Changes in windlass effect in response to different shoe and insole designs during walking.

Windlass effect occurs during the pre-swing phase of gait cycle in which the peak tensile strain and force of the plantar aponeurosis (PA) is reached. The increased dorsiflexion angle of the 1st metatarsophalangeal (MTP) joint is the main causing factor. The aim of this study was to investigate thoroughly in finding the appropriate shoe and insole combination that can effectively decrease the windlass effect. Foot kinematic analyses of 10 normal volunteers (aged 25.2±2.1 years, height of 167.4±9.1 cm, and weight of 66.2±18.1 kg) were performed during gait under the conditions of barefoot, standard shoe (SS) with flat insole (FI) or carbon fiber insole (CFI), and rocker sole shoe (RSS) with FI or CFI. The shoe cover consisting of transparent polymer was used for accurate measurement of kinematic data as specific areas on the cover can be cut away for direct placement of reflective markers onto the skin. Under barefoot condition, the mean of maximum dorsiflexion angle of the 1st MTP joint was measured to be 48.0±7.3°, and decreased significantly to 28.2±5.7° when wearing SS with FI, and 24.1±5.7° when wearing SS with CFI. This angle was further decreased to around 13° when wearing RSS with FI or CFI. Subjects wearing footwear alone can increase the minimum medial longitudinal angle and decrease the maximum plantarflexion angle of metatarsus related to the calcaneus as compared with barefoot condition, resulting in flatter medial foot arch. Results suggested that RSS is the effective footwear in reducing the windlass effect regardless the type of insole inserted. The findings in this study provided us with the evidences in finding the appropriate footwear for treating foot disorders such as plantar fasciitis by effectively reducing the windlass effect.