Meeting Abstract
98.8 Wednesday, Jan. 7 Flexor vs. extensor activity during jumping and swimming in Rana pipiens NOYES, N*; GILLIS, GB; Mount Holyoke College; Mount Holyoke College ggillis@mtholyoke.edu
Despite widespread study of jumping and swimming in anurans, little is known about the functional roles of limb flexor muscles in these animals. Work in toads demonstrates some overlap in extensor and flexor activity bursts during propulsion. To further explore flexor function in relation to extensors, we characterized activity patterns in antagonistic muscle pairs acting at the knee and ankle during jumping and swimming in Rana pipiens. Specifically, we implanted electrodes in the cruralis (CR) and semitendinosus (ST) to characterize EMG activity at the knee, and in the plantaris (PL) and tibialis anterior (TA) to characterize activity at the ankle. Our results indicate that all four muscles exhibit some coactivation during jumping and swimming. During jumping, all muscles exhibit nearly simultaneous EMG bursts lasting throughout much of takeoff. Intensities of bursts correlate positively between muscles, but negatively with the duration of the takeoff phase. During swimming, extensor activity is characterized by a single burst at the onset of limb extension. Flexor activity is more complex. The ST exhibits two EMG bursts per cycle. Burst 1 is closely aligned with activity in the extensors, and its intensity is positively correlated with extensor activity. Burst 2 is present later during limb retraction (~60-90% of swim cycle), and exhibits relatively little variation in intensity. The TA exhibits one long activity burst that begins late in limb retraction (~90% through the swim cycle) and lasts into limb extension, where its timing overlaps with extensor bursts. TA intensities correlate positively with intensities in both the PL and CR. In summary, major flexors and extensors are coactive during the propulsive phase of jumping and swimming, but flexor activity patterns shift considerably between the two locomotor modes.
