact peak in barefoot running to be 14% lower than in shoe conditions. This reduction may occur because the impact peak and the end of midstance happen significantly sooner for the barefoot runner. The percentage difference in the amount of time it takes to the end of midstance is directly proportional to the velocity of the runner; a study found barefoot runners moving at 3.5 m/s reached the end of midstance on average 17% sooner than the shod runner, the difference became 22% at 4.5 m/s, and it grew to 24% at 5.5 m/s.3 An additional benefit of the barefoot runner reaching the end of midstance sooner is the related rapid rate of pronation that has been associated with a decreased chance of developing overuse injuries. (Kersting et al. 1999, Hrlejac et al. 2000).

Footwear modifies some of the characteristics of the propulsion phase in other ways. Several of these changes are related to the aforementioned elevated heel of the shoe. One byproduct of heel elevation is a shortening of the Achilles tendon and calf muscles. As these muscles become shorter, they fail to pull properly on the back of the heel thereby increasing the flattening of the arch. Pronation occurs at a time when the foot should be in a neutral position. The unnatural position of the elevated heel also disrupts the work of some tendons connected to the toes. These tendons, which originate in the lower leg, apply their pull around ankle bones above the heel to hold the toes against the ground while the body passes over them during propulsion. The raised heel leads to an imbalance in the tug of these tendons thereby interfering with efficient propulsion. (McClanahan 2003).

Perhaps the greatest hindering effect of elevated heel is the loss of the involuntary stretch reflex of the Achilles and posterior lower leg muscles. This stretch reflex is designed to aid the forefoot with propulsion, yet it can only be activated if the heel comes close to the ground. The elevated heels of most available footwear, including athletic shoes, prevent this stretch reflex from occurring. The result is a loss of propulsive power. The runner’s body is forced to borrow power from other areas – knee, thigh, hips, trunk – to compensate for the sidelined Achilles tendon and calf muscles. According to podiatrist William A. Rossi, “ANY shoe with an elevated heel, even a one-inch heel, automatically places the foot at a functional disadvantage.” (Rossi 2001).

Sensory feedback

Another reason for potentially fewer knee problems for barefoot runners can be traced to adaptations at the ankle and knee joints. Studies have shown that runners adapt to a running surface by modifying their lower leg stiffness. For the barefoot runner, the changes in lower extremity geometry include a decrease in knee joint stiffness and a corresponding increase in ankle joint stiffness compared to the shod runner. This results in the ankle becoming the site of greater impact absorption. For the shod runner, the impact absorption demand on the knee is greater. Considering that up to 30% of all running injuries are related to anterior knee pain, the adoption of barefoot running must be considered as a method for reducing knee injuries in runners. (Kurz & Stergiou 1999, Hardin et al. 2000, Ounpuu et al. 2000, Coyles et al. 2001).

Barefoot runners can also expect fewer sprains of the ankle. Ankle sprains are the most common acute injury suffered by athletes. It is claimed that footwear increases the risk of such sprains, either by decreasing awareness of foot position provided by feedback from plantar cutaneous mechanoreceptors in direct contact with the ground, or by increasing the leverage arm and consequently the twisting torque around the subtalar joint during a stumble. Runners who frequent trails or uneven surfaces may be especially vulnerable to this type of injury. Since nearly all (90-95 %) ankle sprains are inversion injuries, it behooves athletes to find ways to improve their lateral stability. The best lateral stability, with mostly reduced inversion, is found in the barefoot condition. Also, imperfect proprioception can cause the foot to be placed in an awkward position. Compared to being barefoot, foot position awareness has been shown to be 107.5% worse when wearing athletic footwear. Siff and Verkhoshansky (1999) reported that running shoes always reduce proprioceptive and tactile sensitivity. The authors of this study believe, “The inescapable conclusion is that footwear use is ultimately responsible for ankle injury.” (Robbins et al. 1995, Stacoff et al. 1996, Warburton M 2001).

The modern running shoe and footwear generally reduce sensory feedback, apparently without diminishing injury inducing impact a process described as the “perceptual illusion” of athletic footwear. A resulting false sense of security may contribute to the risk of injury reasoned that once the natural foot structures are weakened by longterm footwear use, people have to rely on the external support of the footwear, but the support does not match that provided by a well functioning foot. (Robbins & Gouw 1991, Yessis 2000).

Summary made by:

Petri Väyrynen
Oy Feelmax Ltd
[email protected]