Data from: Joint torques in a freely walking insect reveal distinct functions of leg joints in propulsion and posture control

Determining the mechanical output of limb joints is critical for understanding the control of complex motor behaviours such as walking. In the case of insect walking, the neural infrastructure for single-joint control is well described. However, a detailed description of the motor output in form of time-varying joint torques is lacking. Here, we determine joint torques in the stick insect to identify leg joint function in the control of body height and propulsion. Torques were determined by measuring whole-body kinematics and ground reaction forces in freely walking animals. We demonstrate that despite strong differences in morphology and posture, stick insects show a functional division of joints similar to other insect model systems. Propulsion was generated by strong depression torques about the coxa-trochanter joint, not by retraction or flexion/extension torques. Torques about the respective thorax-coxa and femur-tibia joints were often directed opposite to fore-aft forces and joint movements. This suggests a posture-dependent mechanism that counteracts collapse of the leg under body load and directs the resultant force vector such that strong depression torques can control both body height and propulsion. Our findings parallel propulsive mechanisms described in other walking, jumping, and flying insects and challenge current control models of insect walking.

确定肢体关节的力学输出，对于理解行走等复杂运动行为的控制机制至关重要。针对昆虫行走领域，单关节控制的神经基础已有充分阐释，但以时变关节扭矩（time-varying joint torques）形式呈现的运动输出详细描述仍存在空白。本研究以竹节虫（stick insect）为研究对象，通过测定自由行走个体的全身运动学（whole-body kinematics）与地面反作用力（ground reaction forces），明确其腿部关节在身体高度控制与推进过程中的功能。研究结果显示，尽管在形态学（morphology）与姿势（posture）上存在显著差异，但竹节虫的关节功能划分模式与其他昆虫模型系统高度相似。推进力由基节-转节关节（coxa-trochanter joint）的强下压扭矩驱动，而非依靠回缩或屈伸扭矩。胸-基节关节（thorax-coxa）与股-胫节关节（femur-tibia）产生的扭矩，其方向通常与前后向力（fore-aft forces）及关节运动方向相反。这表明存在一种依赖姿势的调节机制，可抵消身体载荷下腿部的塌陷趋势，并调整合力矢量（resultant force vector）的方向，使得强下压扭矩能够同时实现身体高度控制与推进功能。本研究发现与其他行走、跳跃及飞行昆虫的推进机制（propulsive mechanisms）相符，同时对当前主流的昆虫行走控制模型（control models）提出了挑战。