Data from: Integrating gastrocnemius force-length properties, in vivo activation, and operating lengths reveals how Anolis deal with ecological challenges

A central question in biology is how animals successfully behave under complex natural conditions. Although changes in locomotor behaviour, motor control, and force production in relation to incline are commonly examined, a wide range of other factors, including a range of perch diameters, pervades arboreal habitats. Moving on different substrate diameters requires considerable alteration of body and limb posture, likely causing significant shifts in the lengths of the muscle-tendon units powering locomotion. Thus, how substrate shape impacts in vivo muscle function remains an important, but neglected question in ecophysiology. Here, we used high-speed videography, electromyography, in situ contractile experiments, and morphology to examine gastrocnemius muscle function during arboreal locomotion in the Cuban knight anole, (Anolis equestris). The gastrocnemius contributes more to the propulsive effort on broad surfaces than on narrow surfaces. Surprisingly, substrate inclination affected the relationship between the maximum potential force and fibre recruitment; the trade-off that was present between these variables on horizontal conditions became a positive relationship on inclined surfaces. Finally, the biarticular nature of the gastrocnemius allows it to generate force isometrically, regardless of condition, despite the fact that the tendons are incapable of stretching during cyclical locomotion. Our results emphasize the importance of considering ecology and muscle function together, and the necessity of examining both mechanical and physiological properties of muscles to understand how animals move in their environment.

生物学领域的核心议题之一，是动物如何在复杂的自然环境中顺利完成各类行为活动。尽管学界常针对坡度相关的运动行为、运动控制及力量产出变化开展研究，但树栖生境中还存在诸多其他影响因素，其中就涵盖不同直径的栖木基质。在不同直径的基质上移动时，动物的身体与肢体姿势需要大幅调整，这大概率会显著改变驱动运动的肌-腱单元（muscle-tendon units）的长度。因此，基质形态如何影响在体（in vivo）肌肉功能，仍是生态生理学领域一个重要却长期被忽视的科学问题。
本研究以古巴骑士安乐蜥（Anolis equestris）为实验对象，结合高速摄像术（high-speed videography）、肌电图（electromyography, EMG）、原位收缩实验（in situ contractile experiments）与形态学分析手段，探究了其树栖运动过程中腓肠肌的功能表现。相较于狭窄栖面，腓肠肌在宽阔基质上对运动推进力的贡献更为显著。令人意外的是，基质坡度会改变最大潜在力量与肌纤维募集之间的关联：在水平条件下二者呈现权衡关系，而在倾斜基质上则变为正相关关系。
此外，腓肠肌的双关节结构使其能够在任意实验条件下产生等长收缩力量，即便其肌腱在周期性运动过程中无法被拉伸。本研究结果强调了将生态学与肌肉功能协同考量的重要性，同时也指明，若要深入理解动物如何在其所处环境中移动，必须同时考察肌肉的力学与生理学双重特性。