Meridian-like character of reflex electromyogram activity in longissimus dorsi muscles

We studied the temporal and spacial character of the electromyogram (EMG) evoked by acupuncture in longissimus dorsi (LD) muscles of rat, and evaluated the effect of needling direction or local blockade on EMG propagation. When certain sites on LD muscle were acupunctured, asynchronous EMG could be activated not only at the acupunctured point, but also within the muscle region supplied by the adjacent 2–3 vertebral segments. The EMG evoked by stimulation on the borderline of aponeurosis and muscle venter was larger in amplitude than those on the other sites in the same vertebral segment. When the distance from the recorded site to stimulated site increased, the EMG amplitude decreased, and its latency prolonged. Acupuncture in an oblique direction toward rostral or caudal side of the muscle enhanced the EMG amplitude in the same direction. EMG activity was weakened and its propagation was blocked by local injection of procaine. These results indicated that the character of EMG propagation evoked by acupuncture was related to the mechanism of needle-feeling propagation along the meridian.