Changes in aponeurotic dimensions upon muscle shortening: in vivo observations in man

Aponeurotic deformation measurements have traditionally been taken by loadi ng dissected muscles; thus the values obtained may not reflect in vivo func tion. In the present study, we estimated dimensional changes in the central aponeurosis of the intact human tibialis anterior muscle upon loading indu ced by muscle contraction. Measurements were taken in seven males, and invo lved real-time ultrasound scanning of the tibialis anterior muscle at 30 de grees of plantarflexion at rest and during isometric dorsiflexion maximum v oluntary contraction (MVC). At each contraction state, the length of the ap oneurosis, the width along its length, and its area were estimated from sag ittal-plane and axial-plane sonographs. In the transition from rest to MVC, the length of the aponeurosis increased by 7% (P < 0.05), its width increa sed by up to 21% (P < 0.05), and its area increased by 17% (P < 0.05). Thes e results indicate that the in vivo tibialis anterior aponeurosis behaves a s a compliant material upon active muscle shortening. The methodology emplo yed allows cross-sectional and longitudinal design investigations, circumve nting the problems associated with epimysial removal under in vitro experim ental conditions.