H-reflex 1771213 210958289 2008-05-08T03:31:02Z Chris the speller 525927 sp, hyphen The '''H-reflex''' is a [[reflectory reaction]] of muscles after [[electrical]] stimulation of sensory fibers ([[Ia afferent]]s stemming from [[muscle spindles]]) in their innervating nerves (for example, those located behind the [[knee]]). The H-reflex test is performed using an electric stimulator, which gives usually a square-wave current of short duration and small amplitude (higher stimulations might involve alpha fibers, causing a M-wave, compromising the results), and an [[EMG]] set, to record the muscle response. That response is usually a clear wave, called H-wave, 50 ms after the stimulus, not to be confused with M-wave at 25-30 ms, wich might appear in too intense stimulations. 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. Although stretch reflex gives just qualitative information about muscle spindles and relfex arch activity; if the purpose of the test to compare performances from different subjects, H-reflex should be used. In that case, in fact, latencies (ms) and amplitudes (mV) of H-wave can be compared. H-reflex is used to assess fitness of [[astronaut]]s. H-reflex was the first medical experiment completed on the [[International Space Station]]. ==History== It was first described by Paul Hoffmann (hence the name) in 1910. <ref>Hoffmann P. Beitrag zur Kenntnis der menschlichen Reflexe mit besonderer Berucksichtigung der elektrischen Erscheinungen. Arch Anat Physiol. 1910;1:223–246.</ref> == See also == * [[Motor reflex]] * [[Tendon reflex]] * [[Achilles reflex]] * [[Pupillary reflex]] * [[Tonic vibration reflex]] ==External links== * {{MeshName|H-Reflex}} == References == <references/> {{Reflex}} [[de:H-Reflex]] [[Category:Reflexes]]