: Voluntary Muscle Activity Pattern by Electromyography

: What This Test Measures

: Electromyography (EMG) records the electrical signals that muscle fibers generate when they are activated. During the voluntary activity portion, you are asked to gently and then firmly tighten the muscle while the needle electrode picks up the resulting electrical pattern. The physician looks at how the signals begin, how dense they become with effort, and how they look when you relax.

: How the Procedure Is Done

: A small needle electrode is placed into the chosen muscle through the skin. You may feel a brief pinch when the needle is inserted and some discomfort when you contract the muscle. The physician asks you to relax, then to tighten the muscle gradually and with more force, and records the electrical pattern at each level of effort. Several muscles may be tested depending on your symptoms.

: What the Pattern Can Show

: The voluntary activation pattern can appear normal, reduced, or altered in shape and size. These patterns help the physician judge whether muscle fibers are functioning normally, whether nerve connections to the muscle are impaired, or whether the muscle itself is affected. The pattern is interpreted together with the rest of the EMG study and your clinical history.

: How to Prepare and What to Expect

: Your care team will give you specific instructions, which may include avoiding lotions on the skin and informing them of blood-thinning medicines or bleeding problems. The test usually takes place in a clinic or nerve-conduction laboratory and lasts from minutes to longer depending on how many muscles are studied. Mild soreness or small bruises at the needle sites can occur and typically resolve quickly.