Meeting Abstract

5.3  Thursday, Jan. 3  Neuromuscular control of mechanical power output in hummingbirds II: Measurements of muscle work and power. WELCH, KC*; JOSEPHSON, RK; ALTSHULER, DL; Univ. of California, Riverside; Univ. of California, Irvine; Univ. of California, Riverside kenwelch@ucr.edu

Hummingbird flight muscles are predicted to have the highest mass-specific mechanical power requirements of any vertebrate muscle. Although recent advances in aerodynamic theory over the last several decades have led to more refined predictions of the power requirements for hovering flight, empirical measurements of power output have been lacking. Here, we apply a previously developed system for measuring tension while subjecting a target muscle to sinusoidal changes in length to the pectoralis major muscle of Anna�s hummingbirds (Calypte anna). This muscle is exclusively composed of type IIa, or fast oxidative-glycolytic fibers. The uniquely homogenous fiber composition of this muscle permits exceptional clarity in the interpretation of how variation in stimulus and strain patterns affects its force, work and power output. By incorporating variation in strain and muscle stimulation patterns consistent with those recorded from freely hovering hummingbirds subjected to variable gas mixtures or during load lifting, we are able to estimate changes in muscle power output associated with changing aerodynamic performance requirements. Specifically, we demonstrate how patterns of spatial and temporal recruitment of motor units influence the contractile velocity and amplitude of a pure fiber type muscle.