Fueling and performance in a high speed locomotor muscle

点击翻译按钮获取中文摘要

This research examines some of the ways that the fueling and mechanical performance of locomotor muscle varies in relation to body size and muscle operating frequency. The distinct hovering flight of hummingbirds is the most energetically and mechanically costly form of locomotion employed by any vertebrates. The pectoralis and supracoracoideus muscles, responsible for powering the downstroke and upstroke, respectively, of the hummingbird wingbeat, operate at a range of frequencies inversely related to body mass with small hummingbirds employing the fastest locomotor muscle operating frequencies of any vertebrate. Past research has revealed some of the anatomical and biochemical features that enable the hummingbird pectoralis to achieve high rates of aerobic metabolism. However, many questions regarding aspects of the source of fuels oxidized during hovering, mechanisms for modulation of muscle performance, and quantification of contractile properties of high speed locomotor muscle, including how these features vary in relation to body mass or muscle operating frequency, remain unanswered. The research in this proposal will address three main questions: 1) How do capacities for the use of newly ingested, versus endogenous fuels during exercise vary among hummingbirds of varying body size and hovering metabolic rate? 2) How do patterns of neuromuscular control of the pectoralis vary in relation to wingbeat frequency? 3) Is there a tradeoff between maximal force and operating frequency (contraction speed) in hummingbird pectoralis muscles? To answer these questions we will couple studies of hummingbird fuel use, kinematics, and neuromuscular control (EMG) patterns on freely hovering hummingbirds with studies of the contractile properties of isolated hummingbird pectoralis, including species across a range of body mass with varying wingbeat frequencies for study. The results will increase our understanding of the limits to muscle performance and fueling at high frequencies and identify tradeoffs among various aspects of muscle physiology that apply generally to all locomotor muscles.