McGowan C P, Baudinette R V, Biewener A A
Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
J Exp Biol. 2005 Jan;208(Pt 1):41-53. doi: 10.1242/jeb.01305.
Measurements of joint work and power were determined using inverse dynamics analysis based on ground reaction force and high-speed video recordings of tammar wallabies as they decelerated and accelerated while hopping over a force platform on level ground. Measurements were obtained over a range of accelerations ranging from -6 m s(-2) to 8 m s(-2). The goal of our study was to determine which joints are used to modulate mechanical power when tammar wallabies change speed. From these measurements, we also sought to determine which hind limb muscle groups are the most important for producing changes in mechanical work. Because our previous in vivo analyses of wallaby distal muscle function indicated that these muscle-tendon units favor elastic energy savings and perform little work during steady level and incline hopping, we hypothesized that proximal muscle groups operating at the hip and knee joint are most important for the modulation of mechanical work and power. Of the four hind limb joints examined, the ankle joint had the greatest influence on the total limb work, accounting for 89% of the variation observed with changing speed. The hip and metatarsophalageal (MP) joints also contributed to modulating whole limb work, but to a lesser degree than the ankle, accounting for 28% (energy production) and -24% (energy absorption) of the change in whole limb work versus acceleration, respectively. In contrast, the work produced at the knee joint was independent of acceleration. Based on the results of our previous in vivo studies and given that the magnitude of power produced at the ankle exceeds that which these muscles alone could produce, we conclude that the majority of power produced at the ankle joint is likely transferred from the hip and knee joints via proximal bi-articular muscles, operating in tandem with bi-articular ankle extensors, to power changes in hopping speed of tammar wallabies. Additionally, over the observed range of performance, peak joint moments at the ankle (and resulting tendon strains) did not increase significantly with acceleration, indicating that having thin tendons favoring elastic energy storage does not necessarily limit a tammar wallaby's ability to accelerate or decelerate.
基于地面反作用力和高速视频记录，通过逆动力学分析确定了短尾矮袋鼠在水平地面上越过测力平台减速和加速时的关节功和功率测量值。测量是在从-6 m s(-2)到8 m s(-2)的一系列加速度范围内进行的。我们研究的目的是确定短尾矮袋鼠改变速度时哪些关节用于调节机械功率。从这些测量中，我们还试图确定哪些后肢肌肉群对于产生机械功的变化最为重要。因为我们之前对袋鼠远端肌肉功能的体内分析表明，这些肌肉-肌腱单元有利于节省弹性能量，并且在稳定的水平和倾斜跳跃过程中做功很少，所以我们假设在髋关节和膝关节处起作用的近端肌肉群对于机械功和功率的调节最为重要。在所检查的四个后肢关节中，踝关节对整个肢体功的影响最大，占速度变化时观察到的变化的89%。髋关节和跖趾（MP）关节也有助于调节整个肢体功，但程度小于踝关节，分别占整个肢体功相对于加速度变化的28%（能量产生）和-24%（能量吸收）。相比之下，膝关节产生的功与加速度无关。基于我们之前体内研究的结果，并且鉴于踝关节产生的功率大小超过了这些肌肉单独所能产生的功率，我们得出结论，踝关节产生的大部分功率可能是通过近端双关节肌肉从髋关节和膝关节转移而来的，这些肌肉与双关节踝关节伸肌协同作用，为短尾矮袋鼠跳跃速度变化提供动力。此外，在所观察到的性能范围内，踝关节处的峰值关节力矩（以及由此产生的肌腱应变）并未随着加速度的增加而显著增加，这表明具有有利于弹性能量储存的细肌腱不一定会限制短尾矮袋鼠加速或减速的能力。
