Role of the H reflex in S1 radiculopathy
The H-reflex is an evoked potential study performed by submaximal electrical stimulation of the S1 root and measuring the nerve conduction velocity proximally.
Its absence indicates proximal (root) injury.
It is the electrodiagnostic equivalent of the ankle jerk.
The H-reflex may demonstrate abnormalities within 1 or 2 days after nerve root injury.
Preston DC, Shapiro BE: Electromyography and neuromuscular disorders, 2nd ed. Boston: Butterworth-Heinemann, 2005.