Effect of sex on torque, recovery, EMG, and MMG responses to fatigue.

OBJECTIVE: The purpose of the present investigation was to examine the effect of sex on maximal voluntary isometric contraction (MVIC) torque and the EMG and MMG responses as a result of fatiguing, intermittent, submaximal (65% of MVIC), isometric elbow flexion muscle contractions. METHODS: Eighteen men and women performed MVIC trials before (pretest), after (posttest), and 5-min after (5-min recovery) performing 50 intermittent, submaximal isometric muscle contractions. Surface electromyographic (EMG) and mechanomyographic (MMG) signals were simultaneously recorded from the biceps brachii muscle. RESULTS: As a result of the fatiguing workbout torque decreased similarly from pretest to posttest for both the men (24.0%) and women (23.3%). After 5-min of recovery, torque had partially recovered for the men, while torque had returned to pretest levels for the women. For both sexes, from pretest to posttest EMG mean power frequency and MMG amplitude decreased, but returned to pretest levels after 5-min of recovery. CONCLUSIONS: In the present study, there were sex-related differences in muscle fatigue that were not associated with the EMG or MMG responses.

Effects of fatiguing constant versus alternating intensity intermittent isometric muscle actions on maximal torque and neuromuscular responses.

OBJECTIVE: To determine the effects of constant versus alternating applications of torque during fatiguing, intermittent isometric muscle actions of the leg extensors on maximal voluntary isometric contraction (MVIC) torque and neuromuscular responses. METHODS: Sixteen subjects performed two protocols, each consisting of 50 intermittent isometric muscle actions of the leg extensors with equal average load at a constant 60% MVIC or alternating 40 then 80% (40/80%) MVIC with a work-to-rest ratio of 6-s on and 2-s off. MVIC torque as well as electromyographic signals from the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) and mechanomyographic signals from the VL were recorded pretest, immediately posttest, and 5-min posttest. RESULTS: The results indicated that there were no time-related differences between the 60% MVIC and 40/80% MVIC protocols. The MVIC torque decreased posttest (22 to 26%) and remained depressed 5-min posttest (9%). There were decreases in electromyographic frequency (14 to 19%) and mechanomyographic frequency (23 to 24%) posttest that returned to pretest levels 5-min posttest. There were no changes in electromyographic amplitude and mechanomyogrpahic amplitude. CONCLUSIONS: These findings suggested that these neuromuscular parameters did not track the fatigue-induced changes in MVIC torque after 5-min of recovery.

Four weeks of high- versus low-load resistance training to failure on the rate of torque development, electromechanical delay, and contractile twitch properties.

The purpose of this study was to investigate the effects of 4-weeks of high- versus low-load resistance training to failure on rate of torque development (RTD), electromechanical delay (EMD), and contractile twitch characteristics. Fifteen men (mean±SD; age=21.7±2.4 yrs) were randomly assigned to either a high- (80% 1RM; n=7) or low-load (30% 1RM; n=8) training group and completed elbow flexion resistance training to failure 3 times per week for 4 weeks. The participants were tested at baseline, 2-, and 4-weeks of training. Peak RTD (pRTDV) and RTD at 0-30 (RTD30V), 0-50 (RTD50V), 0-100 (RTD100V), and 0-200 (RTD200V) ms, integrated EMG amplitude (iEMG) at 0-30, 0-50, and 0-100 ms, and EMD were quantified during maximal voluntary isometric muscle actions. Peak twitch torque, peak RTD, time to peak twitch, 1/2 relaxation time and the peak relaxation rate were quantified during evoked twitches. Four weeks of high-load, but not low-load resistance training, increased RTD200V. There were also increases in iEMG during the first 30 ms of muscle activation for the high- and low-load groups, which may have indirectly indicated increases in early phase motor unit recruitment and/or firing frequency. There were no significant training-induced adaptations in EMD or contractile twitch properties.

Electromyographic Responses from the Vastus Medialis during Isometric Muscle Actions.

