Meeting Abstract
43.2 Tuesday, Jan. 5 Decoupling of muscle shortening and joint kinematics during frog jumping ASTLEY, H. C.*; ROBERTS, T. J.; Brown University; Brown University henry_astley@brown.edu
Elastic tendons can decouple changes in muscle length from changes in joint angle, allowing the muscle to function at closer to optimal conditions for force production and allowing elastic energy storage in the tendon. While elastic tendons have been well-studied in steady-speed locomotion, their role in acceleration is not well understood. The remarkable jumping ability of anurans is an excellent system for addressing this issue due to well-characterized muscle physiology, extensive prior work, static pre-jump posture, and recent data suggesting that elastic energy storage in tendons may occur. In order to test the hypothesis that elastic tendons decouple muscle contraction from joint movement during accelerations, we quantified simultaneous joint movement and muscle contraction in the ankle of Rana pipiens. The ankle is extended almost exclusively by the plantaris, a large pennate muscle with a long, prominent tendon sufficient to generate noticeable decoupling. Jumps were studied using X-ray Reconstruction Of Moving Morphology (XROMM), a high-speed biplanar X-ray cinefluoroscopy system, with radiopaque markers implanted into the muscle and bones to simultaneously track muscle strain and joint movement. Preliminary data from 7 jumps shows 7.7% (±0.8%) shortening strain of the muscle fascicle preceding any substantial joint movement, followed by a 38.7° (±3.4°) joint extension with minimal muscle fascicle length change, after which both joint and muscle display rapid change. Fascicle strain rate showed peaks prior to the initiation of joint movement and shortly after maximal joint angular velocity, separated by a period in which the strait rate was close to zero with high angular acceleration of the joint. These data indicate a decoupling of muscle strain from joint angle as well as the storage of strain energy in the tendon. Funded by NSF Grant 064242.
