EMG F-response

Introduction

An electromyograph (EMG) technique measuring the time required for a stimulus to propagate antidromically up an alpha motor neuron to the spinal cord & return orthodromically down the same axon.

Clinical significance

• F responses allow for an assessment of the entire nerve, including the proximal segment, which is not assessed by routine motor nerve-conduction studies
• semyelination is suggested if the time for an F response to appear is > 130% of the normal value
• in connection with the H-reflex, recognition of abnormal conduction velocity in peripheral neuropathy is 80-90%.
• conduction block in proximal nerve segments in inflammatory or demyelinating neuropathies may also be demonstrated

Additional terms

• electromyography (EMG)