In Vivo Human Gastrocnemius Architecture With Changing Joint Angle at Rest and During Graded Isometric Contraction of Normal and Weak Muscle

Abstract

Architectural properties of the triceps surae muscles complex were determined In Vivo for thirty subjects. These subjects were assigned to two groups. The first group of subjects consisted of 8 healthy men and the second group of subjects was composed of 22 patients with motor disorders. The ankle was positioned at -15 ° (dorsiflexion), and 0 ° (neutral anatomical position), and 15 °, and 30 ° (plantarflexion), with the knee set at 120 °and with an angle in the ankle joint of 90 °. At each position, longitudinal ultrasonic images of the Medial (MG) and Lateral (LG) Gastrocnemius and Soleus (SOL) muscles were obtained while the subject was relaxed (passive) and performed 50 % maximal voluntary isometric plantar flexion (active), from which fascicle Lengths (L) and angles (Θ) with respect to the aponeuroses were determined. From the ultrasonic image, it was observed that and Θ changed during an isometric contraction of the triceps surae muscle. Changes in L and were expressed as a function of relative torque. The Θ change was not identical for the three muscles. The fascicle Θ of MG demonstrated the greatest variation in three muscles. The effects of activation and relaxation positions were significant in all three muscles. The differences in MG fascicle Θ because of changes in ankle positions were significant among control and patients both in the passive and active conditions. Fascicle Θ of LG and SOL not differed among control and patient in the relaxation condition but not in the activation condition. For LG, and SOL ol fascicle Θ were changes were larger in control with the patients. The mean values fascicle Θ of MG, LG, and SOL an isometric contraction (50 % MVC) in the control groups increased by 60 %, 41 %, and 41 %, respectively; in the patient groups were a smaller increase, by 28 %, 26 %, and 36 %, respectively. Different lengths and angles of fascicles, and their changes bу contraction by patients and normal subjects, might bе related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses.