A vibratory bar for upper body: feasibility and acute effects on EMGRMS activity

The purpose of this study was to determine the feasibility of a purpose-designed vibratory bar (VB) as a potential vibration training device and thereafter to assess its effects on upper-body muscles' electromyographic (EMG) activity during vibration. During session 1, 16 physically active males held the VB during the bench press exercise in an isometric extended position (EP) in the following vibration conditions selected in the inverter ([sub.i]): no vibration (0), 20, 30, 40, and 50 [Hz.sub.i]. Maximal acceleration ([Acc.sub.max]), frequency (Freq), and peak-to-peak amplitude ([Amp.sub.p-p]) obtained at the center (C) and at the end (E) of the VB were assessed using an accelerometer. During session 2, EMGrms of the triceps, deltoid, and pectoralis major were recorded in EP and isometric flexion position (FP) at 0, 25, and 45 [Hz.sub.i]. The [Acc.sub.max], Freq, and [Amp.sub.p-p] values ranged from 37.4 to 96.4 m x [s.sup.-2], 18.5 to 30.8 Hz, and 4.6 to 6.1 mm, respectively. The accelerometer's position had a significant effect on the [Acc.sub.max] and [Amp.sub.p-p]. All Freq obtained at C and E were different (p < 0.001) to the [Freq.sub.i]. An increase (p < 0.05) in EMGrms was observed in both vibration conditions compared with 0 [Hz.sub.i], except during 25[Hz.sub.i] for deltoid and pectoralis muscle in FP. Although no significant differences were found in any of the muscles between 45 [Hz.sub.i] and 25[Hz.sub.i], the highest EMGrms was elicited at 45[Hz.sub.i]. Although the registered VBs' parameters seem appropriate for vibration training, the frequency in the FP should be higher than 25 [Hz.sub.i] to induce significant increases in EMGrms in deltoid and pectoralis muscles. The use of a vibratory bar may be a suitable system to simultaneously stimulate upper-body muscles. KEY WORDS vibration exercise, neuromuscular, posture, strength, reflex