Mechanomyogram and force relationship during voluntary isometric ramp contractions of the biceps brachii muscle

Abstract

The aim of the present study was to examine the non-stationary mechanomyogram (MMG) during voluntary isometric ramp contractions of the biceps brachii muscles using the short-time Fourier transform, and to obtain more detailed information on the motor unit (MU) activation strategy underlying in the continuous MMG/force relationship. The subjects were asked to exert ramp contractions from 5% to 80% of the maximal voluntary contraction (MVC) at a constant rate of 10% MVC/s. The root mean squared (RMS) amplitude of the MMG began to increase slowly at low levels of force, then there was a slight reduction between 12% and 20% MVC. After that, a progressive increase was followed by a decrease beyond 60% MVC. As to the mean power frequency (MPF), a relatively rapid increase up to 30% MVC was followed by a period of slow increment between 30% and 50% MVC. Then temporary reduction at around 50% MVC and a further rapid increase above 60% MVC was observed. The interaction between amplitude and MPF of the MMG in relation to the MU activation strategy is discussed for five force regions defined on the basis of their inflection points in the RMS-amplitude/force and MPF/force relationships. It was found that the MMG during ramp contractions enables deeper insights into the MU activation strategy than those determined during traditional separate contractions. In addition, this contraction protocol is useful not only to ensure higher force resolution in the MMG/force relationship, but also to markedly shorten the time taken for data acquisition and to reduce the risk of fatigue.

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

“…The amplitude of the MMG signal is determined by the number of active motor units and their firing rates (Orizio, 1993;Orizio et al, 2003), and although not directly verified (Akataki et al, 2003), it has been suggested that the MMG frequency content qualitatively reflects the global firing rate of the unfused activated motor units (Akataki et al, 2001;Bichler, 2000;Bichler & Celichowski, 2001;Orizio, 1993;Orizio et al, 2003). Thus, examination of the MMG amplitude and mean power frequency vs. isometric torque relationships may provide information regarding the unique motor unit activation strategies (recruitment and firing rate) …”

“…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;.…”

“…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;. Although the exact mechanisms are unclear, it has been hypothesized that a plateau or decrease in MMG amplitude at high levels of isometric torque may be due to muscle stiffness and intramuscular fluid pressure and/or fusion of motor unit twitches at high firing rates (Akataki et al, 2001;Beck et al, 2004;Orizio et al, 1989;.…”

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

“…Isometric contraction was employed to measure the force (Neering et al, 1991;Akataki et al, 1996;Akataki et al, 2001;Alves and Chau, 2008;Krueger et al, 2013).…”

“…MMG is used in many applications, including: prostheses control (Orizio et al, 2003); indication of muscle activation degree (Scheeren et al, 2010); monitoring of muscle fatigue (Orizio et al, 2003;Tarata, 2003); neuromuscular diseases diagnosis (Hu et al, 2007); obtainment of signals for the study of muscle strength gradation mechanisms (Akataki et al, 2001;Matta et al, 2005;Madeleine et al, 2001;Nogueira-Neto et al, 2013); evaluation of respiratory muscle work (Sarlabous et al, 2014); changes in MU activation strategies, which can occur with aging, neuromuscular diseases, endurance training programs, and care of injuries (Cooper et al, 2014); and Parkinson's disease (Marusiak et al, 2009;Malek and Coburn, 2012). In applications with comparisons between the MMG signal and the force response the biceps brachii (Orizio et al, 1989) and rectus femoris (Krueger et al, 2016;Shin et al, 2016) are the muscles more used due its easy accessibility and comparison capability.…”