WordNet

an automatic instinctive unlearned reaction to a stimulus (同)reflex response, reflex action, instinctive reflex, innate reflex, inborn reflex, unconditioned_reflex, physiological reaction
the 8th letter of the Roman alphabet (同)h
(of leaves) bent downward and outward more than 90 degrees

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反射(刺激に対する無意識の反応) / 《複数形で》反射的な動き / (光などの)反射,反射光;映像 / 反射性の / (カメラが)レフ鋼の,反射型の
hydrogenの化学記号
鉛筆の硬度 / 《俗》heroin

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/12/06 17:11:14」(JST)

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The H-reflex (or Hoffmann's 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). 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 an F-wave, compromising the results), and an EMG set, to record the muscle response. That response is usually a clear wave, called H-wave, 28-35 ms after the stimulus, not to be confused with an F-wave. An M-wave, an early response, occurs 3-6 ms after the onset of stimulation. The H and F-waves are later responses. As the stimulus increases, the amplitude of the F-wave increases only slightly, and the H-wave decreases, and at supramaximal stimulus, the H-wave will disappear. The M-wave does the opposite of the H-wave. As the stimulus increases the M-wave increases. There is a point of minimal stimulus where the M-wave is absent and the H-wave is maximal.

H-reflex is analogous to the mechanically induced spinal stretch reflex (for example, knee jerk reflex). "The primary difference between the H-reflex and the spinal stretch reflex is that the H-reflex bypasses the muscle spindle, and, therefore, is a valuable tool in assessing modulation of monosynaptic reflex activity in the spinal cord."^[1] Although stretch reflex gives just qualitative information about muscle spindles and reflex 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 amplitudes measured by EMG are shown to decrease significantly with applied pressure such as massage and tapping to the cited muscle. The amount of decrease seems to be dependent on the force of the pressure, with higher pressures resulting in lower H-reflex amplitudes. H-reflex levels return to baseline immediately after pressure is released except in high pressure cases which had baseline levels returned within the first 10 seconds.^[2]

After about 5 days in zero gravity, for instance in orbit around Earth, the h-reflex diminishes significantly. It is generally assumed that this is due to a marked reduction in the excitability of the spinal cord in zero gravity. Once back on Earth, a marked recovery occurs during the first day, but it can take up to 10 days to return to normal. The H-reflex was the first medical experiment completed on the International Space Station.^[3]^[4]

History

It was first described by Paul Hoffmann (hence the name) in 1910.^[5]

References

^ Palmieri RM, Ingersoll CD, Hoffman MA (July 2004). "The Hoffmann Reflex: Methodologic Considerations and Applications for Use in Sports Medicine and Athletic Training Research". J Athl Train. 39 (3): 268–77. PMC 522151. PMID 16558683.
^ Goldberg, Joanne; Sullivan, Seaborne (1992). "The Effect of Two Intensities of Massage on H-Reflex Amplitude". Journal of the American Physical Therapy Association. 72: 449–457.
^ http://www.asc-csa.gc.ca/eng/sciences/hreflex.asp
^ http://www.nasa.gov/mission_pages/station/science/experiments/H-Reflex.html
^ Hoffmann P. Beitrag zur Kenntnis der menschlichen Reflexe mit besonderer Berucksichtigung der elektrischen Erscheinungen. Arch Anat Physiol. 1910;1:223–246.

External links

H-Reflex at the US National Library of Medicine Medical Subject Headings (MeSH)

UpToDate Contents

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English Journal

Effects of 12-week Tai Chi training on soleus H-reflex and muscle strength in older adults: a pilot study.

Chen YS, Crowley Z, Zhou S, Cartwright C.SourceSchool of Health and Human Sciences, Southern Cross University, P.O. Box 157, Lismore, NSW, 2480, Australia.
European journal of applied physiology.Eur J Appl Physiol.2012 Jun;112(6):2363-8. Epub 2011 Sep 27.
The purpose of this study was to determine the effects of 12-week Tai Chi (TC) training on the soleus (SOL) H-reflex modulation and plantarflexion muscle strength in older adults. Twenty volunteers were assigned into training (N = 14; 72.2 ± 3.7 years of age) and control (N = 6; 74.2 ± 6.
PMID 21947456

Spinal and cortical activity-dependent plasticity following learning of complex arm movements in humans.

Winkler T, Mergner B, Szecsi J, Bender A, Straube A.SourceDepartment of Neurology, Klinikum der Ludwig-Maximilians Universität München, Marchioninistr. 15, 81377, Munich, Germany, tobias.winkler@med.uni-muenchen.de.
Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale.Exp Brain Res.2012 Jun;219(2):267-74. Epub 2012 Apr 4.
Activity-dependent plasticity is a fundamental requirement for human motor learning, which takes place at several stages of the motor system and involves various mechanisms in neuronal circuitry. Here, we investigate parameters of cortical and spinal excitability before and immediately after a singl
PMID 22476217