ESSNER, R.L.*; NAUWELAERTS, S.; ROME, L.C.; University of Pennsylvania; University of Pennsylvania; University of Pennsylvania: Forelimb and caudopelvic function during takeoff in Rana pipiens

The forelimbs of frogs are thought to play balancing or positioning roles during takeoff. However, they may also be important in raising the center of mass (CoM) via forelimb extension prior to takeoff. Conversely, frogs may elevate their CoM solely with their unique caudopelvic (CP) muscles in order to control takeoff angle by: 1) modulating amplitude of the CP muscles; or 2) changing the timing of the motor pattern relative to hindlimb extensors. In order to test these hypotheses we studied Rana pipiens (n=15) jumping over short (<20 cm) and long (>45 cm) distances, with an integrated setup consisting of high-speed video (250 fps), EMG, and force plates. Frogs were placed so that they bridged two separate force plates as a way of distinguishing relative contributions of fore and hindlimbs to ground reaction force. In order to examine muscle activity, bipolar electrodes were placed in the following muscles: m. semimembranosus (hindlimb extensor); m. coccygeoiliacus (trunk elevator); m. anconeus (forelimb extensor); and m. coracoradialis (forelimb flexor). Long jumps in R. pipiens are characterized by significantly higher mean amplitudes for each of the four muscles examined. However, muscle activation patterns appear to be similar in both types of jumps, with all four muscles being activated simultaneously, suggesting that phase regulation of CP muscles is not the primary mechanism by which frogs control trajectory during normal jumping. In addition, forelimb force records lacked a consistent peak in the vertical direction suggesting that forelimbs do not play a major role in raising the CoM during most jumps.