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

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.

Ameliorated Effects of High Frequency Sinusoidal Vibration Given to Soleus Muscle on H Reflex in Rats Under Tail Suspension / 航天医学与医学工程

Objective To observe the changes in excitability of alpha-motoneuron responding to the muscle spindles afferent excitability in the model rats and explore whether the changes in this excitability to be changed as high frequency sinusoidal vibration acted on the soleus muscle.Methods The simulated weightlessness model was created by the tail-suspension.Mechanical vibrations at a frequency of 100 Hz with amplitude of 0.3 mm were acted on soleus muscle.The electromyogram of soleus muscle evoked by electrical stimulation of the sciatic nerve was recorded in control rats and HS rats.Results It was showed that HS and HFV did not influence the tendency of changes in amplitude of H reflex when the stimulation intensity increased.However,after 14-day HS,mean maximal motor response(Mmax)and mean maximal monosynaptic reflex/Mmax(Hmax/Mmax)both significantly decreased,respectively(P0.05).Conclusion It is suggested that HS should lead to the decrease in motoneurons excitability which is resulted from the reduction of muscle spindle afferent.HFV acted on soleus muscle of rats can improve the excitability of alpha-motoneurons in spinal cord during hindlimb suspension.