Cupiennius salei: biomechanical properties of the tibia-metatarsus joint and its flexing muscles

• Published in: Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology Vol. 180; no. 2; pp. 199 - 209
• Main Authors: Siebert, Tobias, Weihmann, Tom, Rode, Christian, Blickhan, Reinhard
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01-02-2010; Springer-Verlag; Springer Nature B.V
• Subjects: Animal Physiology; Animals; Biochemistry; Biomechanical Phenomena; Biomedical and Life Sciences; Biomedicine; Female; Human Physiology; Joints - physiology; Life Sciences; Locomotion - physiology; Models, Biological; Muscles; Muscles - physiology; Original Paper; Spiders - physiology; Zoology; Force–velocity; Spider; Arthropod; Muscle properties; Force–length; Contraction dynamics
• ISSN: 0174-1578; 1432-136X
• DOI: 10.1007/s00360-009-0401-1

Hunting spiders are well adapted to fast locomotion. Space saving hydraulic leg extension enables leg segments, which consist almost soley of flexor muscles. As a result, the muscle cross sectional area is high despite slender legs. Considering these morphological features in context with the spider's segmented C-shaped legs, these specifics might influence the spider's muscle properties. Moreover, these properties have to be known for modeling of spider locomotion. Cupiennius salei (n = 5) were fixed in a metal frame allowing exclusive flexion of the tibia-metatarsus joint of the second leg (counted from anterior). Its flexing muscles were stimulated supramaximally using needle electrodes. Accounting for the joint geometry, the force-length and the force-velocity relationships were determined. The spider muscles produce 0.07 N cm maximum isometric moment (corresponding to 25 N/cm² maximum stress) at 160° tibia-metatarsus joint angle. When overextended to the dorsal limit at approximately 200°, the maximum isometric moments decrease to 72%, and, when flexed to the ventral hinge stop at 85°, they drop to 11%. The force-velocity relation shows the typical hyperbolic shape. The mean maximum shortening velocity is 5.7 optimum muscle lengths per second and the mean curvature (a/F iso) of the Hill-function is 0.34. The spider muscle's properties which were determined are similar to those of other species acting as motors during locomotion (working range, curvature of Hill hyperbola, peak power at the preferred speeds), but they are relatively slow. In conjunction with the low mechanical advantage (muscle lever/load arm), the arrangement of three considerably actuated joints in series may nonetheless enable high locomotion velocities.