Barefoot running has become an increasingly popular in the past several years as more and more examples find themselves falling into the popular media. So what is the deal? Is there any credence to the craze?
Yesterday we gained an elementary knowledge of the foot and ankle’s anatomy. Today, you’ll take home a comparison of mechanics in barefoot subjects and those who wear shoes.
Before we begin, it would be prudent to define a few things. The term “shod” refers to some level of modern footwear that is typically characterized by a softer midsole, elevated heel, and potentially some form of “motion” control type devices. Runners whether barefoot or shod can contact the ground with either the rearfoot (RFS), midfoot (MFS), or forefoot (FFS) and these patterns appear to be significantly related with choice in footwear.
Barefoot Running vs. Shod Running
Gross differences in mechanics are evident between the two varieties of running that are first worth noting. In comparison, barefoot running results in shorter strides and greater frequencies with shorter stance phases than shod athetes. Additionally, the barefoot runner typically (and variations do occur between subjects) contacts the ground in a relatively plantar flexed, flat foot position with a more relative vertical shank, and makes contact with greater surface area along the foot than shod runners. Trunk angle is closer to vertical an the barefoot athlete with a contact position closer to bottom dead center and in the gluteus maximus’s “wheel house” moreso than shod running. Most often, skilled barefoot runners make use of FFS patterns, while shod runners make use of RFS patterns, which has a profound impact in elastic response (Lieberman, 2010) (discussed in tomorrow’s post).
Impact force peaks between the two conditions are generally identical, however, some have published two impact peaks in shod conditions while only a single impact peak is seen in barefoot (Eslami, 2007). Additionally, there are only small differences between joint loads between the two conditions, with barefoot running seeing greater external loading (Dickinson, 1985). It has been shown that shod runners experience no differences in vertical force peaks and maximum vertical loading rate regardless of sole thickness and stiffness, and some suggest a greater peak impact force in shod running conditions (Nigg, 1986). The directions of the forces are also different in barefoot and shod. In barefoot conditions, horizontal forces are lower, reducing shearing forces at the calcaneus, which may be important in reducing the risk of calcaneal stress injury, which the second most common tarsal stress fracture. Shod runners have also shown greater knee flexion torques, varus torques, and hip internal rotation torque compared to barefoot athletes (Kerrigan, 2009).
It was once thought that barefoot runners execute compensatory motions to attempt to reduce forces to the level of shod athletes, yet this has been challenged lately. Pronation (the combination of abduction, dorsiflexion, and eversion) is used as a shock attenuation mechansim, however, less eversion is evident in barefooted athletes throughout stance, which may have implications with those experiencing IT band dysfunction (Pohl, 2006; Ferber, 2010). Some mechanical changes are evident, though, indivdual specific with changes in knee flexion angle in response to stiffer surfaces being a commonly cited response. Additionally, barefoot runners have greater forces at the hallux (Wiegerinck, 2009), contributing to potentially better Windlass mechanism function. Additionally, similar loads between conditions may be a result of altered pre-activation patterns evident between shod and barefoot runners (Nigg, 2001).