Study aim: There is a lack of evidence to show the presence or absence of a relationship between foot morphology and changes of the force applied to the knee extensor mechanism. The purpose of this study was to examine whether the type of foot is a determining factor in the force applied to the extensor mechanism during walking. Materials and methods: Twenty female subjects (18-30 years), 10 with neutrally aligned feet and 10 with functional flat foot, participated in this study. Data were collected by employing a three dimensional motion capture system and a force platform, while the subjects were walking at their preferred speed. Knee extensor mechanism force was measured at sub-phases of gait (heel strike and toe-off). Results: A significant interaction was found between groups and sub-phases of gait for all the variables tested. The subjects with flat foot exhibited a significantly higher extensor mechanism force at toe-off compared to the control group (p < 0.05). Conclusion: It can be concluded that subtalar hyper-pronation would increase the force applied to the knee extensor mechanism at toe-off, through increasing the knee sagittal angle, net external flexion moment and extensor mechanism moment arm. Therefore it may increase the possibility of musculoskeletal injuries
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