24.6 Wednesday, Jan. 4 The Effect of Passive Joint Elements on the Movement Output of the Frog Ankle SALZMAN, RE*; SCHWARTZ, JM; AHN, AN; Claremont McKenna College; Harvey Mudd College; Harvey Mudd College email@example.com
In order to understand the role of passive elastic elements in movement, we examine the position output of an intact ankle joint in the American bullfrog (Rana catesbeiana). Upon stimulation, the plantaris longus muscle (PL) extends the ankle, which then passively recoils completely to return the ankle to its initial ankle position in less than a second. Similarly upon stimulation, the tibialis anterior muscle (TA) flexes the ankle, which then passively, fully recoils back to its original position. The antagonistic muscle might passively cause this recoil like a rubber band pulling the limb back into place. For this reason, we hypothesized that cutting the antagonistic muscle and tendon would eliminate or reduce the recoil in the ankle joint. The unstimulated, antagonist muscle-tendon unit contributed in determining the rest position of the joint for both the PL and the TA. The rest angle of the ankle joint with the PL intact and the TA cut (N = 7) increased by 15 ± 9° (extension). With the TA intact and the PL cut (N = 7), the rest angle of the leg decreased by 51 ± 11° (flexion). However, after the muscle was stimulated, the antagonist muscle-tendon unit had no effect on the speed or magnitude of recoil of the ankle joint. Beyond the muscle-tendon unit, joint elements such as the ligaments or capsule may play a larger role in the movement of the frog ankle joints than previously expected. These findings could have implications for the design of biomechanical lever systems, such as the use of passive elements in prosthetics and robotics. We thank HHMI, Barbara Stokes Dewey, REBMI (NSF-0634592), a Baker Award, and the HMC Biology Department for funding.