Modeling Gait Muscle-Reflexes Through Hindlimb Characterization in Rodents

Abstract

The complexity of gait modeling ranges from simple models that represent the leg as two linear springs to more complex ones that comprise muscle-tendons and spinal muscle-reflexes. However, the more complex models fail to have a strong empirical basis for muscle-reflex definition and function. To garner stronger evidence for the reflex component of muscle function in gait, we modeled gait muscle-reflexes through experimental limb characterization in rodents. We designed and implemented an animal skin port with multiple electrodes to measure the electromyography, muscle fascicle length, and muscle force. We conducted rat surgeries that implanted this skin port, and used the device to collect in vivo data through various terrain during walking trials. From collaborator’s in vivo data (n = 4 rodents), we implemented multiple linear reflex models with an r² ranging from 0.75 to 0.87 between measured and predicted muscle activations, consistent with predictions from muscle models found in the literature. We also found that the dominant contributor to the reflex in the medial gastrocnemius muscle is a positive force feedback. Future works could explore a similar paradigm in the tibialis anterior muscle, an antagonist to the medial gastrocnemius muscle, and explore higher order nonlinear muscle-reflex models.