Effect of muscular ultrasound stimulation on power spectrum electromyography during a strengthening training

The purpose of this study is to describe the electromyographic (EMG) power spectral evolution during a muscle strengthening training based on ultrasound stimulation applied to the right rectus femoris muscle simultaneously with its maximum voluntary isometric contraction (MVIC) in ten healthy subjects. From the surface EMG of rectus femoris the Zero Crossing (ZC) and integrated EMG (IEMG) were calculated. The Mean Power Frequency (MPF) and Median Frequency (MF) from the EMG power spectrum were obtained using a maximum entropy method. An Analysis of Variance (ANOVA) for repeated measures showed significant changes for IEMG and ZC throughout sessions and for MPF, MF and ZC between the pretest and posttest. Immediate increases in MPF, MF and ZC were observed (paired t-test, p < 0.05) after training and an increment of IEMG during sessions (one-way ANOVA, p = 0.01). The ultrasound pulsed stimulation applied simultaneously with a MVIC produced the development of the muscle force. The mechanism of action of this application could be the mechanical effect, compression and rarefaction, produced by the ultrasound stimulation during the muscle contraction process.