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]]