late response
Delayed muscle responses following nerve stimulation, including H-reflexes and F-waves.
Full Definition
Late responses are delayed electromyographic responses that occur after the direct muscle response (M-wave) following peripheral nerve stimulation. The two main types are H-reflexes and F-waves. H-reflexes represent monosynaptic spinal reflexes and are routinely tested in the soleus muscle via tibial nerve stimulation. F-waves result from antidromic activation of motor neurons and provide information about proximal nerve segments and anterior horn cell function. Late responses are valuable for detecting proximal neuropathies, radiculopathies, and conditions affecting the proximal nerve segments that may not be apparent on routine nerve conduction studies.
Usage
Usage note: Specify whether referring to H-reflex or F-wave when documenting findings.
In Context
- "Late responses showed prolonged F-wave latencies suggesting proximal median nerve involvement." — Nerve conduction study report
- "The H-reflex was absent bilaterally, consistent with S1 radiculopathy." — Electrodiagnostic findings