Superficial and deep aponeuroses movements in the human medial gastrocnemius during isometric plantarflexion contraction

Abstract

In pinnate muscle such as medial gastrocnemius (MG), the aponeuroses are located on both sides of the muscle. It has been reported that superficial (SA) and deep aponeuroses (DA) of the MG are stretched homogenously along its length by isometric contraction. However, it is impossible to elongate the entire aponeuroses, because the proximal edge of each aponeurosis attaches to the femur. We hypothesized that at certain locations each aponeurosis is shortened by isometric contraction. Velocity encoded‐phase contrast MRI was used to measure velocity and displacement of each aponeurosis in 4 subjects during repeated plantarflexion (20 and 40% loads). The velocities of each aponeurosis increased and was positive during the contraction phase, declined to zero at peak torque, and then became negative during the relaxation phase, suggesting both moved proximally during contraction and moved distally during relaxation. The displacement moved the least in middle region of the SA and proximal region of the DA along its length. These results indicate that the SA lengthened in the proximal region and shortened in the distal region, and the DA shortened in the proximal region. However, the displacement of the distal region may have been overestimated since the length of this region was of the same order as the fascicle length.This work was supported by National Institute on Arthritis and Musculoskeletal and Skin Diseases Grant.