Meeting Abstract

P3.66  Tuesday, Jan. 6  Fibularis longus function varies with joint angle due to tendon architecture during legged locomotion and jumping in birds. PROPERT, Matthew W.G.*; TRUONG, Rosemary; HITCHCOCK, Amanda C.; MARSH, Richard L.; Northeastern University; Northeastern University; Northeastern University; Northeastern University m.propert@neu.edu

The fibularis longus (FL) is quite unusual in its architecture. As one of the largest of the muscles in the shank of birds, the FL is able to produce a relatively significant force; and its branched distal tendon inserts at three different joints: the ankle, the tarsometatarsal-phalangeal (TMP), and the interphalangeal (IP) joints. Previously some have assumed that the FL functioned at the ankle perhaps because this is the largest branch of the tendon. However, we have shown that the tendon insertions are such that the FL function switches depending on the combination of joint angles. The long tendon that inserts at the TMP passes near the center of rotation of the ankle and this anatomy suggests that the effective moment arm will change depending on the combination of joint angles. We used the tendon excursion method to measure the instantaneous moment arm at the joints when moving one joint and immobilizing the other at various angles. We also measured joint angles in guinea fowl during stationary jumping and legged locomotion as well as determining FL function during these activities using sonomicrometry and electromyography. Our data shows that at the angles used in legged locomotion the FL acts mostly as a toe flexor, but when jumping the FL switches from an ankle extensor early to a toe flexor just before takeoff. We also found that the FL utilizes elastic energy storage to power the jump. Supported by NIH AR47337 and NSF IOB-0542795.