Fueling and performance in a high speed locomotor muscle

这项研究考察了运动肌肉的能量和机械性能随着身体大小和肌肉工作频率的变化而变化的一些方式。蜂鸟独特的盘旋飞行是脊椎动物所使用的最耗能和最昂贵的运动形式。胸肌和胸骨上肌分别负责驱动蜂鸟的下拍和上拍，它们的工作频率与身体质量成反比，小型蜂鸟的运动肌肉工作频率是所有脊椎动物中最快的。过去的研究已经揭示了一些解剖和生化特征，使蜂鸟胸肌能够实现高速率的有氧代谢。然而，关于悬停过程中被氧化的燃料的来源、肌肉性能的调节机制以及高速运动肌肉的收缩特性的量化，包括这些特性如何随着身体质量或肌肉工作频率的变化而变化的许多问题，仍然没有得到回答。这项提案中的研究将解决三个主要问题：1)不同体型和悬停代谢率的蜂鸟在运动中使用新摄取的燃料的能力与内源性燃料的能力有何不同？2)胸肌的神经肌肉控制模式如何与翼拍频率有关？3)蜂鸟胸肌的最大作用力和工作频率(收缩速度)之间是否存在权衡？为了回答这些问题，我们将结合对自由盘旋蜂鸟的燃料使用、运动学和神经肌肉控制(EMG)模式的研究，以及对孤立的蜂鸟胸肌收缩特性的研究，包括研究不同翼拍频率的不同体重范围内的物种。研究结果将增加我们对肌肉表现和高频补充能量的限制的理解，并确定肌肉生理学的各个方面之间的权衡，这些方面普遍适用于所有运动肌肉。

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.