Ann Rehabil Med.  2014 Aug;38(4):494-505. 10.5535/arm.2014.38.4.494.

Evaluating the Differential Electrophysiological Effects of the Focal Vibrator on the Tendon and Muscle Belly in Healthy People

• Lee G
• Cho Y
• Beom J
• Chun C
• Kim CH
• Oh BM

• KMID: 2165732
• DOI: http://doi.org/10.5535/arm.2014.38.4.494

Abstract

OBJECTIVE
To investigate the electrophysiological effects of focal vibration on the tendon and muscle belly in healthy people.
METHODS
The miniaturized focal vibrator consisted of an unbalanced mass rotating offset and wireless controller. The parameters of vibratory stimulation were adjusted on a flat rigid surface as 65 microm at 70 Hz. Two consecutive tests on the different vibration sites were conducted in 10 healthy volunteers (test 1, the Achilles tendon; test 2, the muscle belly on the medial head of the gastrocnemius). The Hoffman (H)-reflex was measured 7 times during each test. The minimal H-reflex latency, maximal amplitude of H-reflex (Hmax), and maximal amplitude of the M-response (Mmax) were acquired. The ratio of Hmax and Mmax (HMR) and the vibratory inhibition index (VII: the ratio of the Hmax after vibration and Hmax before vibration) were calculated. The changes in parameters according to the time and site of stimulation were analyzed using the generalized estimating equation methods.
RESULTS
All subjects completed the two tests without serious adverse effects. The minimal H-reflex latency did not show significant changes over time (Wald test: chi2=11.62, p=0.07), and between the two sites (chi2=0.42, p=0.52). The changes in Hmax (chi2=53.74, p<0.01), HMR (chi2=20.49, p<0.01), and VII (chi2=13.16, p=0.02) were significant over time with the adjustment of sites. These parameters were reduced at all time points compared to the baseline, but the decrements reverted instantly after the cessation of stimulation. When adjusted over time, a 1.99-mV decrease in the Hmax (chi2=4.02, p=0.04) and a 9.02% decrease in the VII (chi2=4.54, p=0.03) were observed when the muscle belly was vibrated compared to the tendon.
CONCLUSION
The differential electrophysiological effects of focal vibration were verified. The muscle belly may be the more effective site for reducing the H-reflex compared to the tendon. This study provides the neurophysiological basis for a selective and safe rehabilitation program for spasticity management with focal vibration.

Keyword

Vibration; Electrophysiology; Monosynaptic reflex; H-reflex; Muscle spasticity

MeSH Terms

Achilles Tendon
Electrophysiology
H-Reflex
Head
Healthy Volunteers
Muscle Spasticity
Reflex, Monosynaptic
Rehabilitation
Tendons*
Vibration

Figure

• 

  Fig. 1 Structure of the focal vibrator. The custom-made vibrator that consists of a flat DC micromotor with an integrated encoder and an offset unbalanced mass rotating about the motor shaft.

• 

  Fig. 2 Application of the focal vibrator and the location of the electrodes. The location of the electrodes and focal vibrator are illustrated (A). The focal vibrator is shown on the insertion site of the Achilles tendon (B) and on the muscle belly of the medial head of the gastrocnemius (C).

• 

  Fig. 3 Experiment design of the two consecutive tests. Test 1 was the experiment of the tendon vibration and test 2 was the experiment of the muscle belly (medial head of the gastrocnemius muscle). Each test consisted of 20 minutes of vibratory stimulation and 5 minutes of non-vibration. In each test, 7 consecutive Hoffman (H)-reflex measurements were performed: pre-vibration (T0), 5 minutes after vibration started (T1), 10 minutes after vibration started (T2), 15 minutes after vibration started (T3), 20 minutes after vibration started (T4), 1 minute after cessation of vibration (T5), and 5 minutes after cessation of vibration (T6). Between the vibratory stimulation and non-vibration, resting periods of 10 minutes were included to prevent post-activation depression of the H-reflex.

• 

  Fig. 4 Changes in the Hmax/Mmax ratio (HMR). During vibratory stimulation, decrements in the HMR were observed. After the cessation of vibration, the decrements were reduced instantly. The changes in HMR were larger in the muscle belly stimulation test (test 2) than in the tendon vibration test (test 1).

• 

  Fig. 5 Changes in the vibratory inhibition index. The pattern of changes was similar to that of the Hmax/Mmax ratio.

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