What are the H reflexes in nerve conduction studies?

Updated: Aug 20, 2018
  • Author: Stephen Kishner, MD, MHA; Chief Editor: Jonathan P Miller, MD  more...
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Answer

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. It can be recorded over the soleus or gastrocnemius muscles. The H reflex is most commonly used to evaluate for an S1 radiculopathy or to distinguish from an L5 radiculopathy.

Needle EMG is used to assess both nerve and muscle function. A small-diameter monopolar pin or coaxial needle is placed into a muscle to evaluate insertional activity, resting activity, voluntary recruitment, morphology, and size of motor units, as well as motor unit recruitment. The needle electrode examination provides valuable information about the electrical characteristics of individual muscle fibers and motor units, as well as the integrity and innervation of muscle fibers. This test can be uncomfortable for the patient.


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