This study examined the electromyographic (EMG) responses from the vastus medialis (VM) for electrodes placed over and away from the innervation zone (IZ) during a maximal voluntary isometric contraction (MVIC) and sustained, submaximal isometric muscle action. A linear electrode array was placed on the VM to identify the IZ and muscle fiber pennation angle during an MVIC and sustained isometric muscle action at 50% MVIC. EMG amplitude and frequency parameters were determined from 7 bipolar channels of the electrode array, including over the IZ, as well as 10 mm, 20 mm and 30 mm proximal and distal to the IZ. There were no differences between the channels for the patterns of responses for EMG amplitude or mean power frequency during the sustained, submaximal isometric muscle action; however, there were differences between channels during the MVIC. The results of the present study supported the need to standardize the placement of electrodes on the VM for the assessment of EMG amplitude and mean power frequency. Based on the current findings, it is recommended that electrode placements be distal to the IZ and aligned with the muscle fiber pennation angle during MVICs, as well as sustained, submaximal isometric muscle actions.

Physiological Responses during Cycle Ergometry at a Constant Perception of Effort.

13 subjects performed an incremental test to exhaustion, 4, 8-min submaximal rides, and a 1-h ride at the rating of perceived exertion (RPE) that corresponded to the physical working capacity at the OMNI threshold (PWC(OMNI)) to examine: 1) the oxygen consumption (V̇O2), heart rate (HR), minute ventilation (+V̇(E)), respiratory frequency (FR), and power output responses during 1-h work bouts at a constant RPE that corresponded to the PWC(OMNI); and 2) the ability of current models to explain the responses for physiological and perceptual parameters during the 1-h work bouts. The RPE that corresponded to the PWC(OMNI) represented a sustainable exercise intensity (56±5% (V̇O(2Peak)) within the moderate-intensity domain. The mean, normalized slope coefficients for the V̇O2, +V̇(E), and power output vs. time relationships during the 1-h rides were significantly less than zero. The mean, normalized slope coefficient for the FR vs. time relationship during the 1-h rides, however, was not significantly different from zero. Thus, RPE most clearly tracked FR responses during the 1-h rides. It was hypothesized that afferent feedback from respiratory muscles may have mediated the perception of effort during cycle ergometry at a constant RPE in the moderate-intensity domain.

The rate of torque development: a unique, non-invasive indicator of eccentric-induced muscle damage?

This study examined the time courses of recovery for isometric peak torque and rate of torque development (RTD) after eccentric-induced muscle damage. 18 men completed 6 sets of 10 maximal eccentric isokinetic muscle actions at 30° · s(-1). Peak torque, peak RTD and RTD at 10 (RTD10), 50 (RTD50), 100 (RTD100) and 200 ms (RTD200), serum creatine kinase and lactate dehydrogenase were measured before (PRE), immediately after (POST), 24, 48 and 72 h after eccentric exercise. Creatine kinase and lactate dehydrogenase increased from 139 to 6 457 and from 116 to 199 IU · L(-1) from PRE to 72 h, respectively. Peak torque and all RTDs decreased at POST. Peak torque and RTD200 remained lower than PRE through 72 h. Peak RTD remained lower than PRE through 48 h, but was not different from PRE at 72 h. RTD10 and RTD100 were lower than PRE through 24 h, but were not different from PRE at 48 and 72 h. RTD50 decreased at POST, but was not different from PRE at 24 h. Early phase RTDs recovered more quickly than PT and RTD200. Early phase RTDs may reflect neural mechanisms underlying eccentric-induced force decrements, while late RTDs may describe the same physiological mechanisms as PT.

The effect of epoch length on the electromyographic mean power frequency and amplitude versus time relationships.

UNLABELLED: The electromyographic (EMG) mean power frequency (MPF) and amplitude versus time relationships are commonly used to characterize localized muscle fatigue. PURPOSE: The purpose of this study was to compare the effect of epoch length on the individual and mean slope coefficients and y-intercepts resulting from the EMG MPF and amplitude versus time relationships of the vastus medialis (VM) muscle during fatiguing isometric muscle actions at 30 and 75% of maximum voluntary isometric contraction (MVC). METHODS: Eight adults performed two continuous, isometric muscle actions of the leg extensors at 30 and 75% MVC to exhaustion. Six, 5.0 s epochs of the surface EMG signals were recorded from the VM during each minute. Epoch lengths of 0.5, 1.0, and 2.0 s were selected from the middle of each 5.0 s epoch. Linear regression was used to estimate the slope coefficient and y-intercept values for the EMG MPF and amplitude versus time relationships for each epoch length (0.5, 1.0, 2.0, and 5.0 s) and subject. RESULTS: There were no significant differences between epoch lengths for the individual or mean slope coefficients or y-intercepts (EMG MPF and amplitude versus time relationships). CONCLUSION: This study indicated that epochs of 0.5 - 5.0 s resulted in the same characterization of EMG (MPF and amplitude) versus time relationships during isometric muscle actions.

