Inter-individual variability among the mechanomyographic and electromyographic amplitude and mean power frequency responses during isometric ramp muscle actions

ArticleinElectromyography and clinical neurophysiology 47(3):161-73 · May 2007with6 Reads
Source: PubMed
Abstract
The purpose of this study was to examine the inter-individual variability in the patterns of responses for mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) of the vastus lateralis (VL) and rectusfemoris (RF) muscles during isometric ramp muscle actions of the leg extensors. Fifteen participants (mean +/- SD age = 24 +/- 4 years) performed two or three 6-s isometric ramp muscle actions with linear increases in torque from 15% to 90% of the highest maximal voluntary contraction (MVC) torque. Surface MMG and EMG signals were simultaneously recorded from the VL and RF muscles. The composite (averaged across subjects) and individual patterns of responses for the normalized MMG and EMG amplitude and MPF vs. isometric torque relationships were analyzed. The composite patterns for MMG amplitude for the VL and RF muscles were fit with cubic models, although, only 87% of the individual patterns (13 of 15 subjects) exhibited the same cubic pattern as the composite. For MMG MPF, the composite relationships were also cubic, but only 27% (4 subjects) and 40% (6 subjects) of the individuals exhibited the same patterns for the VL and RF respectively. 60% (8 subjects) of the individual EMG amplitude patterns of responses matched the same curvilinear composite patterns for the VL and RE, while only 7% (1 subject) and 27% (4 subjects) of the EMG MPF responses were similar to the composite models for the VL and RF muscles, respectively. Therefore, since the individual patterns did not always match the composite relationships (i.e., inter-individual variability), these findings suggested that the MMG and EMG amplitude and MPF vs. isometric torque relationships should be examined on a subject-by-subject and muscle-by-muscle basis during isometric ramp muscle actions.
    • "Barry and Cole (1990) and Orizio (1993) have suggested that these oscillations are manifested through (a) the gross lateral movement (GLM) of the muscle at the initiation of the contraction, (b) smaller subsequent lateral oscillations occurring at the resonant frequency of the muscle , and (c) dimensional changes in the active fibers. Numerous studies have utilized EMG and MMG simultaneously to examine motor unit control strategies during voluntary isometric ramp muscle actions (Akataki et al., 2004; Bilodeau et al., 1997; Cramer et al., 2004; Evetovich et al., 2003; Guo et al., 2010; Madeleine et al., 2001; Ryan et al., 2007). De Luca (de Luca et al., 1996) has suggested that the EMG amplitude-force relationship reflects the concurrent increases in motor unit recruitment and firing rates that regulate muscle force output, whereas, the MMG amplitude-force relationships have been able to distinguish between motor unit recruitment or rate coding as the primary mechanism to modulate force (Cooper, 2013). "
    [Show abstract] [Hide abstract] ABSTRACT: The purpose of this study was to examine possible correlations between skinfold thicknesses and the a terms from the log-transformed electromyographic (EMGRMS) and mechanomyographic amplitude (MMGRMS)-force relationships, EMG M-Waves, and MMG gross lateral movements (GLM). Forty healthy subjects performed a 6-s isometric ramp contraction from 5% to 85% of their maximal voluntary contraction with EMG and MMG sensors placed on the vastus lateralis (VL) and rectus femoris (RF). A single electrical stimulus was applied to the femoral nerve to record the EMG M-waves and MMG GLMs. Skinfold thickness was assessed at the site of each electrode. Pearson's product correlation coefficients were calculated comparing skinfold thicknesses with the a terms from the log-transformed EMGRMS-and MMGRMS-force relationships, EMG M-waves, and MMG GLMs. There were no significant cor1relations (p>0.05) between the a terms and skinfold thicknesses for the RF and VL from the EMGRMS and MMGRMS-force relationships. However, there were significant correlations (p<0.05) between skinfold thicknesses and the EMG M-waves and MMG GLMs for the RF (r=-0.521, -0.376) and VL (r=-0.479, -0.484). Relationships were only present between skinfold thickness and the amplitudes of the EMG and MMG signals during the non-voluntary muscle actions.
