Needle EMG · Beginner

The four phases of needle EMG

Insertion, rest, activation, recruitment

Structure the examination around insertion, rest, slight contraction and increasing effort.

3 learning sectionsCompiled 2026-09-08English edition · Traditional Chinese available

01Insertion and rest

  • Insertional activity is a brief response to needle movement. Once movement stops, assess for persistent spontaneous activity.
  • With adequate relaxation and away from the endplate zone, identify fibrillations, positive sharp waves, fasciculations and other discharges.

02Slight contraction

  • Assess MUAP duration, amplitude, phases and stability.
  • Needle position, muscle, age and effort affect morphology. Sample multiple sites.

03Increasing effort

  • Compare the number of units and firing rates with the force produced.
  • Pain, limited understanding and upper motor neuron dysfunction may reduce activation; distinguish this from reduced recruitment.

Pause and explain

Explain in your own words: “Interpret morphology together with recruitment and the distribution of affected muscles.” Then think of a situation in which it could be misinterpreted.

Show a review prompt

One polyphasic MUAP cannot diagnose radiculopathy or myopathy.

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References and further reading

Educational synthesis; independent neuromuscular specialist review is pending. Publication dates and compilation dates are distinct. This is an original teaching synthesis; consult the source for complete methods and criteria.