A mechanomyographic fatigue threshold test for cycling.

The purposes of this study were twofold: 1) to derive the mechanomyographic mean power frequency fatigue threshold (MMG MPFFT) for submaximal cycle ergometry; and 2) to compare the power outputs associated to the MMG MPFFT to other neuromuscular and gas exchange fatigue thresholds. 9 adults (5 men and 4 women; mean+/-SD age=23.7+/-3.7 years; body weight=66.3+/-8.2 kg) performed an incremental cycle ergometry test to exhaustion while expired gas samples, electromyographic (EMG), and MMG signals were measured from the vastus lateralis muscle. The non-significant correlations (r=0.17 to 0.66; p>0.05) among the physical working capacity at the fatigue threshold (PWCFT), MMG MPFFT, and gas exchange threshold (GET) suggested that different physiological mechanisms may underlie these 3 fatigue thresholds. A significant correlation (r=0.83) for the MPFFT vs. respiratory compensation point (RCP) suggested that these fatigue thresholds may be mediated by a common physiological mechanism. In addition, the significantly lower mean values found for the PWCFT (mean+/-SD=163+/-43 W), MMG MPFFT (132+/-33 W), and GET (144+/-28 W) than MPFFT (196+/-53 W) and RCP (202+/-41 W) suggested that these gas exchange and neuromuscular fatigue thresholds may demarcate different exercise intensity domains.

The effects of parallel versus perpendicular electrode orientations on EMG amplitude and mean power frequency from the biceps brachii.

The purposes of this study were threefold: (1) to compare the isometric torque-related patterns of absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) responses for electrode orientations that were parallel and perpendicular to the muscle fibers; (2) to examine the influence of electrode orientation on mean absolute EMG amplitude and MPF values; and (3) to determine the effects of normalization on mean EMG amplitude and MPF values from parallel and perpendicular electrode orientations. Ten adults (5 men and 5 women mean +/- SD age = 23.8 +/- 2.3 years) volunteered to participate in the investigation. Two sets of bipolar surface EMG electrodes (20 mm center to center) were placed parallel and perpendicular to the muscle fibers over the biceps brachii. The subjects performed a maximal voluntary isometric contraction (MVIC) test followed by randomly ordered submaximal muscle actions in 10% increments from 10 to 90% MVIC. Paired t-tests indicated that absolute EMG amplitude values for the parallel electrode orientation were greater (p < 0.05) than those for the perpendicular orientation at all isometric torque levels except 10% MVIC For normalized EMG amplitude values, however, there were no significant mean differences between electrode orientations. There were also no differences between electrode orientations for absolute or normalized EMG MPF values. In 30% of the cases, different torque-related patterns of responses were observed between the parallel and perpendicular electrode orientations for the absolute and normalized EMG amplitude and MPF values. Therefore, the results of the present study support the need for standardizing electrode orientation to compare the pattern of responses for EMG amplitude and MPF values and normalizing EMG amplitude data to compare the mean values.

Wavelet-based analysis of surface mechanomyographic signals from subjects with differences in myosin heavy chain isoform content.

The purpose of this study was to use a wavelet analysis designed specifically for surface mechanomyographic (MMG) signals to determine if the % myosin heavy chain (MHC) isoform content affected the shape of the MMG frequency spectrum during isometric muscle actions. Five resistance-trained (mean +/- SD age = 23.2 +/-3.7 yrs), five aerobically-trained (mean +/- SD age = 32.6 +/- 5.2 yrs), and five sedentary (mean +/- SD age = 23.4 +/- 4.1 yrs) men performed isometric muscle actions of the dominant leg extensors at 20%, 40%, 60%, 80%, and 100% of the maximum voluntary contraction (MVC). Surface MMG signals were detected from the vastus lateralis during each muscle action and processed with the MMG wavelet analysis. In addition, muscle biopsies were taken from the vastus lateralis and analyzed for % MHC isoform content. The results showed that there were distinct differences among the three groups of subjects for % MHC isoform content. These differences were not manifested, however, in the isometric force-related changes in the total intensity of the MMG signal in each wavelet band. It is possible that factors such as the thicknesses of the subcutaneous adipose tissue and/or iliotibial band reduced the potential influence of differences in % MHC isoform content on the MMG signal.

