Meeting Abstract
The typical locomotor mode of bats is flight, but many species swim capably. Earlier studies have characterized the kinematics of swimming in the big brown bat (Eptesicus fuscus) as a low-amplitude version of their flight kinematics. The kinematic differences could arise from fundamentally different motor patterns during the two locomotor modes, or from similar motor patterns realized differently in air versus water, fluid media with different physical properties. To explore these alternatives, we asked whether activation and recruitment patterns of several limb muscles in bats differ between flight and swimming We measured fore and hindlimb joint kinematics and electromyography (EMG) from biceps brachii (short head), triceps brachii (lateral head) and gracilis in E. fuscus. Our experiment allowed each subject to fly and swim with the same EMG implants. We then examined relationships between onset and peak timing of EMG and joint kinematics (shoulder, elbow, hip and knee flexion-extension) using cross-correlation analyses to determine phase-lag. After accounting for difference in medium by duty-cycle normalization, lags between peak muscle intensity and peak joint kinematics were significantly larger during swimming than flight. During flight, all three muscles were active during joint movements supported by their anatomical lines of action. By contrast, during swimming, their activation timing shifted by up to 75-80% of the limb motion cycle, to coincide with the opposite joint movement. This finding suggests that energy might be stored elastically in the slender tendons of triceps, biceps and gracilis during swimming. Studies of muscle and tendon length change during swimming and flight will help test this hypothesis directly. Funded by AFOSR.
