ARCHITECTURAL AND FUNCTIONAL FEATURES OF HUMAN TRICEPS SURAE MUSCLES DURING CONTRACTION

Architectural properties of the triceps surae muscles were determined in vivo for six men. The ankle was positioned at 15 degrees dorsiflexi on (-15 degrees) and 0, 15, and 30 degrees plantar flexion, with the k nee set at 0, 45, and 90 degrees. At each position, longitudinal ultra sonic images of the medial (MG) and lateral (LG) gastrocnemius and sol eus (Sol) muscles were obtained while the subject was relaxed (passive ) and performed maximal isometric plantar flexion (active), from which fascicle lengths and angles with respect to the aponeuroses were dete rmined. In the passive condition, fascicle lengths changed from 59, 65 , and 43 mm (knee, 0 degrees; ankle, -15 degrees) to 32, 41, and 30 mm (knee, 90 degrees ankle, 30 degrees) for MG, LG, and Sol, respectivel y. Fascicle shortening by contraction was more pronounced at longer fa scicle lengths. MG had greatest fascicle angles, ranging from 22 to 67 degrees, and was in a very disadvantageous condition when the knee wa s flexed at 90 degrees, irrespective of ankle positions. Different len gths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscl es and elastic characteristics of tendons and aponeuroses.