What is H-reflex in EMG? The H reflex is basically an electrophysiologically recorded Achilles muscle stretch reflex. It is performed by stimulating the tibial nerve in the popliteal fossa. From there, the stimulus goes proximally
What is H-reflex in EMG?
The H reflex is basically an electrophysiologically recorded Achilles muscle stretch reflex. It is performed by stimulating the tibial nerve in the popliteal fossa. From there, the stimulus goes proximally through the reflex arc at that spinal segment, then distally from the anterior horn cell and the motor nerve.
What does the H-reflex do?
The H-reflex can be used to assess changes in motoneuron pool reflex excitability. This reflex, also known as the Hoffmann reflex, is an electrically stimulated reflex that excites the muscle spindles Ia afferents.
What is H wave reflex?
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). An M-wave, an early response, occurs 3-6 ms after the onset of stimulation.
What is the difference between F wave and H-reflex?
Unlike the H-reflex, the F-wave is always preceded by a motor response and its amplitude is rather small, usually in the range of 0.2-0.5 mv. The F-wave is a variable response and is obtained infrequently after nerve stimulation.
Why does the H wave disappear at high stimulation levels?
The stimulus intensity is set at 0 and gradually increased until maximum Hoffmann reflex amplitude and maximum muscle response amplitude are achieved. The reason for the disappearance of the H-reflex is an effect known as antidromic collision.
What does abnormal F wave mean?
The F-wave is a compound action potential evoked by supramaximal antidromic stimulation of a motor nerve16). The absence or slowing of F-waves may be an isolated conduction abnormality, especially during the early stages of illness17).
What is a normal F wave?
Maximum normal F wave latency for median nerve was 25.7 ms for women and 28.5 ms for men with stimulation at the wrist. It was 23 ms for women and 25 ms for men with stimulation at the elbow. Maximum normal F wave latency for ulnar nerve was 26.45 ms for women and 28.9 ms for men with stimulation at the wrist.
What causes F waves?
The F wave is a late CMAP evoked intermittently from a muscle by a supramaximal electrical stimulus to the nerve, and it is due to antidromic activation (backfiring) of alpha motor neurons. F waves can be elicited from practically all distal motor nerves.
What is a long loop reflex?
Definition. Long loop reflexes are automatic motor responses to somatosensory stimuli that are believed to operate via the cerebral cortex, hence the term transcortical reflexes.