Effects of short-term training with WBV on the electromyography activity of the soleus and gastrocnemius muscles in healthy young women

Although the effects of whole body vibration (WBV) on the electromyographic (EMG) response of some muscles have been investigated in different studies، the effect of WBV on different types of motor units is not clear yet. The aim of the present study was to assess the different effects of a short-term WBV training on different motor units. Soleus (SOL) and gastrocnemius lateralis (GL) muscles were selected as the representatives of slow- and fast-twitch muscles، respectively. Twelve healthy young women (mean age 25. 66 ± 2. 71 years; mean height 161 ± 5. 6 cm; mean weight 66. 5 ± 5. 42 kg) were randomly allocated into the sham (n = 6) and WBV (n = 6) groups. The maximal isometric voluntary contraction (MIVC) of SOL and GL muscles was recorded before the initiation and after the termination of 12 training sessions. The training program was composed of the isometric squatting in both study groups such that in the sham group، the WBV machine set as off and in the WBV group، isometric squatting was offered in combination with whole body vibration (frequency of 30 Hz and peak to peak amplitude of 3 mm). The root mean square of EMG of soleous and gastrocnemius muscles was not statistically different between the two groups before training (P > 0. 05). The 12 sessions of training did not induce any statistically significant change in the muscle activity (EMGrms) of the SOL and GL muscles in either group (P > 0. 05). Although the RMS response of lateral gastrocnemius showed increasing behavior from the sham to the WBV groups، there was no significant difference in EMGrms values of these two groups (P > 0. 05). The difference value of EMGrms for soleus muscle did not also show any significant difference between these two groups (P > 0. 05). Despite the fact that EMGrms increases in soleus and gastrocnemius muscles were not statistically significant after WBV training، monitoring the response pattern in these two muscles between the sham and WBV groups is indicative of a positive effect of WBV on the lateral gastrocnemius motor units as a fast-twitch muscle.