# A spinal network of proprioceptive reflexes can produce a variety of bipedal gaits

## TL;DR

A simple spinal reflex system can generate various natural bipedal gaits, suggesting proprioceptive reflexes play a key role in movement control.

## Contribution

A fixed-gain reflex controller is shown to produce diverse gaits without rhythmic inputs or state machines.

## Key findings

- The reflex controller generates walking, hopping, and running gaits in multiple directions and speeds.
- Natural gaits emerge without high-level control or modulated feedback gains.
- The model suggests proprioceptive reflexes are more flexible and essential for locomotion than previously thought.

## Abstract

Proprioception is crucial for movement, yet the role of proprioceptive reflexes in legged locomotion is still poorly understood. While previous simulation studies have shown great potential for reflex-based control strategies, these controllers are typically geared to specific gaits, using hand-crafted feedback pathways that are linked to specific gait phases. In this work, we explore the control capabilities of a simple reflex controller that consists of only homonymous and antagonistic length and force feedback pathways with constant gains. This control model can be considered a highly simplified subset of spinal control rather than an attempt to emulate all spinal control functions. Despite its simplicity, we found our control framework capable of producing a wide variety of natural gaits, including walking and hopping, forwards and backwards, and running in different variations and at different velocities – without requiring any rhythmic inputs or high-level state machines modulating the feedback gains. Our work highlights the important role and flexibility of proprioceptive reflexes and suggests a necessary re-evaluation of their role in locomotion. Due to its simplicity and flexibility, our control framework provides a solid basis for the development of higher-level neuromuscular control systems.

A spinal reflex controller with fixed-gain muscle force and length feedback can generate a wide range of natural gaits, offering insight into how proprioceptive reflexes may contribute to locomotor control.