
Using a combination of vertical loading rates and electromyographic data, Williams, et al., attempted to explain the differences in leg stiffness during gait between runners with high and low arches. They identified a direct relationship between lower extremity stiffness and performance, as well as injury. These methods included measuring ground reaction forces, vertical trajectory of center of mass (using a force plate), and foot contact time, among other parameters. They looked at several methods for calculating the vertical and linear stiffness of the lower extremity during gait. In a review of various published models of leg stiffness, Butler, et al., found substantial biomechanical evidence to support the concepts above. 8 A high-arched or inflexible foot can increase this normal stress in ranges that result in symptoms and pathologies.Ī growing body of evidence helps to explain why high-arched individuals (especially athletes) are reporting greater incidence of bone and joint stress injuries. Steven Subotnick estimates that running multiplies the impact of heel strike on the body by approximately three times (the "Rule of Three"). 7 This is the equivalent of a 160-pound man being hit in the head by 80 pounds with each step.ĭr. Within 10 milliseconds of heel strike, scientists studying normal walking recorded a. In normal subjects, the force of heel strike transmits a shock wave (a "transient") up the leg to the pelvis, the spine and into the skull. The stress of impact while walking is also minimized when the foot pronates normally and the leg flexes to absorb shock. When there are equal magnitudes of pronation and supination during standing and walking, rotational equilibrium results and no significant rotational velocity is imparted to the adjacent structures. A higher-than-normal arch can be a particular problem when there is significant asymmetry, especially if the other foot has little or no arch. 5 This type of foot generally requires improved flexibility ( mobilization, stretching) and stabilizing orthotics to help decrease shock at heel strike. Having a rigid, high-arched foot makes one susceptible to development of stress fractures in the sesamoids, calcaneus, femur and pelvis.


This results in poor attenuation of heel-strike shock, much of which is then transmitted up the kinetic chain into the leg and hip. The foot with a higher-than-normal arch remains too rigid and inflexible during walking and running. Problems arise when there is too little or too much mobility in the foot and ankle. Normal amounts of movement are necessary for biomechanical function during activities of stance and gait. 4 While less frequently found, foot stiffness and hypomobility (a lack of pronation, usually with a high arch and fixed supination) can also be the underlying causes of significant lower extremity biomechanical distress. 3Ī 2004 paper dealt with the common problem of excessive foot flexibility and hyperpronation during gait. In fact, a study by Dahle, et al., found that athletes with either excessively pronated or supinated foot types were significantly more susceptible to knee injuries than those who had a normal pronation mechanism to absorb shock.

"A high-arched (cavus) foot with limited range of motion attenuates shock poorly and a hypermobile flat foot also does poorly on shock attenuation because of its function near the end of the range of motion." 2 This helps explain how both types of foot dysfunction can contribute to musculoskeletal symptoms and injuries. Whenever there is either too little pronation (as is found in fixed supination), or excessive pronation, the effects of impact loading are amplified. The study concluded that this was because an elevated arch tends to transmit, rather than absorb, heel-strike shock, as does the foot with a normal arch. In fact, an investigative study by Simkin, et al., conducted during a military basic-training session, found a much higher frequency of femoral stress fractures in recruits who had a cavus (high-arched) foot. However, too much arch can be just as much of a problem as not enough.

Many articles have discussed how excessive pronation and the loss of the foot's medial arch ( flat foot) can negatively affect the mechanics of the lower extremities, as well as the pelvis and spine.
