Syncronicity relationship between the mechanomyography peak energy frequency and the maximum electrically evoked contraction in paraplegics

The goal of this paper is to investigate the temporal-spectral decomposition content during a maximal electrically evoked contraction (MEEC) in two spinal cord injured participants using triaxial mechanomyography (MMG). Two male spinal cord injured volunteers performed the tests both injured at T7 neurologic level. The triaxial MMG signal of rectus femoris muscle was processed with Cauchy wavelet transform adjusted to third-order 5-50 Hz bandpass Butterworth filter. A custom electrical stimulator voltage-controlled was configured: pulse frequency set to 1 kHz (20% duty cycle) and burst (modulating) frequency set to 70 Hz (20% active period). The MEEC force was performed by increasing the electrical stimulating magnitude (~3 V/s to avoid motoneuron adaptation/habituation) until the force started to level off. We conclude that the peak energy of MMG signal frequency did not occur simultaneously with the maximal electrically evoked contraction to rectus femoris muscle. Moreover, the vibration vector of muscle, expressed in three axes (X, Y and Z), presented different fired frequencies, mainly between X (transverse) and Z (perpendicular) axis, where the frequencies fired by Z axis were greater.