Comparison of mechanomyographic sensors during incremental cycle ergometry for the quadriceps femoris

The purpose of this study was to examine the mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus power output relationships for the vastus lateralis and rectus femoris muscles during incremental cycle ergometry between the piezoelectric contact sensor (HP) and the accelerometer (ACC) sensor. Nine men performed an incremental cycle ergometry test to voluntary exhaustion. Polynomial regression analyses on a subject‐by‐subject basis indicated that the relationship between the normalized MMG amplitude versus normalized power output was best fit with either a linear, quadratic, or cubic model. These patterns were consistent between sensors for each muscle for each subject. No consistent relationship was found for MMG MPF within subjects and between muscle groups. In addition, there were no significant sensor × power output interactions for normalized MMG amplitude or MPF. These results suggest that, for cycle ergometry, the HP and ACC sensors provide similar information for the interpretation of motor control strategies during continuous exercise. Muscle Nerve, 2010     

Linearity and reliability of the mechanomyographic amplitude versus dynamic torque relationships for the superficial quadriceps femoris muscles

The purpose of this investigation was to examine the linearity and reliability of the mechanomyographic (MMG) amplitude versus dynamic torque relationships for the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Nine healthy men and 11 healthy women performed submaximal to maximal, concentric, isokinetic muscle actions of the leg extensors at 30° s^?1 on two occasions. Surface MMG signals were detected from the VL, RF, and VM of the dominant thigh during both trials. The ranges of the coefficients of determination for the MMG amplitude versus dynamic torque relationships were 0.01–0.94 for the VL, 0.01–0.84 for the RF, and 0.19–0.96 for the VM. The intraclass correlation coefficients for the linear MMG amplitude versus torque slope coefficients were 0.823 (VL), 0.792 (RF), and 0.927 (VM). These results indicate that, when analyzed for individual subjects, the MMG amplitude versus dynamic torque relationships demonstrated inconsistent linearity. When using MMG in the clinical setting, dynamic muscle actions of the superficial quadriceps femoris muscles do not appear to be appropriate for assessing changes in muscle function during strength training. Muscle Nerve, 2009     

The effects of innervation zone on electromyographic amplitude and mean power frequency during incremental cycle ergometry

The purpose of this study was to examine the effects of electrode placements over the innervation zone (IZ), as well as proximal and distal to the IZ, on the patterns for the absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) versus power output relationships during incremental cycle ergometry. Fifteen men [mean +/- S.D. age = 24.3 +/- 2.4 years; VO2max = 47.3 +/- 4.9 ml kg(-1) min(-1)] performed incremental cycle ergometry tests to exhaustion. Surface EMG signals were recorded simultaneously from bipolar electrode arrangements placed on the vastus lateralis (VL) muscle over the IZ, as well as proximal and distal to the IZ. Polynomial regression analyses were used to describe the relationships for absolute and normalized EMG amplitude (microVrms and %max) and MPF (Hz and %max) versus power output (%max) for each subject at the three electrode placement sites. In addition, separate one-way repeated measures ANOVAs were used to examine mean differences between the three sites for absolute and normalized EMG amplitude and MPF at power outputs of 80, 110, 140, and 170 W. The results of the polynomial regression analyses revealed that the best fit model for each site for the absolute and normalized EMG amplitude versus power output relationship was linear for 11 subjects and quadratic for 2 subjects. The remaining two subjects exhibited both linear and quadratic patterns that were site-dependent. For EMG MPF, 10 subjects exhibited significant relationships (linear and/or quadratic) across power outputs for at least one site. In addition, there were significant (P < 0.05) mean differences between the electrode placement sites for absolute EMG amplitude, but not absolute EMG MPF at 80, 110, 140, and 170 W. There were no significant (P > 0.05) mean differences, however, between the three sites for normalized EMG amplitude or MPF at 80, 110, 140, and 170 W. These findings indicated that the placement of bipolar electrodes over the IZ, as well as proximal and distal to the IZ, had no effect on the pattern of the normalized EMG amplitude versus power output relationship or the mean normalized EMG amplitude and MPF values. Thus, during cycle ergometry, normalized EMG amplitude values (but not absolute values) can be compared between studies that have utilized various electrode placement sites on the VL.     

Reliability of the log‐transformed EMG amplitude‐power output relationship for incremental knee‐extensor ergometry

Introduction: The purpose of this investigation was to determine the reproducibility of the log‐transformed model for electromyography (EMG) amplitude during incremental single‐leg knee‐extensor exercise. Methods: Eight healthy college‐aged men performed 3 incremental tests on separate occasions on a knee‐extensor ergometer. EMG amplitude was analyzed for each participant on each occasion for the rectus femoris and vastus medialis muscles at 4 different exercise power outputs (30%, 50%, 70%, and 90%) corresponding to each participant's maximal power output. Intraclass correlation coefficients (ICC) were determined for the slope and y‐intercept terms derived from the log‐transformed EMG amplitude‐power output relationship for each muscle. Results: The ICC values for the rectus femoris (slope = 0.779; y‐intercept = 0.787) and vastus medialis (slope = 0.756; y‐intercept = 0.763) muscles were high. Conclusions: The log‐transformed EMG amplitude‐power output relationship is a reliable index for measuring motor unit activation. Muscle Nerve 52:428–434, 2015     

Electromyographic responses of the superficial quadriceps femoris muscles during incremental treadmill running

