Meeting Abstract

P3.68  Jan. 6  Hindlimb flexor muscle strain during swimming in the toad, Bufo marinus MILLER, Dery*; GILLIS, Gary; Mount Holyoke College; Mount Holyoke College ggillis@mtholyoke.edu

A number of electromyographic (EMG) analyses of limb function during anuran swimming have shown that major hindlimb extensor muscles are activated nearly simultaneously once per locomotor cycle. In contrast, recent work on hindlimb flexors revealed that activity timing was different among various muscles, and those that can act to flex the knee exhibited two bursts of activity during each swim cycle. To our knowledge, no studies have directly measured length changes in muscles that are bi-phasically active. In particular, we are interested in the potential for eccentric activity in these muscles. Are they lengthening during either of the two EMG bursts, and if so, how much? To address these issues, we implanted pairs of 1 mm sonomicrometry crystals and EMG electrodes into select flexor muscles of interest to record simultaneous muscle activation and strain patterns during swimming in the toad, Bufo marinus. Preliminary results from the iliofibularis show that the muscle�s length changes coincide closely with knee joint excursions. During knee extension in the propulsive phase of the stroke, the muscle stretches, and during knee flexion in the recovery phase, the muscle shortens. Strains range between 9-17% of resting length. A single, short burst of electrical activity is present in the muscle during the last quarter of stretching, and a longer burst of activity is observed during much of the muscle�s shortening. Given the timing of muscle activity with respect to strain, there appears to be only a small degree eccentric activity in the iliofibularis despite the presence of two EMG bursts each cycle. Strain patterns from other major limb flexors, such as the semitendinosus, will be presented for comparison.