The purpose of this study was to analyze if exposure to whole-body vibrations (WBV) of different frequencies with none or additional loads from 20 to 50 kg promotes changes in EMGrms activity of the quadriceps and gastrocnemious muscles. Sixteen male subjects with previous experience in strength training volunteered to participate. Subjects received the treatment while standing on a vibration platform with knees bent at 100º. Normalised EMGrms was recorded in vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF) and gastrocnemious medialis (GM) for 10 secs in the following twenty five conditions: no-vibration (NV), 30, 35, 40 and 50 Hz with body weight or with four different external loads (20, 30, 40 and 50 kg) over the shoulders. In all conditions, average normalised EMGrms from VM was significantly higher than in the NV condition. The same behaviour was observed in VL except in the 50 Hz with 20 kg condition. In RF only six conditions with 40 and 50 Hz were not significantly different compared with the NV condition. However, GM presented a different behaviour and only seven out of twenty four conditions were significantly different compared with the NV condition. The highest EMGrms was found at 30 Hz but no significant differences were found between the different frequencies employed. In all muscles except from GM and in all conditions with or without vibrations, a significant linear relationship was found between external load increments and EMGrms (%) signal increments These results suggest the use of EMGrms to monitor the optimal vibration frequency.