PILARSKI, J.Q*; NISHIKAWA, K.C.; PIEROTTI, D.J.; Northern Arizona University; Northern Arizona University; Northern Arizona University: Motor Unit discharge during ballistic movements in an elite jumper, Osteopilus septentrionalis

Motor unit (MU) discharge patterns during ballistic movements are almost entirely based on human studies in which fine wire or needle electrodes are inserted into superficial muscles under controlled conditions. Studies of other species under more natural conditions have been limited by technical difficulties associated with the placement of microelectrodes that must remain within ≤ 50 �m of an active fiber. The goal of this study was: 1) To evaluate the feasibility of measuring unitary action potentials from single muscle fibers in an amphibian in which the microelectrodes are less prone to interference from the overlying integument. 2) To use an animal model that represents highly derived adaptations for jumping to characterize MU discharge patterns that produce ballistic behaviors. We selected the Cuban tree frog because it can jump 20X its body length when escaping from predators or capturing prey. The plantaris longus was implanted with 17�m tripolar electrodes sutured to the muscle epimysium. 3 cm of the fine wire was threaded under the skin to a solder joint affixed to the back of the animal and to a larger diameter wire connected to a high impedance probe. EMG bursts were initially collected on a tape recorder and then digitized at 20 KHz. The signals were analyzed with a slope/height window discriminator for MU activity. This procedure shows promise in detecting individual units within each burst. EMG activity was also synchronized with 500 Hz digital imaging of the jumps. Preliminary results indicate that single units were captured with minimal movement artifact and a high signal-to-noise ratio. Characterizing MU activity during ballistic movements may enable reexamination of the long standing �size principle� of MU recruitment and neuromuscular control in general.