The intersection of ground reaction forces near a point above the center of mass has been observed in computer simulation models and human walking experiments. Observed so ubiquitously, the intersection point (IP) is commonly assumed to provide postural stability for bipedal walking. In this study, we challenge this assumption by questioning if walking without an IP is possible. Deriving gaits with a neuromuscular reflex model through multi-stage optimization, we found stable walking patterns that show no signs of the IP-typical intersection of ground reaction forces. The non-IP gaits found are stable and successfully rejected step-down perturbations, which indicates that an IP is not necessary for locomotion robustness or postural stability. A collision-based analysis shows that non-IP gaits feature center of mass (CoM) dynamics with vectors of the CoM velocity and ground reaction force increasingly opposing each other, indicating an increased mechanical cost of transport. Although our computer simulation results have yet to be confirmed through experimental studies, they already indicate that the role of the IP in postural stability should be further investigated. Moreover, our observations on the CoM dynamics and gait efficiency suggest that the IP may have an alternative or additional function that should be considered.

翻译：地面反作用力在质心上方的某点附近相交的现象，已在计算机仿真模型和人类行走实验中被观测到。由于这种观测极为普遍，该交点（IP）通常被认为能为双足行走提供姿态稳定性。本研究通过质疑无IP行走的可能性来挑战这一假设。我们利用多阶段优化从神经肌肉反射模型中推导步态，发现了稳定的行走模式，这些模式中完全不存在IP典型的地面反作用力交会特征。所发现的非IP步态具有稳定性，并能成功抵抗下台阶扰动，表明IP对运动鲁棒性或姿态稳定性并非必需。基于碰撞的分析显示，非IP步态的质心动力学特征表现为质心速度矢量与地面反作用力矢量的反向对抗程度增加，表明机械运输成本上升。尽管我们的计算机仿真结果尚需实验验证，但已显示应进一步探究IP在姿态稳定性中的作用。此外，关于质心动力学与步态效率的观察表明，IP可能存在替代性或附加性功能值得关注。