Fueling and performance in a high speed locomotor muscle

这项研究探讨了运动肌肉的燃料和机械性能随身体大小和肌肉工作频率而变化的一些方式。蜂鸟独特的盘旋飞行是任何脊椎动物采用的能量和机械成本最高的运动形式。胸大肌和上喙肌分别负责蜂鸟翼拍的下击和上击，它们在与体重成反比的频率范围内工作，小蜂鸟采用任何脊椎动物中最快的运动肌肉工作频率。过去的研究已经揭示了一些解剖学和生物化学特征，使蜂鸟胸肌能够实现高速率的有氧代谢。然而，许多问题，关于燃料的来源，在悬停过程中氧化，肌肉性能的调制机制，以及高速运动肌肉的收缩特性的量化，包括这些功能如何变化的身体质量或肌肉工作频率方面，仍然没有答案。本提案中的研究将解决三个主要问题：1）在不同体型和盘旋代谢率的蜂鸟之间，运动期间使用新摄入的与内源性燃料的能力如何变化？2)胸肌的神经肌肉控制模式如何与翅拍频率有关？3)蜂鸟胸肌的最大力和工作频率（收缩速度）之间是否存在权衡？为了回答这些问题，我们将结合研究蜂鸟燃料的使用，运动学，神经肌肉控制（EMG）模式的自由盘旋蜂鸟与孤立的蜂鸟胸肌的收缩特性的研究，包括物种在一个范围内的身体质量与不同的wingbeat频率的研究。这些结果将增加我们对肌肉性能和高频率加油的限制的理解，并确定通常适用于所有运动肌肉的肌肉生理学各个方面之间的权衡。

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.