Effect of reference electrode position on the compound muscle action potential (CMAP) onset latency

Gulapar Phongsamart, Jacqueline J. Wertsch, Mohammed Ferdjallah, John C. King, D. Terrence Foster

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Compound muscle action potential (CMAP) onset latency is interpreted to reflect the arrival time at the muscle of impulses in the fastest-conducting motor nerve fiber. However, we have observed that the position of the reference or indifferent electrode (E2) affects CMAP onset latency. Motor nerve conduction studies (NCS) of the median, ulnar, and deep ulnar motor (DUM) nerves on 20 normal hands were performed using both traditional bipolar and experimental monopolar (referenced to the contralateral hand) montages. As the position of E2 was altered, the CMAP onset latency varied 0.1-0.5 ms for the median NCS, 0.1-0.3 ms for the ulnar NCS, and 0.1-1.5 ms for the DUM NCS. This study demonstrates that E2 recorded potentials are significant and vary with positioning, affecting motor onset latency. This has implications both for reference values and the physiologic interpretation of the CMAP waveform.

Original languageEnglish (US)
Pages (from-to)816-821
Number of pages6
JournalMuscle and Nerve
Issue number6
StatePublished - 2002


  • CMAP latency
  • Median nerve
  • Nerve conduction studies
  • Reference electrode
  • Ulnar nerve

ASJC Scopus subject areas

  • Physiology
  • Clinical Neurology
  • Cellular and Molecular Neuroscience
  • Physiology (medical)


Dive into the research topics of 'Effect of reference electrode position on the compound muscle action potential (CMAP) onset latency'. Together they form a unique fingerprint.

Cite this