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Footstrike
There has been something of a preoccupation with the footstrike as a marker for clinical risk with barefoot running, presumably since it is relatively easily measured. The fundamental premise is that a forefoot strike, associated with flatter foot placement at touchdown,40 ,41 greater plantarflexion and greater knee flexion angle on impact, distribute the impact force across a greater surface area than the heel alone, thus cushioning the impact. Further, it has been proposed that the plantar fascia is used to create a support system for the arch of the foot and acts as a shock absorber and facilitate elastic restitution during running,41 ,42 and the shift to a more anterior footstrike changes the distribution of eccentric forces across the joints, with an increase in ankle eccentric work and concomitant decrease in loading on the knee joint.43

Complicating the discussion, however, is disagreement in findings relating footstrike to running speed. Hasegawa et al44 and Hayes and Caplan45 found that forefoot striking is more prevalent among faster runners, whereas Larson et al found no difference in footstrike among recreational runners with varying performance abilities. Further, discrepancies may have also been a result of both sample population (recreational vs competitive) and size. The strict characterisation of barefoot runners as forefoot strikers and shod runners as heel strikers is an oversimplification, and possibly incorrect.45 ,46 Indeed, a recent study by Hatala et al showed that heel striking was relatively common among a habitually barefoot population, with 72% landing on their heels at their preferred running speed. Although, as running speed increased, footstrike shifted towards the forefoot, but a significant percentage (40%) remains heel strikers. Thus, the suggestion that barefoot running is synonymous with forefoot striking is thus inaccurate and may obscure the real kinematic differences and their effects on injury risk.47 Interestingly, landing surfaces have been shown to influence the footstrike pattern in runners similarly to the different shoe conditions (and the absence of shoes). Thus, these surface differences may explain discrepancies and unusual findings in different studies and should be noted in future studies involving running.48

Nevertheless, numerous studies have associated footstrike with injury risk. Most recently Daoud et al49 found that runners who habitually rearfoot strike incur a higher injury rate of repetitive stress injuries when compared with runners who mostly forefoot strike. The authors propose that the absence of the impact peak in the ground reaction force during a forefoot strike compared with a rearfoot strike may contribute to lower rates of injury. If this hypothesis is correct, there may be many implications for the running community. However, it must be noted that this study account for performance ability, and the small sample size of 52 runners were divided into 36 rearfoot strikers and 16 forefoot strikers in each group, suggests that further research is required, with larger populations, equally distributed strike types, the type of runner and over a longer period. Alongside this, to categorise footstrike patterns in three clusters may be somewhat reductionist when foot striking has been shown to exist as a spectrum.50

The argument for barefoot running based on this research must however be understood in the light of research from Lieberman et al which found that some habitually shod individuals who run barefoot experience greater impact peaks and rates of loading than habitually barefoot runners.51 This is presumably because they do not adjust their footstrike and continue to land on the heel, exposing them to loading rates sevenfold greater than when in shoes.18 Thus, barefoot running is not by itself sufficient to produce this purported reduction in injury risk, and the transition, which is the logical clinical implication of the advice given to runners, may increase risk, albeit transiently.