Which diagnostic test records the electrical activity of muscles during rest and contraction?

• A. EEG
• B. ECG
• C. Endoscopy
• D. EMG

Answer: (D)

Recording electrical activity from muscles as they are at rest and as they contract is what electromyography does. EMG uses tiny needles or surface sensors to pick up the electrical signals generated by muscle fibers. When a muscle is at rest, EMG can reveal abnormal spontaneous activity that points to nerve or muscle pathology. When the muscle is active, EMG analyzes how motor units are recruited and how their electrical signals behave, helping distinguish whether a problem lies in the nerve supplying the muscle or in the muscle itself. The other tests measure different things: EEG tracks brain electrical activity, ECG tracks heart electrical activity, and endoscopy is a visual examination of internal surfaces. Because EMG directly records muscle electrical activity during both states, it best fits the description.