Predictability of in vivo changes in pennation angle of human tibialis anterior muscle from rest to maximum isometric dorsiflexion

The aim of this study was to assess the predictability of in vivo, ultrasou nd-based changes in human tibialis anterior (TA) pennation angle from rest to maximum isometric dorsiflexion (MVC) using a planimetric model assuming constant thickness between aponeuroses and straight muscle fibres. Sagittal sonographs of TA were taken in six males at ankle angles of -15 degrees(do rsiflexion direction), 0 degrees (neutral position), + 15 degrees (plantarf lexion direction) and + 30 degrees both at rest and during dorsiflexor MVC trials performed on an isokinetic dynamometer. At all four ankle angles sca ns were taken from the TA proximal. central and distal regions. TA architec ture did not differ (P > 0.05) neither between its two unipennate parts nor along the scanned regions over its length at a given ankle angle and state of contraction. Comparing MVC with rest at any given ankle angle! pennatio n angle was larger (62-71%, P < 0.01). fibre length smaller (37-40%, P < 0. 01) and muscle thickness unchanged (P > 0.05). The model used estimated acc urately (P > 0.05) changes in TA pennation angle occurring in the transitio n from rest to MVC and therefore its use is encouraged for estimating the i sometric TA ankle moment and force generating capacity using musculoskeleta l modelling.