Skeletal muscle has a broad range of biomechanical functions, including power generation and energy absorption. These roles are underpinned by the force–velocity relationship, which comprises two distinct components: a concentric and an eccentric force–velocity relationship. The concentric component has been extensively studied across a wide range of muscles with different muscle properties. However, to date, little progress has been made in accurately characterising the eccentric force–velocity relationship in mammalian muscle with varying muscle properties. Consequently, mathematical models of this muscle behaviour are based on a poorly understood phenomenon. Here, we present a comprehensive assessment of the concentric force–velocity and eccentric force–velocity relationships of four mammalian muscles (soleus, extensor digitorum longus, diaphragm and digastric) with varying biomechanical functions, spanning three orders of magnitude in body mass (mouse, rat and rabbits). The force–velocity relationship was characterised using a hyperbolic-linear equation for the concentric component a hyperbolic equation for the eccentric component, at the same time as measuring the rate of force development in the two phases of force development in relation to eccentric lengthening velocity. We demonstrate that, despite differences in the curvature and plateau height of the eccentric force–velocity relationship, the rates of relative force development were consistent for the two phases of the force–time response during isovelocity lengthening ramps, in relation to lengthening velocity, in the four muscles studied. Our data support the hypothesis that this relationship depends on cross-bridge and titin activation. Hill-type musculoskeletal models of the eccentric force–velocity relationship for mammalian muscles should incorporate this biphasic force response.

骨骼肌具有广泛的生物力学功能，包括发电和能量吸收。这些作用以力-速度关系为基础，力-速度关系由两个不同的组成部分组成：同心和偏心力-速度关系。同心组件已在具有不同肌肉特性的各种肌肉中进行了广泛研究。然而，迄今为止，在准确表征具有不同肌肉特性的哺乳动物肌肉的偏心力-速度关系方面几乎没有取得进展。因此，这种肌肉行为的数学模型是基于一种人们知之甚少的现象。在这里，我们对具有不同生物力学功能的四种哺乳动物肌肉（比目鱼肌、趾长伸肌、膈肌和二腹肌）的同心力-速度和偏心力-速度关系进行了全面评估，跨越了体重的三个数量级（小鼠、大鼠和兔子）。使用同心部件的双曲线性方程和偏心部件的双曲方程来表征力-速度关系，同时测量力发展的两个阶段中与偏心延长速度相关的力发展速率。我们证明，尽管偏心力-速度关系的曲率和平台高度存在差异，但等速延长斜坡期间力-时间响应的两个阶段的相对力发展速率与延长速度相关，在研究了四块肌肉。我们的数据支持这样的假设：这种关系取决于跨桥和肌联蛋白激活。哺乳动物肌肉偏心力-速度关系的山型肌肉骨骼模型应包含这种双相力响应。