Effect of whole-body vibration on motor neuron excitability in healthy young men

Background Whole-body vibration (WBV) has been increasingly used for performance enhancement as well as for treatment of some conditions. There is much focus on the study of muscular performance accompanied by WBVs; however, little is known about its effect on motor units – whether it has excitatory or inhibitory effects. The purpose of this study was to investigate the effect of a single bout of WBV on motor neuron excitability in healthy individuals immediately and 30min after application. Participants and methods Sixty healthy men participated in this study; their ages ranged between 18 and 25 years. They were randomly divided into two equal groups – the study group and the control group – each containing 30 men who were selected by drawing ballots from sealed envelopes. The experimental group received WBV with a frequency of 50–60Hz and amplitude of 0–10mm for 1min, with a 1min rest period between each vibration set, which was repeated five times. The control group stood on the WBV device for the same duration while it was off. Hoffman reflex amplitude and H/ M ratio were measured from the soleus muscle (posterior tibial nerve) before and 0 and 30min after application in both groups using surface electromyography. Results There was significant decrease in Hoffman reflex amplitude at 0 and 30min in the study group compared with the control group ( P =0.002 and 0.01, respectively). Moreover, there was significant decrease in H/M ratio at 0 and 30min in the study group compared with the control group ( P =0.0001 and 0.03, respectively). Conclusion WBV decreases motor neuron excitability and thus may have therapeutic implications for people with central nervous system disorders, in whom spasticity is a major manifestation.