Meeting Abstract

71.1  Wednesday, Jan. 6  Primary Downstroke Muscle Activity and Shoulder Movements in Free-tailed Bats. HERMANSON, J.W.*; ALTENBACH, J.S.; Cornell Univ., Ithaca; Univ. of New Mexico, Albuquerque jwh6@cornell.edu

We explored several hypotheses about primary downstroke muscle function and skeletal motion in free-tailed bats (Tadarida brasiliensis). Bats were implanted with 0.2 mm diameter stainless steel pins in the proximal humerus and acromial process of the scapula to visualize skeletal motions. EMG analysis followed protocols described in our previous studies (J. Zool., 205:157) and used a 16 mm high speed cine recording system. All bats were recovered and released afterwards. Kinematic analysis revealed the dorsal scapulo-humeral interlock was maintained during the first half of the downstroke and that clavicular adduction is nearly synchronous with wing adduction. The caudal division of the serratus ventralis muscle was not anatomically suited to contribute to adduction of the humerus as has been hypothesized in previous studies. Although free-tailed bats are rapid, long-distance fliers, several of their downstroke muscles exhibited a biphasic recruitment pattern similar to that found in some other bats that fly in cluttered environments, including Artibeus jamaicensis which fly under and within the forest canopy. The onset and termination of primary EMG activity in serratus ventralis precedes the onset and termination, respectively, of the pectoralis muscle. By opposing the caudal component of force exerted by the pectoralis muscle, the caudal division of serratus ventralis facilitated ventrolateral displacement of the clavo-scapular articulation and effected clavicular adduction. These actions may reduce the excursion of the pectoralis and may contribute to its efficiency during flight.