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.

明确肢体关节的力学输出，对于理解行走等复杂运动行为的调控机制至关重要。就昆虫行走而言，单关节控制的神经基础（neural infrastructure）已有详尽阐释。然而，目前仍缺乏以时变关节扭矩（time-varying joint torques）形式呈现的运动输出细节描述。本研究通过测定竹节虫（stick insect）的关节扭矩，旨在明确腿部关节在躯体高度调控与推进过程中的功能。研究通过记录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）来计算关节扭矩。本研究证实，尽管竹节虫在形态学特征与姿势上存在显著差异，但其关节的功能分化模式与其他昆虫模式系统高度相似。推进力由基节-转节关节（coxa-trochanter joint）处的强下压扭矩产生，而非回缩扭矩或屈伸扭矩（flexion/extension torques）。胸-基节关节（thorax-coxa joint）与股-胫节关节（femur-tibia joint）处的扭矩方向，往往与前后向力（fore-aft forces）及关节运动方向相反。这表明存在一种依赖于姿势的调控机制：该机制可抵消躯体载荷导致的腿部塌陷，并调整合力矢量（resultant force vector）方向，使得强下压扭矩能够同时调控躯体高度与推进力。本研究结果与其他行走、跳跃及飞行昆虫的推进机制相符，同时对现有昆虫行走控制模型提出了挑战。