The Relationship between Features of Foot Posture, Thickness of Intrinsic Foot Muscles and Dynamic Postural Stability

PURPOSE: This study aimed to determine the correlations between foot posture features, intrinsic foot muscles (IFMs) thickness, and dynamic postural stability.METHODS: Forty-one male participants were divided into two groups according to quantified foot postures using the Foot Posture Index (FPI-6) scores: the neutral foot group (FPI-6 score: 0 to +5) and the pronated foot group (FPI-6 score: >+6). The IFMs thickness was measured using ultrasound images of the flexor digitorum brevis (FDB), flexor hallucis brevis (FHB), and abductor hallucis muscles. To investigate the association between IFMs thickness and dynamic postural stability, the Biodex Balance System (BBS) was used in a single-leg stance position with both the eyes open and closed.RESULTS: In the BBS tests, the pronated foot group demonstrated significant results in the eyes-closed condition (p<.05). In particular, the differences between the eyes open and closed conditions in postural stability indices were significantly greater in the pronated foot group than in the neutral foot group (p<.05). No significant differences in IFMs thickness between the two groups were observed; however, some subdomains of the FPI-6 demonstrated significant positive correlations with postural stability indices and significant negative correlations with IFMs thickness (p<.05). The talonavicular joint was associated with FDB thickness (R=-0.311). Moreover, the forefoot was correlated with FHB thickness (R=-0.327).CONCLUSIONS: The aforementioned results suggest that dynamic postural stability and IFMs thickness are affected by the foot type. Although no significant differences in IFMs thickness were observed, dynamic postural stability and IFMs thickness reduced as the foot displayed features of pronation. This indicates that postural control ability and IFMs are vulnerable to changes in foot posture.