Relaxing Effect of Acupuncture Stimulation on Hypertonic Muscle in a Rat Model

Background: The relaxing phenomenon induced by acupuncture on hypertonic muscle has not clearly been demonstrated. We studied whether acupuncture stimulation on the hypertonic muscle model induce relaxation. Methods: A rat model of hypertonia was created by inducing tetanic contraction in the triceps surae muscles of 21 Wistar rats (male, 12 weeks) with four electrical stimulations (80 Hz, 5 mA, 5 min.), with a 2 min. interval between each stimulation. The rats were randomly divided into two test groups: 1. Untreated group (N = 12), 2. Group treated with acupuncture stimulation of the triceps surae muscle (N = 9). Rats in the untreated group received no therapeutic treatment after the model was created. Acupuncture was performed within 5 min. after the model was created. Evaluations were taken before and 5 min., 1, 2 and 3 days after tetanic contraction was induced. The rats were anaesthetized and a tension sensor for measuring static and dynamic muscle tension was used to determine triceps surae muscle stretching tension during passive dorsal flexion of the foot (30°, 40°, 50°). Results: In both groups, at each of the angles of passive dorsal flexion, there was a significant increase in stretching tension 5 min. after inducing tetanic contraction compared to before induction, and statistics showed recovery to pre-induced tetanic contraction values after 1 day and thereafter. Compared to the untreated group, however, values 5 min. after induced tetanic contraction tended to be lower in the group treated with acupuncture stimulation. Conclusions: Compared to the untreated group, stretching tension values 5 min. after inducing tetanic contraction tended to be lower in the acupuncture group. This could be due to acupuncture stimulation causing changes in blood flow in the lower leg, including muscle tissue, resulting in reuptake of calcium by the sarcoplasmic reticulum, and/or the influence acupuncture on reducing lower leg edema. Acupuncture stimulation could also have an action on the γ fibers and Ib fibers associated with continuous muscle tonus and muscle relaxation.