H-reflex

The H-reflex is a reflectory reaction of muscles after electrical stimulation of sensory fibers (Ia afferents stemming from muscle spindles) in their innervating nerves (for example, those located behind the knee). It was first described by Paul Hoffmann (hence the name) in 1910.

H-reflex is analogous to the mechanically induced spinal stretch reflex (for example, knee jerk reflex) because both cases muscle-spindle innervating fibers are activated.

H-reflex is used to assess fitness of astronauts. H-reflex was the first medical experiment completed on the International Space Station.