Updated: Dec 21, 2022
Clinicians place active electrodes over the target muscle belly (i.e., central region) to record its full voltage. A stronger EMG signal enables an electromyograph to record muscle electrical activity more accurately. Explain muscle palpation and obtain written consent. With a staff member present, palpate the muscle with a gloved hand as it contracts and relaxes to find the muscle belly. Draw circles with a grease pencil to guide sensor placement. Space 0.5-cm active electrodes about 1.5 cm apart. Place the reference electrode within 15 cm of either active. Reference positioning is less critical than active placement.
In the graphic adapted from MYOWARE, compare the signal voltage from the belly with signals from distant sites. Electrodes placed near a muscle's insertion into a tendon or offset to the side reduce EMG signal strength. Likewise, placement over the wrong muscle or at an angle from the muscle belly results in misleading measurements (Sherman, 2002).
Thought Technology Ltd. generously provided the diagrams below from their Basics of Surface Electromyography Applied to Physical Rehabilitation and Biomechanics (2009).
EMG Sensor Color Codes
Note that the color code for active electrodes varies with the manufacturer. For Thought Technology Ltd., the active electrodes are blue and yellow.
For MindMedia, the active electrodes are white and red.
Clinicians should place active EMG sensors over the muscle belly to record a muscle's full voltage. Explain the muscle palpation procedure, obtain written consent, and identify the muscle belly with staff supervision. The color convention for active and reference electrodes varies across manufacturers.
active electrode: the electrode placed over the belly of a target muscle.
electromyography (EMG): an instrument that measures the muscle action potentials that initiate skeletal muscle contraction
muscle belly: a muscle's central region.
muscle electrical activity: the muscle action potentials that trigger skeletal muscle contraction; EMG voltage.
palpation: a procedure in which a client contracts and relaxes a muscle while a clinician locates the muscle belly by touch.
reference electrode: an electrode placed within 15 cm of either active electrode.
Florimond, V. (2009). Basics of surface electromyography applied to physical rehabilitation and biomechanics. Thought Technology Ltd.
Peek, C. J. (2016). A primer of traditional biofeedback instrumentation. In M. S. Schwartz, & F. Andrasik (Eds.). Biofeedback: A practitioner's guide (4th ed.). The Guilford Press.
Peper, E., Gibney, K. H., Tylova, H., Harvey, R., & Combatalade, D. (2008). Biofeedback mastery: An experiential teaching and self-training manual. Association for Applied Psychophysiology and Biofeedback.
Sherman, R. (2002). Hooray! The revolution is here! (But don't stop it in its tracks). Biofeedback, 30(1), 7, 18.
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