In spite of being a useful method on muscle contraction analysis, few studies have been dedicated to understand how some anthropometrical parameters can interfere in the mechanomyographic (MMG) signal properties. Therefore, the aim of this study was to evaluate the effects of skinfold thickness and arm circumference in the MMG signal behavior in the temporal and frequency domains at different levels of isometric contraction. Twenty-one males (24.9 ± 7.8 years) and 21 females (20.7 ± 2.5 years), all right-handed, participated in this study. Prior to the MMG signals collection, a maximum voluntary contraction test (MVC) was performed to further determine the five levels (20%, 40%, 60%, 80% and 100% of CVM) used during the tests. The two groups performed isometric contractions in the five different levels while MMG signal was collected from the right biceps brachii muscle by a biaxial accelerometer. The root mean square value (RMS), and the median frequency (MF) calculated from the MMG power spectrum were extracted from the MMG signals in X direction, which meant perpendicular to the muscle fibres direction. The bicipital skinfold thickness (BD_DC_B), and the circumference of the right arm, with and without contraction of elbow muscles flexors, have also been measured. The MF presented a decreasing behaviour with the increasing level of contraction; the RMS value followed an increasing pattern, though. There were significant statistical differences (p < 0.05) for the anthropometric variables between groups. It is suggested that the RMS value, differently from the MF, which can be disrupted by the tissues between the muscle and the transducer, should be better correlated with muscle force level.
mechanomyography; MMG; MMG signal; vibromyography; VMG
