Flatfoot is a risk factor for patellofemoral pain syndrome (PFPS), and excessive rearfoot eversion occurring in flatfoot has been associated with the development and progression of PFPS; however, the mechanism remains unclear. This study aimed to investigate transverse shank and frontal rearfoot coordination patterns and variability when running with normal foot and flatfoot. Participants with normal foot (n = 13) and flatfoot (n = 13) were asked to run at their preferred speed. The coupling angle between the shank and rearfoot, representing intersegmental coordination, was calculated using the modified vector coding technique and categorized into four coordination patterns. Standard deviation of the coupling angle was computed as a measure of coordination variability during the stance phase. No differences in the characteristics and spatiotemporal parameters between groups were found, and all participants had rearfoot strike pattern. During midstance, the flatfoot group showed a significantly greater proportion of anti-phase with proximal (shank) dominancy than the normal foot group (p = 0.04, effect size = 0.88 [large]). Furthermore, flatfoot group showed a significantly greater in variability than the normal foot group (p = 0.03, effect size = 0.91 [large]). This study’s results may help explain why flatfoot is likely to result in PFPS. However, the occurrence mechanism of running injuries like PFPS is multi- factorial. Since these results alone are not sufficient to explain the cause-effect relationship between flatfoot and injuries like PFPS, a prospective study including other factors such as patellofemoral joint stress would also be needed.

扁平足是pa股疼痛综合征（PFPS）的危险因素，扁平足中发生的过量后足外翻与PFPS的发生和发展有关。但是，机制尚不清楚。这项研究旨在调查正常脚和扁平足跑步时横小腿和额叶后足的协调模式和变异性。正常脚（n = 13）和扁平足（n = 13）的参与者被要求以他们喜欢的速度跑步。使用改进的矢量编码技术计算代表节间协调的小腿与后脚之间的耦合角，并将其分为四个协调模式。计算站立角度期间耦合角的标准偏差作为协调变异性的量度。两组之间的特征和时空参数均无差异，所有参与者均具有后足打击模式。在中间状态期间，扁平足组的反相占近端（小腿）优势的比例明显大于正常足组（p = 0.04，效应量= 0.88 [大]）。此外，扁平足组的变异性比正常足组大得多（p = 0.03，效应量= 0.91 [大]）。这项研究的结果可能有助于解释为什么扁平足会导致PFPS。但是，像PFPS这样的行驶伤害的发生机理是多因素的。由于仅这些结果不足以解释扁平足与PFPS等伤害之间的因果关系，