Concord Field Station, Department of Organismic and Evolutionary Biology, Harvard University, Bedford 01730, MA, USA
Department of Mechanical Engineering & Materials Science, Yale University, New Haven, CT 06520-8292, USA.
J Exp Biol. 2019 Dec 18;222(Pt 24):jeb205559. doi: 10.1242/jeb.205559.
Muscle function changes to meet the varying mechanical demands of locomotion across different gait and grade conditions. A muscle's work output is determined by time-varying patterns of neuromuscular activation, muscle force and muscle length change, but how these patterns change under different conditions in small animals is not well defined. Here, we report the first integrated force-length and activation patterns in rats, a commonly used small animal model, to evaluate the dynamics of two distal hindlimb muscles (medial gastrocnemius and plantaris) across a range of gait (walk, trot and gallop) and grade (level and incline) conditions. We use these data to explore how the pattern of force production, muscle activation and muscle length changes across conditions in a small quadrupedal mammal. As hypothesized, we found that the rat muscles show limited fascicle strains during active force generation in stance across gaits and grades, indicating that these distal rat muscles generate force economically but perform little work, similar to patterns observed in larger animals during level locomotion. Additionally, given differences in fiber type composition and variation in motor unit recruitment across the gait and grade conditions examined here for these muscles, the force-length behavior and neuromuscular activation data reported here can be used to validate improved two-element Hill-type muscle models.
肌肉功能会发生变化，以适应不同步态和坡度条件下运动的变化力学需求。肌肉的做功输出由时变的神经肌肉激活、肌肉力量和肌肉长度变化模式决定，但这些模式在小动物的不同条件下如何变化还没有得到很好的定义。在这里，我们报告了第一个在小动物模型（大鼠）中整合的力-长和激活模式，以评估两种远端后肢肌肉（内侧腓肠肌和比目鱼肌）在一系列步态（步行、小跑和疾驰）和坡度（水平和倾斜）条件下的动力学。我们使用这些数据来探讨小型四足哺乳动物在不同条件下的力量产生、肌肉激活和肌肉长度变化的模式。正如假设的那样，我们发现大鼠肌肉在站立时的主动力产生过程中，在各种步态和坡度下表现出有限的肌束应变，这表明这些远端大鼠肌肉在经济地产生力的同时做功很少，这与在较大动物在水平运动时观察到的模式相似。此外，考虑到这些肌肉在步态和坡度条件下的纤维类型组成和运动单位募集的差异，这里报告的力-长行为和神经肌肉激活数据可用于验证改进的双元素 Hill 型肌肉模型。
