Mechanical properties of tendon and aponeurosis of human gastrocnemius muscle in vivo

Load-strain characteristics of tendinous tissues (Achilles tendon and apone urosis) were determined in vivo for human medial gastrocnemius (MG) muscle. Seven male subjects exerted isometric plantar flexion torque while the elo ngation of tendinous tissues of MG was determined from the tendinous moveme nts by using ultrasonography. The maximal strain of the Achilles tendon and aponeurosis, estimated separately from the elongation data, was 5.1 +/- 1. 1 and 5.9 +/- 1.6%, respectively. There was no significant difference in st rain between the Achilles tendon and aponeurosis. In addition, no significa nt difference in strain was observed between the proximal and distal region s of the aponeurosis. The results indicate that tendinous tissues of the MG are homogenously stretched along their lengths by muscle contraction, whic h has functional implications for the operation of the human MG muscle-tend on unit in vivo.