Peplowski M M, Marsh R L
Department of Biology, Northeastern University, Boston, MA 02115, USA.
J Exp Biol. 1997 Nov;200(Pt 22):2861-70. doi: 10.1242/jeb.200.22.2861.
It has been suggested that small frogs use a catapult mechanism to amplify muscle power production during the takeoff phase of jumping. This conclusion was based on an apparent discrepancy between the power available from the hindlimb muscles and that required during takeoff. The present study provides integrated data on muscle contractile properties, morphology and jumping performance that support this conclusion. We show here that the predicted power output during takeoff in Cuban tree frogs Osteopilus septentrionalis exceeds that available from the muscles by at least sevenfold. We consider the sartorius muscle as representative of the bulk of the hindlimb muscles of these animals, because this muscle has properties typical of other hindlimb muscles of small frogs. At 25 degrees C, this muscle has a maximum shortening velocity (Vmax) of 8.77 +/- 0.62 L0 s-1 (where L0 is the muscle length yielding maximum isometric force), a maximum isometric force (P0) of 24.1 +/- 2.3 N cm-2 and a maximum isotonic power output of 230 +/- 9.2 W kg-1 of muscle (mean +/- S.E.M.). In contrast, the power required to accelerate the animal in the longest jumps measured (approximately 1.4 m) is more than 800 W kg-1 of total hindlimb muscle. The peak instantaneous power is expected to be twice this value. These estimates are probably conservative because the muscles that probably power jumping make up only 85% of the total hindlimb muscle mass. The total mechanical work required of the muscles is high (up to 60 J kg-1), but is within the work capacities predicted for vertebrate skeletal muscle. Clearly, a substantial portion of this work must be performed and stored prior to takeoff to account for the high power output during jumping. Interestingly, muscle work output during jumping is temperature-dependent, with greater work being produced at higher temperatures. The thermal dependence of work does not follow from simple muscle properties and instead must reflect the interaction between these properties and the other components of the skeletomuscular system during the propulsive phase of the jump.
有人提出，小型青蛙在跳跃的起跳阶段会使用弹射机制来放大肌肉力量的产生。这一结论是基于后肢肌肉可提供的力量与起跳时所需力量之间明显的差异得出的。本研究提供了关于肌肉收缩特性、形态和跳跃性能的综合数据，支持了这一结论。我们在此表明，古巴树蛙（Osteopilus septentrionalis）起跳时预测的功率输出比肌肉可提供的功率至少高出七倍。我们将缝匠肌视为这些动物后肢大部分肌肉的代表，因为该肌肉具有小型青蛙其他后肢肌肉的典型特性。在25摄氏度时，这块肌肉的最大缩短速度（Vmax）为8.77±0.62 L0 s-1（其中L0是产生最大等长力的肌肉长度），最大等长力（P0）为24.1±2.3 N cm-2，最大等张功率输出为230±9.2 W kg-1肌肉（平均值±标准误）。相比之下，在测量的最长跳跃（约1.4米）中加速动物所需的功率超过了整个后肢肌肉800 W kg-1。峰值瞬时功率预计是这个值的两倍。这些估计可能较为保守，因为可能为跳跃提供动力的肌肉仅占后肢肌肉总质量的85%。肌肉所需的总机械功很高（高达60 J kg-1），但仍在脊椎动物骨骼肌预测的做功能力范围内。显然，为了满足跳跃时的高功率输出，这项工作的很大一部分必须在起跳前完成并储存。有趣的是，跳跃过程中肌肉的功输出与温度有关，在较高温度下会产生更多的功。功的热依赖性并非源于简单的肌肉特性，而是必须反映这些特性与骨骼肌肉系统其他组成部分在跳跃推进阶段的相互作用。