The effect of pedaling cadence and power output on mechanomyographic amplitude and mean power frequency during submaximal cycle ergometry.

The purpose of this study was to examine the effects of power output and pedaling cadence on the amplitude and mean power frequency (MPF) of the mechanomyographic (MMG) signal during submaximal cycle ergometry. Nine adults (mean age +/- SD = 22.7 +/- 2.1 yrs) performed an incremental (25 W increase every min) test to exhaustion on an electronically braked cycle ergometer to determine VO2Peak and Wpeak. The subjects also performed three, 8 min continuous, constant power output rides (randomly ordered) at 35%, 50%, and 65% Wpeak. The continuous 8 min workbouts were divided into 4 min epochs. The subjects pedaled at either 50 or 70 rev x min(-1) (randomized) during the first 4 min epoch, then changed to the alternate cadence during the second 4 min epoch. The MMG signal was recorded from the vastus lateralis during the final 10 s of each minute. Two separate two-way [cadence (50 and 70 rev x min(-1)) x %Wpeak (35, 50, and 65)] repeated measures ANOVAs indicated that MMG amplitude followed power output, but not pedaling cadence, whereas MMG MPF was not consistently affected by power output or pedaling cadence. Furthermore, these findings suggested that power output was modulated by motor unit recruitment and not rate coding.

The influence of muscle fiber type composition on the patterns of responses for electromyographic and mechanomyographic amplitude and mean power frequency during a fatiguing submaximal isometric muscle action.

The purpose of this investigation was to examine the influence of muscle fiber type composition on the patterns of responses for electromyographic (EMG) and mechanomyographic (MMG) amplitude and mean power frequency (MPF) during a fatiguing submaximal isometric muscle action. Five resistance-trained (mean +/- SD age = 23.2 +/- 3.7 yrs) and five aerobically-trained (mean +/- SD age = 32.6 +/- 5.2 yrs) men volunteered to perform a fatiguing, 30-sec submaximal isometric muscle action of the leg extensors at 50% of the maximum voluntary contraction (MVC). Muscle biopsies from the vastus lateralis revealed that the myosin heavy chain (MHC) composition for the resistance-trained subjects was 59.0 +/- 4.2% Type IIa, 0.1 +/- 0.1% Type IIx, and 40.9 +/- 4.3% Type I. The aerobically-trained subjects had 27.4 +/- 7.8% Type IIa, 0.0 +/- 0.0% Type IIx, and 72.6 +/- 7.8% Type I MHC. The patterns of responses and mean values for absolute and normalized EMG amplitude and MPF during the fatiguing muscle action were similar for the resistance-trained and aerobically-trained subjects. The resistance-trained subjects demonstrated relatively stable levels for absolute and normalized MMG amplitude and MPF across time, but the aerobically-trained subjects showed increases in MMG amplitude and decreases in MMG MPE The absolute MMG amplitude and MPF values for the resistance-trained subjects were also greater than those for the aerobi-cally-trained subjects. These findings suggested that unlike surface EMG, MMG may be a useful noninvasive technique for examining fatigue-related differences in muscle fiber type composition.

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

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.

Is fatigue all in your head? A critical review of the central governor model.

The central governor model has recently been proposed as a general model to explain the phenomenon of fatigue. It proposes that the subconscious brain regulates power output (pacing strategy) by modulating motor unit recruitment to preserve whole body homoeostasis and prevent catastrophic physiological failure such as rigor. In this model, the word fatigue is redefined from a term that describes an exercise decline in the ability to produce force and power to one of sensation or emotion. The underpinnings of the central governor model are the refutation of what is described variously as peripheral fatigue, limitations models, and the cardiovascular/anaerobic/catastrophe model. This argument centres on the inability of lactic acid models of fatigue to adequately explain fatigue. In this review, it is argued that a variety of peripheral factors other than lactic acid are known to compromise muscle force and power and that these effects may protect against "catastrophe". Further, it is shown that a variety of studies indicate that fatigue induced decreases in performance cannot be adequately explained by the central governor model. Instead, it is suggested that the concept of task dependency, in which the mechanisms of fatigue vary depending on the specific exercise stressor, is a more comprehensive and defensible model of fatigue. This model includes aspects of both central and peripheral contributions to fatigue, and the relative importance of each probably varies with the type of exercise.

