E5 Neuromuscular Control

Title

The central and peripheral nervous system controls muscle activation by modulating the firing rate of motor units (MUs) and recruiting additional MUs. Each UM is an alpha motor neuron and all the muscle fibers it innervates; Henneman's principle states that MUs are recruited in ascending order of size (small-slow first, large-fast for maximum strength). The EMG (electromyography) signal reflects the spatial and temporal sum of the action potentials of the active MUs. Muscle strength can be modeled as the product of normalized neural activation (0-1) and maximal force. The stretch reflex (monosynaptic reflex arc, latency ~40 ms in the lower limb) provides proprioceptive feedback that stabilizes the joints during ground contact. Total reaction time (neural + electromechanical) limits the speed of force generation in impact situations. Coactivation of antagonist muscles increases joint stiffness at the expense of reducing net force and metabolic efficiency.

ID:444