Use of Three-Dimensional Ultrasonography for the Analysis of the Fascicle Length of Human Gastrocnemius Muscle During Contractions

Abstract

The fascicle lengths of the human gastrocnemius muscle during isometric plantar flexions were analyzed using a three-dimensional ultrasound system (3D-US). Prior to measurements in vivo, the accuracy and reproducibility of the 3D-US were examined by taking images of a phantom. The horizontal errors were 0.3-1.0%, and the vertical errors were 1.2-1.6%. In addition, the coefficients of variance for the repeated measurements were 3.3% and 1.7% for horizontal and vertical directions, respectively. Second, both at rest and each of five intensities {20, 40, 60, 80, 100% of maximum voluntary contraction (MVC)}, at a fixed ankle joint angle of 90deg, the 3D-US images of gastrocnemius muscles were obtained and used to determine fascicle length. The fascicle length was also measured using two-dimensional ultrasound system (2D-US), and the values obtained by 2D-US were used to make comparisons with those by 3D-US. From rest to MVC, the fascicle length decreased as a function of relative torque levels from 6.0 (± 0.5) cm to 3.1 (± 0.4) cm with 3D-US, and, in a similar manner, from 5.6 (± 0.5) cm to 3.0 (± 0.4) cm with 2D-US. Thus the present study indicated the accuracy and reproducibility of the 3D-US measurements and its usefulness for determining the fascicle lengths of human muscles in three-dimensional space. The fascicle length measurements determined by 3D-US were, however, significantly longer than those of 2D-US.