Nature has solved the problem of controlling legged locomotion many thousands of times in animals exhibiting an enormous variety of neuromechanical structures. Control systems features that are common to nearly all species include feedback control of limb displacement and force and feedforward generation of motor patterns by neural networks within the central nervous system (Central Pattern Generators: CPGs). Here we review the components of locomotor control systems, with a focus on mammalian animals including humans. We then propose a generalized model of reflex control and discuss the mathematical functions that describe the properties of the components of a spinal stretch reflex model.Reflex model of neuromuscular control. Here we provide and discuss the mathematical functions for the components in the reflex model presented in Subchapter 6.6. These include functions that describe muscle intrinsic properties (excitation-contraction coupling, force-velocity and orce-length curves) and sensory receptor models (muscle spindle responses to length changes and fusimotor drive, Golgi tendon organ responses to changes in muscle force).