In vivo tibialis anterior muscle mechanics through force estimation using ankle joint moment and shear wave elastography.

Understanding how individual muscles contribute to joint mechanics is crucial for biomechanics. This study investigated the tibialis anterior (TA) shear modulus using shear wave elastography (SWE) and studied its relationship with ankle angle, contraction intensity, and joint moment-derived TA force and stress. Fourteen healthy volunteers (seven females, 26.43 ± 3.67 years) participated. SWE from TA, EMG, and ankle joint moment data were collected across ankle angles (- 15° dorsiflexion to 45° plantar flexion) during rest, maximum voluntary contraction (MVC), and isometric submaximal contractions. TA muscle length, passive ankle joint moment, and TA passive shear modulus increased with increasing plantar flexion (p < 0.001). During MVC, ankle joint moment peaked at 15° (50.13 Nm ± 15.54 Nm) whereas shear modulus remained unchanged (122.96 ± 9.87 kPa) across muscle lengths (p = 0.068). SWE reflected contractions at 25%, 50%, and 75% MVC (p < 0.001). TA force estimates peaked between 15° and 30°, with no significant decrease beyond this range. While SWE captured length-dependent passive properties and contraction intensity changes, the shear modulus at MVC (a stiffness measure obtained from SWE) did not align with the tangent modulus (derived from joint-moment-based force-length characteristics). Emphasizing the need for validation, SWE could serve as a valuable tool for understanding muscle mechanics and muscles' roles in joint dynamics.