How small deviations in kinematics and body form dictate muscle performances in the finely tuned avian downstroke

Avian takeoff requires peak pectoralis muscle power to generate sufficient aerodynamic force during the downstroke. Subsequently the much smaller supracoracoideus recovers the wing during the upstroke. How the pectoralis work loop is tuned to power flight is unclear. We integrate wingbeat-resolved muscle, kinematic and aerodynamic recordings in vivo with a new mathematical model to disentangle how the pectoralis muscle overcomes wing inertia and generates aerodynamic force during takeoff in doves. Doves reduce the incidence of their wing mid-downstroke to efficiently generate aerodynamic force, resulting in an aerodynamic power dip, that allows transferring excess pectoralis power into tensioning the supracoracoideus tendon to assist the upstroke—improving the pectoralis work loop efficiency simultaneously. Integrating extant bird data, our model shows how the pectoralis of birds with faster wingtip speed need to generate proportionally more power. Finally, birds with disproportionally ...

鸟类起飞过程中，需让胸肌（pectoralis muscle）达到峰值功率，以在下挥冲程（downstroke）阶段生成足够的气动力。随后，体积小得多的上乌喙肌（supracoracoideus muscle）会在翅部上挥冲程（upstroke）中完成翅的复位动作。目前学界尚未明确胸肌工作循环（pectoralis work loop）如何适配飞行供能需求。本研究将鸽类起飞时，同步于每一次翅拍的活体（in vivo）肌肉、运动学及气动力记录数据，与全新的数学模型相结合，以厘清胸肌如何克服翅部惯性，并在起飞阶段产生气动力。鸽类通过降低翅部下冲程中期的摆动幅度以高效生成气动力，该过程会形成气动力功率凹陷，从而可将多余的胸肌功率转移用于张紧上乌喙肌肌腱（supracoracoideus tendon）以辅助上挥冲程，同时提升胸肌工作循环的效率。整合现生鸟类（extant bird）数据集后，本研究模型揭示：翅尖运动速度更快的鸟类，其胸肌需按比例输出更高的功率。最后，具有不成比例的……