Relationships For Mechanomyographic Amplitude And Mean Power Frequency Vs. Torque During Isometric And Eccentric Isokinetic Muscle Actions

Abstract

PURPOSE To examine the mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus torque relationships during isometric and eccentric isokinetic muscle actions. METHODS Eight women (mean age/SD = 20.4/1.3 y) volunteered to perform isometric and eccentric isokinetic leg extension muscle actions at 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100% of maximal voluntary contraction (MVC) and peak torque (PT) on a Cybex 6000 dynamometer. An accelerometer (Entran, EGAS-FT-10- /V05) was placed on the vastus medialis to detect the MMG signal. The amplitude of the MMG signal was expressed as root mean square (rms), while frequency data were expressed as mean power frequency (MPF). Torque (Nm) was recorded by the dynamometer. RESULTS Polynomial regression analyses indicated that the relationship for MMG amplitude versus MVC was linear (r∧2 = 0.930) for the isometric muscle actions, but there was no significant relationship between MMG amplitude and PT for the eccentric isokinetic muscle actions. For the isometric and eccentric isokinetic muscle actions, the MMG MPF versus % MVC or % PT relationships were linear (r∧2 = 0.957 and 0.920, respectively). CONCLUSIONS The different torque-related responses for MMG amplitude and MPF may reflect differences in the motor control strategies that modulate torque production for isometric versus eccentric isokinetic muscle actions. These results suggested that isometric torque production was modulated by a combination of recruitment and firing rate, while eccentric isokinetic torque production was modulated primarily through firing rate.