Medial longitudinal arch variations and extrinsic foot muscle elasticity: Analysis of mobile, neutral, and rigid arch...

The mobility of the medial longitudinal arch contributes to foot function by accommodating to varying loads during dynamic weight-bearing activities. Physiologically, an external load, or stress, causes deformation in response to the application of load. Elasticity measures may offer insight into how load is distributed amongst synergistic muscles of the foot. The study's objective was to compare elasticity of extrinsic foot muscles across different categories of medial longitudinal arch mobility.

In this within- and between-subjects exploratory design, shear wave elastography was used to measure elasticity of the tibialis anterior, tibialis posterior, peroneal longus, and peroneal brevis in a non-weight-bearing and weight-bearing condition. Participants (N = 109) were classified into mobile, neutral, and rigid arch categories using the Arch Height Index Measurement System.

In non-weight-bearing, a significant interaction (p = 0.049) revealed elasticity of the tibialis posterior was significantly (p = 0.003, d = 0.90) greater in the rigid arch group when compared to the mobile arch group. In weight-bearing, a significant main effect (p = ≤0.001) for elasticity revealed all muscles, except the tibialis anterior and peroneal brevis comparison, were significantly (p = ≤0.001) different from one another (d = 0.75-3.09).

This study presents a new approach to clinical measures of muscle elasticity using shear wave elastography. The findings offer valuable insight into the mechanical properties of extrinsic foot muscle elasticity across medial longitudinal arch mobility categories and the potential load sharing between synergistic muscles. Results showed elasticity of the tibialis posterior differed between mobile and rigid arches. This information may help inform future research in biomechanics and rehabilitation.