Shortening velocity and power output of muscles that produce ballistic movements

缩短产生弹道运动的肌肉的速度和功率输出

• 批准号: 0240349
• 负责人: Kiisa Nishikawa
• 金额: $ 34.83万
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-06-01 至 2007-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0240349&HistoricalAwards=false
• 关键词: Shortening; velocity; power; output; muscles

New insights in biology have often come from studies of animals that exhibit some extreme of performance. In such animals, principles of function common to all animals are exaggerated, and are therefore observed and studied more readily. Ballistic tongue projection in toads represents one such extreme. During ballistic tongue projection, toad tongues can leave the mouth at accelerations of 2500 m/s2. Previous and ongoing research in the laboratories of these investigators has focused on elucidating mechanisms by which mouth opening muscles of toads produce the power required for this extremely rapid movement. The work in this project will focus on understanding the force-velocity relationships and power output of two muscles that are involved in powering ballistic movements: 1) the m. depressor mandibulae, which is solely responsible for mouth opening during tongue projection ; and 2) the m. semimembranosus, which along with other muscles, extends the hind limb during jumping. The proposed studies will use the classic load clamp or quick release technique to quantify the biphasic shortening behavior of these muscles during the transition from isometric tetanus to isotonic shortening. In the load clamp technique, an activated muscle is stimulated to develop tension while contracting against a load that prevents it from shortening. When the load is reduced, the muscle first shortens rapidly and then decelerates to a slower shortening velocity. In contrast to most recent studies which measure only the velocity of shortening during the slow phase, these investigators measured velocity of shortening during the initial fast phase as well. Four important new aspects of the shortening behavior of muscle have been discovered. During the fast phase: 1) shortening velocity can be high (up to nearly 100 times Vmax), and it differs between jaw and hind limb muscles; 2) external work performed contributes to total power output, although the magnitude of the contribution varies between the jaw and hind limb muscles; 3) shortening velocity increases with the duration of isometric pre-stimulation; and during the slow phase 4) shortening velocity also increases with the duration of isometric pre-stimulation, at least in some muscles. These results are consistent with a model in which a series elastic component within the sarcomere is stretched by the contractile elements during isometric tetanus, and the degree of stretch increases with the duration of isometric pre-stimulation. Preliminary data suggest that muscles differ adaptively in how kinetic energy is distributed between the fast and slow phases of shortening. A mechanism, such as phosphorylation of the thick and/or thin filaments, that controls the distribution of kinetic energy between the fast and slow phases would likely be important in controlling muscle power output during ballistic movements. The proposed studies will extend these preliminary studies. Specifically, the investigators will: 1) compare biphasic shortening of anuran jaw and hind limb muscles in species of anurans that differ in feeding and jumping performance; 2) quantify the effects of duration of isometric pre-stimulation and muscle length on biphasic shortening; and 3) examine the relationship between movement velocity and duration of muscle pre-activation in freely behaving animals. The proposed studies are likely to demonstrate: 1) that a significant amount of elastic potential energy, stored during isometric pre-stimulation, is converted to kinetic energy at the instant of release to isotonic shortening; and 2) that muscles differ in their strategies for distributing this kinetic energy between the fast and slow phases of shortening, thereby optimizing their power output during shorter vs. longer contractions. In these ways, the proposed studies have the potential to change our concept of how muscles shorten, especially at the high velocities that occur during ballistic movements.

生物学上的新见解往往来自对表现出某些极端行为的动物的研究。在这些动物身上，所有动物共有的功能原理都被夸大了，因此更容易被观察和研究。蟾蜍的弹道舌突就是这样一个极端。在弹道舌头投射过程中，蟾蜍舌头可以以2500米/秒的加速度离开口腔。在这些研究人员的实验室里，以前和正在进行的研究都集中在阐明蟾蜍张嘴肌肉产生这种极快速运动所需力量的机制上。这个项目的工作将集中于理解两种肌肉的力-速度关系和能量输出，这两种肌肉参与了弹道运动的动力：1)下颌骨下压肌，它在舌头投射时完全负责张嘴；2)半膜肌，它和其他肌肉一起，在跳跃时伸展后肢。拟议的研究将使用经典的负载钳或快速释放技术来量化这些肌肉在从等距破伤风到等张力缩短过渡期间的双相缩短行为。在负载夹紧技术中，激活的肌肉受到刺激而产生张力，同时对抗防止其缩短的负载收缩。当负荷减少时，肌肉首先迅速缩短，然后减速到一个较慢的缩短速度。与最近大多数研究只测量慢期的缩短速度相反，这些研究人员也测量了最初快期的缩短速度。已经发现了肌肉缩短行为的四个重要的新方面。在快速阶段：1)缩短速度可以很高（可达Vmax的近100倍），下颌和后肢肌肉的缩短速度不同；2)外部工作对总功率输出有贡献，尽管贡献的大小在颌骨和后肢肌肉之间有所不同；3)缩短速度随等长预刺激时间的延长而增加；在慢速阶段，缩短速度也随着等长预刺激的持续时间而增加，至少在某些肌肉中是这样。这些结果与一个模型是一致的，在这个模型中，肌节内的一系列弹性成分在等距破伤风期间被收缩元素拉伸，拉伸程度随着等距预刺激的持续时间而增加。初步数据表明，肌肉在快速和缓慢缩短阶段之间动能分配的适应性不同。一种机制，如粗丝和/或细丝的磷酸化，控制着快速和缓慢阶段之间的动能分布，可能对控制弹道运动期间的肌肉力量输出很重要。拟议的研究将扩展这些初步研究。具体而言，研究人员将：1)比较不同摄食和跳跃能力的无尾猿两相下颌和后肢肌肉的缩短；2)量化等长预刺激持续时间和肌肉长度对双相缩短的影响；3)研究自由行为动物运动速度与肌肉预激活持续时间的关系。拟议的研究可能会证明：1)在等长预刺激期间储存的大量弹性势能在释放到等压缩短的瞬间转化为动能；2)肌肉在快速和缓慢收缩阶段分配动能的策略不同，从而在短收缩和长收缩期间优化其能量输出。在这些方面，拟议的研究有可能改变我们对肌肉如何缩短的概念，特别是在高速弹道运动中发生的运动。