Comparison of Fourier and wavelet transform procedures for examining mechanomyographic and electromyographic frequency versus isokinetic torque relationships.

The purpose of this study was to compare the isokinetic torque-related patterns for mechanomyographic (MMG) and electromyographic (EMG) center frequency [wavelet center frequency (CF), mean power frequency (MPF), and median frequency (MDF)] determined by the fast Fourier transform (FFT) and discrete wavelet transform (DWT). Ten adults [mean +/- SD age = 22.0 +/- 3.4 yrs] performed submaximal to maximal, isokinetic muscle actions of the biceps brachii on a Cybex II dynamometer. For both MMG and EMG, the CF, MPF, and MDF values were intercorrelated at (r = 0.91-0.98). Quadratic models provided the best fit for the absolute and normalized CF, MPF, and MDF versus isokinetic torque relationships for MMG (R2 = 0.67-0.83) and EMG (R2 = 0.72-0.90). The similarities among the CF, MPF, and MDF patterns suggested that Fourier or wavelet transform procedures can be used to examine the patterns of MMG and EMG responses during dynamic muscle actions.

The acute effects of static stretching on peak torque, mean power output, electromyography, and mechanomyography.

The purpose of this study was to examine the acute effects of static stretching on peak torque (PT), the joint angle at PT, mean power output (MP), electromyographic (EMG) amplitude, and mechanomyographic (MMG) amplitude of the vastus lateralis (VL) and rectus femoris (RF) muscles during maximal, voluntary concentric isokinetic leg extensions at 60 and 240 degrees x s(-1) of the stretched and unstretched limbs. Twenty-one volunteers [mean age (SD) 21.5 (1.3) years] performed maximal, voluntary concentric isokinetic leg extensions for the dominant and non-dominant limbs at 60 and 240 degrees x s(-1). Surface EMG (muVrms) and MMG (mVrms) signals were recorded from the VL and RF muscles during the isokinetic tests. PT (Nm), the joint angle at PT, and MP (W) were calculated by a dynamometer. Following the initial isokinetic tests, the dominant leg extensors were stretched using four static stretching exercises. After the stretching, the isokinetic tests were repeated. PT decreased (P< or =0.05) from pre- to post-stretching for the stretched limb at 60 and 240 degrees x s(-1) and for the unstretched limb at 60 degrees x s(-1). EMG amplitude of the VL and RF also decreased (P< or =0.05) from pre- to post-stretching for the stretched and unstretched limbs. There were no stretching-induced changes (P>0.05) for the joint angle at PT, MP, or MMG amplitude. These findings indicated stretching-induced decreases in force production and muscle activation. The decreases in PT and EMG amplitude for the unstretched limb suggested that the stretching-induced decreases may be due to a central nervous system inhibitory mechanism.

Mechanomyographic and electromyographic amplitude and frequency responses during fatiguing isokinetic muscle actions of the biceps brachii.

The purpose of this investigation was to examine the mechanomyographic (MMG) and electromyographic (EMG) amplitude and mean power frequency (MPF) patterns during fatiguing isokinetic muscle actions of the biceps brachii. Ten adults [three women (mean +/- SD age = 20 +/- 2 yrs) and seven men (mean +/- SD age = 23 +/- 3 yrs) ] volunteered to perform 50 consecutive maximal, concentric isokinetic muscle actions of the biceps brachii at 180 degrees x s(-1). The percent decline (mean +/- SD) in isokinetic peak torque (PT) was 70 +/- 17% and polynomial regression analyses indicated a cubic relationship (R2 = 0.994) between PT and repetition number. Both MMG amplitude and MMG MPF decreased linearly (r2 = 0. 774 and 0.238, respectively) across repetitions. The results for EMG amplitude demonstrated a cubic (R2 = 0.707) pattern across repetitions, where EMG amplitude increased during repetitions 1-20, remained stable during repetitions 20-40, and increased during repetitions 40-50. There was a quadratic (R2 = 0. 939) reduction in EMG MPF throughout the test. The decreases in MMG amplitude and MMG MPF may have been due to de-recruitment of fast fatiguing motor units, a reduction in muscular compliance, or the effects of "muscle wisdom." The results for EMG amplitude may have reflected nonmaximal efforts by the subjects and/or peripheral fatigue. The factor(s) determining the decrease in EMG MPF are unclear, although a reduction in muscle fiber action potential conduction velocity may have been partially responsible.

