Strike is defined as "hitting in a forceful way". The location of strike has been used to distinguish sprinters from distance runners - whether barefoot or wearing shoes of any type, sprinters initially heavily load (strike) their forefoot at first contact, and distance runners initially heavily load (strike) their heel, whether they make first contact with either heel or forefoot. Perhaps starting with Daniel Lieberman, an anthropologist who entered the discussion of biomechanics with no training in mechanics, sports medicine or kinesiology, scientific reports dealing with distance runners, whether barefoot or shod, use first contact as determined by visual records as first strike despite the fact that first contact with forefoot structures is never forceful, therefore actually never a strike. This has created unnecessary confusion and impaired advancement of our understanding of human mobility. If the word "first contact" is substituted for "strike," the discussion of distance running becomes meaningful. When barefoot, the foot makes first contact with the supporting substrate with the foot nearly parallel to the support surface, although first contact may be at the forefoot or heel. This pattern is caused by difference in sensory thresholds along the plantar surface, and pain when the posterior aspect of the calcaneus which is not protected by a fat pad makes contact with the support surface. When wearing typical running shoes, it is more likely that the heel makes first contact with the foot aligned in the sagittal plane so as the forefoot is well above the support surface. The running shoe protects the posterior aspect of the heel from discomfort. This also allows an increase in stride length and greater knee extension when running with running shoes compared to running barefoot, which is cause of most knee disorders in runners. When wearing minimalist (barefoot) shoes with essentially no midsole, a thin outer sole and minimal sockliner, foot position and orientation as well as stride length will resemble more closely the barefoot condition than typical running shoes, because the posterior aspect of the heel tends to become uncombable due to the limited amount of shoe material in these shoes. Remember, that although minimalist shoes can resemble barefoot locomotion in this respect, they are no different than any other shoe in terms of plantar skin tactile sensory feedback, which appears to be the main determinant of injuries related to overloading of foot structures and the amplitude of aggregate impact with human mobility. In a report supported by Vibram, the maker of FiveFingers shoes, Daniel Lieberman suggested that because of this similarity with barefoot running in foot orientation in the sagittal plane at contact, these shoes may offer similar protection. He discounted completely the importance of plantar tactile sensory feedback in protective adaptations. Further, there was no evidence to support this notion. His credibility was called into question when Vibram FiveFingers shoes which by his analysis should have protective value similar to the bare foot in direct contact with the substrate, showed a high incidence of injuries. This information emboldened Vibram to make safety claims about this footwear. This lead to a class action suit for false and misleading advertising by Vibram. It was settled on behalf of the plaintiffs. Daniel Lieberman, et al. Foot strike patterns and collision forces in habitually barefoot and shod runners. Nature:463;531-535:2010. |
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