A noninvasive test for estimating myosin heavy chain of the vastus lateralis in females with mechanomyography

Influence of Pennation Angle and Muscle Thickness on Mechanomyographic Amplitude–Torque Relationships and Sex-Related Differences in the Vastus Lateralis

“…Indeed, once motor units fuse, they are no longer capable of contributing to the amplitude of the MMG signal despite being active [ 69 ]. In support, individuals expressing greater type I percent myosin heavy chain expression have exhibited lower MMG RMS values during isometric [ 23 , 24 , 25 , 26 ] and dynamic knee extensor testing [ 70 ]. Although we did not collect muscle biopsies, the greater mechanical behavior displayed by the males during the linearly increasing segment ( b terms) and at steady torque (MMG RMS ) likely suggests percent myosin heavy chain expression differences between the sexes.…”

“…The signals were bandpass-filtered (fourth-order Butterworth) at 5–100 Hz. For the submaximal muscle action, the torque and MMG signals were analyzed with consecutive, non-overlapping 0.25 s epochs [ 25 , 26 , 27 , 34 , 35 ]. The amplitude of the MMG signal was calculated with root mean square (RMS).…”

“…For the linearly increasing segment of the targeted torque template, the torque and MMG RMS values for each quarter-second epoch underwent a natural log transformation, and simple linear regression models were applied [ 25 , 26 , 27 , 34 , 35 ]. The equations were represented as: ln[ Y ] = b (ln[ X ]) + ln[ a ] where ln[ Y ] represents the natural log of the MMG RMS values, ln[ X ] represents the natural log of the torque values, b represents the slope, and ln[ a ] = the natural log of the y -intercept.…”

“…After the antilog transformation, this can also be expressed as an exponential equation: Y = aX b where Y = the predicted MMG RMS values, X represents torque, b represents the slope of Equation (1), and a represents the antilog of the y-intercept from Equation (1). For the 12 s steady torque segment, MMG RMS was calculated by averaging the values during the entire 12 s targeted contraction torque [ 25 , 26 , 34 , 35 ]. The b terms were calculated with Microsoft Excel ® version 16.…”

“…However, it appears that MMG RMS can also be influenced by the physical properties of the motor unit pool. For example, greater b terms (slopes) calculated from the log-transformed MMG RMS –force/torque relationships during linearly increasing and decreasing muscle actions, and MMG RMS values at steady force/torque, have been reported for individuals expressing greater amounts of type II percent myosin heavy chain isoform content [ 23 , 24 , 25 , 26 ]. In addition, MMG RMS –torque relationships can also be influenced by muscle architecture [ 27 ].…”