Mechanical and Energetic Implications of Muscle Function during Locomotion
Overview of approach and techniques:
Understanding the biomechanics and energetics of animal movement is the general goal of the lab. In this context, our work seeks to obtain measurements of the force-length behavior of limb muscles in relation to their activation patterns under in vivo locomotor conditions. This allows a direct evaluation of a muscle's dynamic contractile behavior, rather than relying upon less direct methods of joint moment analysis and kinematics to estimate muscle forces and lengths. Changes in muscle length are obtained by means of sonomicrometry, a technique that uses the propagation of ultrasound pulses between pairs of small piezoelectric crystals implanted along the muscle's fibers to obtain measurements of length. Forces developed by muscles with tendons are determined by the use of tendon force buckle transducers. For certain other muscles, measurements of bone strain obtained from strain gauges bonded to the bone's surface adjacent to a muscle's insertion site provide a second means for calibrating and recording in vivo changes in muscle force. These measurements are combined with fine-wire electromyography to relate the timing of neural activation to force development and length changes. Finally, high-speed video analysis provides kinematic evaluation of limb (or wing) movement patterns produced by the muscles under study.
Use of treadmills enable studies of terrestrial gait to be carried out over a range of locomotor speeds and provide the opportunity to couple studies of locomotor mechanics with oxygen consumption measurements of energy cost. Similarly, use of a wind tunnel for avian flight enables control of flight speed, detailed kinematics of wing motion, and flow visualization past the wing. Finally, the use of a force-platform runway, combined with high-speed video recording, allows ground reaction forces and joint moments to be analyzed in relation to limb mechanics and locomotor energetics.