In normal muscle, there is a brief increase in electrical potentials lasting 300-500 ms in duration. Insertional activity deals with what hap pens immediately following insertion of the needle into the muscle and minimally advancing it with short, quick bursts. The first component is insertional activity. Insertional and Spontaneous ActivityĮvaluation of the muscle at rest can be divided into two additional categories. Needle EMG studies can be broken down into two basic components: 1) the muscle at rest and, 2) voluntary muscle contraction. This means that only a small portion of the muscle is actually evaluated during the needle EMG portion of the test. While the muscle fibers belonging to a single motor unit can be distributed over 5-10 mm or more, the needle records activated motor units up to only about 1-2 mm from the recording tip. The needle EMG examination is performed “on the fly” requiring in-depth knowledge of nerve and muscle physiology and how they relate to both normal and abnormal electrical activity in the muscle. In Part Two, I will cover principles of needle electromyography ( EMG ), specific diseases and injuries that relate to hand therapy, and how EMG/NCS findings relate to outcomes for certain injuries and surgeries of the upper extremities. In Part One of this article, I discussed the basics of nerve conduction studies and waveform analysis.
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