Mechanomyographic time and frequency domain responses of the vastus medialis muscle during submaximal to maximal isometric and isokinetic muscle actions.

The purpose of this study was to examine the patterns for the mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus torque relationships during isometric and isokinetic muscle actions. Ten adults (mean age +/- SD = 22 +/- 1 y) volunteered to perform isometric and isokinetic leg extension muscle actions at 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100% of peak torque on a Cybex II dynamometer. A piezoelectric crystal contact sensor was placed on the vastus medialis to detect the MMG signal. Regression analyses indicated that for the isometric muscle actions, the relationships for MMG amplitude (R2 = 0.998) and MPF (R2 = 0.987) versus torque were cubic. For the isokinetic muscle actions, the relationships for MMG amplitude (r2 = 0.927) and MPF (r2 = 0.769) versus torque were linear. The different patterns for MMG amplitude and frequency may reflect differences in the motor control strategies that modulate torque production for isometric versus dynamic muscle actions.

Cross-correlation analyses of mechanomyographic signals from the superficial quadriceps femoris muscles during concentric and eccentric isokinetic muscle actions.

The purpose of this investigation was to examine the cross-correlation coefficients of mechanomyographic (MMG) signals recorded from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles during maximal, concentric and eccentric isokinetic muscle actions. Eleven females (mean +/- SD age = 21 +/- 1 yr) performed such muscle actions of the leg extensors at 60 degrees.s-1 on a Cybex 6000 dynamometer. MMG signals were sampled simultaneously from the VL, RF, and VM at 1000 Hz by piezoelectric crystal contact sensors. Peak composite cross-correlation coefficients (rxy) and common variances (rxy2) were determined for each between-muscle comparison (VL vs. RF, VL vs. VM, and RF vs. VM). The results indicated peak cross-correlation coefficients ranging from rxy = 0.38 to 0.52, while common variances (rxy2) between signals ranged from 14% to 27% across all time lags (tau = -50...). In conjunction with other studies, these results suggested that despite the potential for some cross-talk, MMG measurements can be used to examine differences between the patterns of MMG amplitude and frequency responses of the superficial quadriceps femoris muscles.

Mechanomyographic and electromyographic amplitude and frequency responses from the superficial quadriceps femoris muscles during maximal, eccentric isokinetic muscle actions.

The purposes of this study were to examine the effects of gender and muscle (vastus lateralis = VL, rectus femoris = RF, and vastus medialis = VM) on the velocity-related patterns for peak torque (PT), mean power output (MP), mechanomyographic (MMG) amplitude, electromyographic (EMG) amplitude, MMG mean power frequency (MPF), and EMG MPF during maximal, eccentric isokinetic muscle actions. Thirteen females (mean +/- SD age = 21 +/- 1 years) and eleven males (mean +/- SD age = 21 +/- 2 years) volunteered for this investigation. PT and MP were measured on a calibrated Cybex 6000 dynamometer at randomly ordered velocities of 60, 120, and 180 degrees.s-1, while MMG and EMG signals were recorded simultaneously from the VL, RF, and VM muscles. The results indicated no gender-related differences for the patterns of PT, MP, MMG amplitude, EMG amplitude, MMG MPF, or EMG MPF. Furthermore, no muscle-related differences were found for the patterns of MMG amplitude, EMG amplitude, or MMG MPF. The normalized values for MP and MMG amplitude increased from 60 to 180 degrees.s-1 (60 degrees.s-1 < 120 degrees.s-1 < 180 degrees.s-1). PT and EMG MPF remained unchanged across velocity, while EMG amplitude remained unchanged from 60 to 120 degrees.s-1, but decreased (approximately 10%) from 120 to 180 degrees.s-1. The findings indicated a close association between the patterns for MP and MMG amplitude, and a similarity between the patterns for PT, EMG amplitude, and EMG MPF across velocity. Therefore, the present findings suggested that motor unit recruitment (EMG amplitude), firing rate (MMG MPF), and muscle fiber action potential conduction velocity (EMG MPF) exhibited velocity-related patterns that were similar to PT production, while MMG amplitude was more closely associated with MP.