The aim of the present study was to determine the transverse strain of aponeuroses in human tibialis anterior muscle (TA) in vivo and to clarify the influence of muscle fiber length and state of contraction on the transverse strain. Sagittal and horizontal images of TA were taken in seven men and one woman at ankle angles of –20° (dorsiflexed direction), 0° (neutral anatomic position), and 45° (plantar-flexed direction) both at rest and during submaximal dorsiflexion contraction (20 Nm: 0° and 45°; 10 Nm: –20°) using B-mode ultrasonography. The width of the TA central aponeurosis changed from 21.7 ± 1.0 (mean ± SE) to 25.5 ± 1.1 mm when muscle fiber length changed from 91.0 ± 3.5 (45° in the resting state) to 55.1 ± 3.2 mm (–20° in the active state). The transverse strain of the TA central aponeurosis, which was change in relative width compared with the width at 45° in the resting state, increased when the muscle fiber length decreased. The transverse strain of the TA central aponeurosis was directly proportional to the muscle fiber length to the –1/2 power in both resting and active states (R = 0.81 and 0.74, p < 0.05 for both), and there was no significant difference (p < 0.05) between correlation coefficients and regression slopes for resting and active states. The findings suggest that the transverse strain of the TA central aponeurosis was closely related to muscle fiber length and that the transverse strain of the aponeurosis should be considered for accurate 3-D muscle modeling.
T. Muraoka and H. Kanehisa are with the Dept. of Life Sciences, Graduate School of Arts and Sciences, University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo, 153-0041 Japan; T. Muramatsu is with the Japan Institute of Sports Sciences, Kita, Tokyo; T. Fukunaga is with the Dept. of Sports Sciences, Waseda University, Tokorozawa, Saitama, Japan.