Background and aim: Since 1998, the effect of traction on the H- reflex has been investigated by Hiraoka and the other researchers. Some of them have been done on lower extremity and the other on the upper extremity. The effect of traction was assessed by H reflex amplitude. Different results have been achieved. The new method which has been used since 2000, the effect of cervical traction on the H reflex was carried out by measuring H reflex slope .In this experiment the effect of manual cervical traction has been studied on the H slope of the upper extremity. Now we have sought to extend this work by examining the effects of cervical traction with 3 kg force on the H slope of the lower extremity 

Materials and Methods: This study was administered to sixteen healthy men with a mean age 23.12 of years and SD=2.55. The parameters of H reflex were recorded before and after of cervical traction .All data were analyzed with SPSS (V: 11.5).    

Results: The results showed that, there were no significant differences between before and after the application of cervical traction in H reflex parameters, ratio of H max/M max amplitude and M slope. But H slope and ratio of H slope /M slope were increased significantly after the application of traction (P<0.001).

Conclusion: The present study showed that traction with 3 Kg force can increase motor neuron excitability of soleus muscle and this result is against the previous study. This could be due to the application of the new method (H slope), which is more precise.

Background and Aim: Despite the widespread use of whole body vibration (WBV),especiallyin recent years, its neurophysiological mechanism is still unclear and the results about the facilitatory or inhibitory effects of WBV widely vary in different studies. The aim of this study was to compare between immediate (one session) and short term (12 sessions) effects of WBV on the spinal motor neurons excitability in healthy young men.

Materials and Methods: Ten voluntary non-athlete healthy young-men (mean age:26.1±2.23) were participated in this study.In the sham sessions subjects stood on the turned off vibration plate while were maintaining the semi-squat position and then after 2 weeks wash-out, vibration training sessions were done on the same position with frequency of 30 HZ and peak to peak amplitude of 3 mm training sessions (sham & vibration) consisted of 12 sessions (3 sessions per week) and 4 set in each of them, weekly one set added to the training protocol. H reflex recruitment curve of soleus muscle was recorded before and after first and also 12th sessions in both sham and vibration training protocol. Ascending slope of recruitment curve, threshold and peak amplitudes and related intensities, amplitude of Mh and Hmax/Mmax ratio were determined.

Results: Immediate effects of vibration training 12th session caused a significant decrease of threshold amplitude and an increase of peak intensity (p=0.05 and p=0.05 respectively). Short term WBV training significantly decreased the threshold intensity of soleus recruitment curve (p=0.01).

Conclusion: The results suggest the inhibitory effect of acute WBV training on the spinal motor neurons excitability. It seems that short term WBV training may be effective to facilitate the motor neurons excitability or increase the muscle spindle sensitivity.

Key Words: Whole body vibration, H reflex recruitment curve, Soleus muscle, Short term training