Neural network model for control of muscle force based on the size principle of motor unit

A neural-network model consisting of a single motor cortex output cell, alpha motoneurons, Renshaw cells, and muscle units is proposed. Linear relations between motor cortex output and force output that were observed in monkeys and firing rate versus force relations in human skeletal muscles are explained by computer simulations. It is suggested that Renshaw recurrent inhibition has the effect of linearizing the gain between motor cortex output and force output, and it is confirmed that the orderly recruitment of motor units is governed by unit size in accordance with a classical observation. The model appears to represent a fundamental neural mechanism of force control because both firing rates and forces calculated from the model agree with experimental data in humans and monkeys.>