    Full-text · Article · Jan 2014
    • "fatiguing and MVCs (i.e., the basis for the ramp contraction) and the measurements were either concentric or isometric contractions that examined different muscle characteristics (metabolic versus activation strategies), the correlation does provide compelling evidence that the MMG RMS –force relationships may reflect muscle fiber type composition. Ryan et al (2007) examined the MMG RMS –torque relationships of the leg extensors (VL and RF) and observed clear differences in the patterns of response for MMG RMS at higher force levels. Differences in muscle fiber type composition have been attributed to the differences between the MMG RMS –force relationships reported between muscles. For example, Yo"
    [Show abstract] [Hide abstract] ABSTRACT: The purpose of the present study was to examine possible correlations between the b terms (slopes) form the log-transformed mechanomyographic amplitude (MMGRMS)-force relationships and the fatigue index calculated from 50 maximal concentric contractions. Forty healthy subjects (age = 21 ± 2 yr) performed isometric ramp contractions from 5% to 85% of their maximal voluntary contraction followed by a 50-repetition concentric fatigue protocol of the leg extensors, fatigue index (%) was calculated from the 50-repetitions. MMG was recorded during the ramp contractions from the vastus lateralis (VL) and rectus femoris (RF). The b terms (slopes) were calculated from the log-transformed MMGRMS-force relationships. Correlations were performed comparing the b terms from the MMGRMS-force relationships for the VL and RF with the fatigue index. Significant positive correlations were found among the b terms from the MMGRMS-force relationships for the VL (p = 0.007, r = 0.417) and RF (p = 0.014, r = 0.386) with the fatigue index. The b terms from the log-transformed MMGRMS-force relationships for the VL and RF may have reflected muscle fiber type composition and, thus, correlated with the fatigue index. This adds further support that the MMGRMS-force relationships may reflect muscle fiber type composition.
    Full-text · Article · Sep 2013
    • "Despite its broad applications, surface EMG is commonly used to examine motor control strategies, monitor muscle fatigue, assess neuromuscular alterations with aging, and track neurological diseases (De Luca 1984, Merletti et al 1990, Merletti et al 2002). The surface EMG–force relationships are usually characterized as linear or quadratic increases in EMG amplitude across the force (or torque) spectrum (Beck et al 2007a, Ryan et al 2007). De Luca (1997) has suggested that the surface EMG–force relationships reflects the concurrent increases in motor unit recruitment and motor unit firing rates that regulate muscle force output. "
    [Show abstract] [Hide abstract] ABSTRACT: The present study applied a log-transformation model to compare the electromyographic (EMG) amplitude versus torque relationships from monopolar EMG signals up to 35 mm proximal and distal from the innervation zone (IZ). Seven men (age = 23 ± 2 year; mass = 82 ± 10 kg) and two women (age = 21 ± 1 year; mass = 62 ± 8 kg) performed isometric ramp contractions of the right leg extensors with an eight-channel linear electrode array positioned over the vastus lateralis with the IZ located between channels 4 and 5. Linear regression models were fit to the log-transformed monopolar EMG(RMS)-torque relationships with the b terms (slope) and the a terms (Y-intercept) calculated for each channel and subject. The b terms for channels 4, 5, and 6 were higher (P ≤ 0.05) than the more distal channels 7 and 8 (P < 0.05). In contrast, there were no differences (P > 0.05) among the a terms of the eight channels. Thus, the shapes of the monopolar EMG(RMS)-torque relationships were altered as a function of distance between the IZ and recording area, which may be helpful for clinicians and researchers who infer changes in motor control strategies based on the shapes of the EMG(RMS)-torque relationships.
    Full-text · Article · Mar 2013
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