Mechanomyographic responses during voluntary ramp contractions of the human first dorsal interosseous muscle

Abstract

The aim of this study was to examine the mechanomyogram (MMG) and force relationship of the first dorsal interosseous (FDI) muscle as well as the biceps brachii (BB) muscle during voluntary isometric ramp contractions, and to elucidate the MMG responses resulting from the intrinsic motor unit (MU) activation strategy of FDI muscle with reference to the MMG of BB muscle. The subjects were asked to exert ramp contractions of FDI and BB muscle from 5% to 70% of the maximal voluntary contraction (MVC) at a constant rate of 10% MVC/s. In FDI muscle, the root-mean-squared amplitude (RMS) of the MMG decreased slowly with force up to 21%, and then a progressive increase was followed by a relatively rapid decrease beyond 41% MVC. The RMS/%MVC relationship in BB muscle consisted of an initial slow increase followed by a rapid increase from 23% MVC and a progressive decrease beyond 61% MVC. With respect to the mean power frequency (MPF), FDI muscle demonstrated no obvious inflection point in the MPF/%MVC relationship compared with that in BB muscle. Namely, the MPF of FDI muscle increased linearly through the force levels exerted. In contrast to FDI muscle, the MPF/%MVC relationship in BB muscle was decomposed into four specific regions: (1) a relative rapidly increase (<34% MVC), (2) a slow increment (34-53% MVC), (3) a temporary reduction (53-62% MVC), and (4) a further rapid increase (>62% MVC). The different MMG responses between FDI and BB muscles are considered to reflect the fact that the MU activation strategy varies among different muscles in relation to their morphology and histochemical type. Namely, the rate coding of the MUs plays a more prominent role in force production in relatively small FDI muscle than does MU recruitment compared with their respective roles in the relatively large BB muscle.

Influence of subcutaneous fat on mechanomyographic signals at three levels of voluntary effort

“…The facts presented can be attributed to the increase in mechanical activity resulting from the sum of the action potentials (APs) of the MUs with the increase of muscular force (Yoshitake et al, 2002) even in lower magnitudes (Akataki et al, 2003). This process occurs because of the redistribution of aqueous material present in the sarcoplasm (Neering et al, 1991), and because the mechanical signals generated from this process travel through the material between the muscle and the sensor (Dalton and Stokes, 1993).…”

“…The use of MMG as indicator of the level of MUs firing rates, as well as indicator of increase of the action potentials (APs) originated from the skeletal muscle (Akataki et al, 2003), may be subject to attenuation in acquisition caused by thicker layers of subcutaneous fat. Therefore, it is important to consider the effects of fat when adopting MMG as a tool in applications such as prostheses control (Orizio et al, 2003), monitoring of muscular fatigue (Orizio et al, 2003;Scheeren et al, 2010;Tarata, 2003), neuromuscular diseases diagnosis (Hu et al, 2007), respiratory muscle work (Sarlabous et al, 2014), among others.…”

Gender Comparisons of Mechanomyographic Amplitude and Mean Power Frequency versus Isometric Torque Relationships

“…For the biceps brachii, several recent studies have reported increases in both MMG amplitude and MMG mean power frequency with submaximal isometric torque (Akataki, Mita, Watakabe, & Itoh, 2001;Akataki et al, 2003;Beck et al, 2004;Orizio et al, 1989;. At torque levels ≥ 60-80% MVC, however, MMG amplitude for the biceps brachii plateaus or decreases (Akataki et al, 2001;Beck et al, 2004;Orizio et al, 1989;.…”

“…During voluntary contractions, the asynchronous motor unit activities are summated to form the surface MMG, and it has been suggested that the time and frequency domains of the MMG signal may provide information regarding the unique motor unit activation strategies (motor unit recruitment and firing rate) that modulate isometric torque production in various muscles (Akataki, Mita, Watakabe, & Itoh, 2003;Orizio, 1993;Orizio et al, 2003;Orizio, Liberati, Locatelli, De Grandis, & Veicsteinas, 1996;Orizio, Perini, Diemont, Figini, & Veicsteinas, 1990;Orizio, Perini, & Veicsteinas, 1989). Specifically, it has been shown that MMG amplitude is related to motor unit recruitment, while the frequency domain of the MMG signal may contain information about motor unit firing rate (Akataki et al, 2003;Orizio, 1993;Orizio et al, 2003;Orizio, Solomonow, Baratta, & Veicsteinas, 1993).…”

“…Specifically, it has been shown that MMG amplitude is related to motor unit recruitment, while the frequency domain of the MMG signal may contain information about motor unit firing rate (Akataki et al, 2003;Orizio, 1993;Orizio et al, 2003;Orizio, Solomonow, Baratta, & Veicsteinas, 1993).…”