Inhibitory Effect of Acupuncture on Vibration-Induced Finger Flexion Reflex in Humans: Comparisons Among Radial, Median, and Ulnar Nerve Stimulation

Abstract

Background: Vibration-induced finger flexion reflex (VFR) is inhibited with acupuncture to TE 5 or LI 4 at the skin innervated by the radial nerve.

Objective: The aim of this study was to determine if acupoints in regions innervated by the radial nerve are specific to inhibit VFR.

Materials and methods: This experiment was performed using a crossover design with 3 acupuncture groups (needle insertion to the right LU 11, PC 9, or SI 1) and a control group (no needle treatment). Each acupoint was randomly needled on separate days. Ten healthy volunteers were recruited for this study. VFR was induced by applying vibration on the volar side of the right middle fingertip. An acupuncture needle was inserted in the acupoint and retained for 5 minutes. For the main outcome measure, maximum finger flexion force (MFFF) was measured during vibration and was compared among four groups.

Results: MFFFs in the acupuncture groups were significantly lower (p<0.05) than that in the control group. However, no significant difference was observed in MFFFs in the three intervention groups after acupuncture to LU 11, PC 9, and SI 1.

Conclusions: Acupuncture to the right LU 11, PC 9, or SI 1 point inhibited the ipsilateral VFR, which suggests that afferent inputs from the radial nerve with needle insertion were not specific, compared with those from the median and ulnar nerves to suppress neuronal activities in the VFR reflex circuits.

Keywords: Acupuncture; Flexion Reflex; Median Nerve; Radial Nerve; Stiff Muscles; Ulnar Nerve; Vibration.

FIG. 1.

Schema for experimental settings. Vibration at 60 Hz was applied to the volar side of the middle fingertip. Flexion force was measured by a pen recorder through a force transducer.

FIG. 2.

Acupoint locations in the right hand: LU 11; PC 9; and SI 1.

FIG. 3.

Records of finger flexion forces induced by vibration-induced finger flexion reflex (VFR) in a typical subject before (left column) and after (right column) acupuncture. The subjects in the control group (upper) had no obvious change in VFR caused by adaptation or fatigue in the finger flexion muscles. Finger flexion force during VFR decreased after acupuncture (second, third, and fourth row from the top), compared with those before acupuncture. sec, seconds.

FIG. 4.

Changes in maximum finger flexion force (MFFF) for 10 subjects in the acupuncture group (the left box, LU 11; the second box from the left, PC 9; and the third box from the left, SI 1) and control group (the right box in each timepoint). Vertical axis is the percentage of 10 minutes (min) before value of MFFF and the horizontal axis is time. The top, middle, and bottom lines of the boxes correspond to the 75th, 50th (median), and 25th percentiles, respectively. The whiskers extend from the minimum to the maximum value. The circles indicate the arithmetic mean. The broken line represents baseline (10 min before value of MFFF). *p<0.05, **p<0.01.