Relationship between joint torque and muscle fascicle shortening at various joint angles and intensities in the plantar flexors.
Because it is difficult to measure tendon length changes directly in humans, tendon length changes during dynamic movement have been evaluated indirectly from changes in muscle fascicle length and joint angle. The purpose of this study was to examine the validity of the indirect method. Twitch contractions of the ankle plantar flexors were evoked isometrically in eight subjects. Twitch contractions evoked by singlet, doublet, and triplet stimulations were conducted at dorsiflexion 20° (DF20), plantar flexion 0° (PF0), and plantar flexion 20° (PF20). Muscle fascicle length and pennation angle were recorded by ultrasonography. The magnitude of muscle fascicle shortening was significantly smaller in DF20 than in PF0 and PF20, although the magnitude of joint torque was significantly larger in DF20 than in PF0 and PF20. Theoretically, the magnitude of tendon elongation is expected to be larger in larger joint torque conditions. However, we found that the magnitude of tendon elongation evaluated from muscle fascicle shortening was larger in a lower joint torque condition (PF20). These results suggest that the magnitude of muscle fascicle shortening does not necessarily represent tendon elongation. The larger muscle fascicle shortening in PF20 may be partly caused by eliminating slack of the muscle-tendon complex.
The Research Organization of Science and Technology, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga, 525-8577, Japan. atsukifukutani@gmail.com.|Japan Society for the Promotion of Science, Research Fellowship for Young Scientists, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo, 102-0083, Japan. atsukifukutani@gmail.com.
Atsuki
A
Fukutani
Graduate School of Sport and Health Science, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga, 525-8577, Japan.
Jun
J
Misaki
Faculty of Sport and Health Science, Ritsumeikan University, 1-1-1 Noji-higashi, Kusatsu, Shiga, 525-8577, Japan.
Tadao
T
Isaka
D000328:Adult; D033023:Foot Joints / Q000033:anatomy & histology* / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D016059:Range of Motion, Articular; D013710:Tendons / Q000033:anatomy & histology* / Q000502:physiology*; D019415:Torque; D055815:Young Adult