Introduction: We examined the individual patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during incremental treadmill running. Methods: Nine physically active men performed incremental treadmill running at a constant grade of 1%. The EMG signal was recorded from the 3 superficial quadriceps femoris muscles during the work bout. Results: The results of the polynomial regression indicated that the linear model best fit the data for the composite data for all 3 muscles and the majority (7 of 9) of subjects. There were no consistent patterns of responses for the EMG MPF responses. Also, there were no significant (P > 0.05) muscle × running velocity interactions for EMG amplitude and MPF. Conclusions: These results indicate consistent patterns of responses for EMG amplitude during incremental treadmill running, regardless of which muscle was studied. Muscle Nerve 48 : 938–944, 2013     

Excess post-exercise oxygen consumption is not associated with mechanomyographic amplitude after incremental cycle ergometry in the quadriceps femoris muscles

Introduction: The purpose of this study was to understand the relationship between the mechanical activities of the three superficial quadriceps muscles and excess post‐exercise oxygen consumption (EPOC) after incremental cycle ergometer exercise. Methods: Twelve healthy male volunteers had mechanomyographic (MMG) and electromyographic (EMG) activity of the superficial quadriceps muscles recorded 30 minutes before incremental cycle ergometry and 60 minutes after the exercise work bout. Results: The results indicate significant time‐constant values for EPOC and MMG amplitude for the three superficial quadriceps muscles during the 60‐minute post‐exercise recovery period. For EMG amplitude no decay patterns were found for the three muscles. In addition, there were no mean differences between the MMG values for the three muscles that were significantly different from EPOC. Conclusions: These results suggest that EPOC after exercise could not be exclusively attributed to elevated activity of the working muscles. Muscle Nerve 44: 432–438, 2011     

MMG and EMG responses during fatiguing isokinetic muscle contractions at different velocities

The purpose of this study was to determine mechanomyographic (MMG) and electromyographic (EMG) responses of the superficial quadriceps muscles during repeated isokinetic contractions in order to provide information about motor control strategies during such activity, and to assess uniformity in mechanical activity (MMG) between the investigated muscles. Ten adults performed 50 maximal concentric muscle contractions at three randomly selected contraction velocities (60, 180, and 300 degrees.s(-1)) on different days. Surface electrodes and an MMG sensor were placed on the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). EMG and MMG amplitude and peak torque (PT) were calculated for each contraction, normalized, and averaged across all subjects. The results demonstrated that MMG amplitude more closely tracked the fatigue-induced decline in torque production at each velocity than did EMG amplitude. This indicates that MMG amplitude may be useful for estimating force production during fatiguing dynamic contractions when a direct measure is not available, such as during certain rehabilitative exercises. MMG amplitude responses of the VL, RF, and VM were not uniform for each velocity or across velocities, indicating that it may be possible to detect the individual contribution of each muscle to force production during repeated dynamic contractions. Therefore, MMG amplitude may be clinically useful for detecting abnormal force contributions of individual muscles during dynamic contractions, and determining whether various treatments are successful at correcting such abnormalities.     

EMG spectral differences among the quadriceps femoris during the stretch reflex

Introduction: The purpose of this study was to examine the electromyographic (EMG) spectral characteristics of the quadriceps femoris muscles during tendon tap stretch reflexes. Methods: Sixteen healthy subjects (mean ± SD age = 21.2 ± 2.8 years) performed tendon tap reflexes of the leg extensors as surface EMG signals were detected from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles of the dominant thigh. All EMG signals were processed with a wavelet analysis, and the resulting spectra were decomposed with nonparametric spectral decomposition. Results: The results showed that the spectra for the VL had significantly more high‐frequency power than those for the RF and VM, with similar spectral shapes for the RF and VM. Conclusions: These findings could be due to differences in the width of the innervation zone, or the fiber type composition of the muscles, although the latter seems to be more likely. Muscle Nerve 52 : 826–831, 2015     

The effects of interelectrode distance on electromyographic amplitude and mean power frequency during incremental cycle ergometry

The purpose of this study was to examine the effects of interelectrode distance (IED) on the relationships of absolute and normalized EMG amplitude and mean power frequency (MPF) versus power output during incremental cycle ergometry. Eleven adults (mean +/- S.D. age = 24.2 +/- 2.6 y; V(O2max) = 49.4 +/- 8.3 ml kg(-1) min(-1)) performed incremental cycle ergometry tests. Surface EMG signals were recorded simultaneously from bipolar electrode arrangements placed over the VL muscle with IEDs of 20, 40, and 60 mm. Polynomial regression analyses were used to describe the relationships for absolute and normalized EMG amplitude (muV(rms) and % max) and MPF (Hz and % max) versus power output (%max) for each subject at the three IEDs. In addition, separate one-way repeated measures ANOVAs were used to examine mean differences between the three IEDs for absolute and normalized EMG amplitude and MPF at power outputs of 80, 110, 140, and 170 W. The results of the polynomial regression revealed that the best fit model for each IED for the absolute and normalized EMG amplitude was linear for six of the 11 subjects and quadratic for five of the subjects. For EMG MPF, four of the 11 subjects exhibited significant relationships (linear or quadratic) across power outputs for at least one IED. The one-way repeated measures ANOVAs revealed significant mean differences between the IEDs for absolute EMG amplitude and MPF at 80, 110, 140, and 170 W. There were no significant mean differences, however, between the IEDs for normalized EMG amplitude or MPF at 80, 110, 140, and 170 W. The results of the study indicated that there were no consistent patterns of responses between individual subjects for EMG amplitude or MPF versus power output relationships for IEDs of 20, 40, and 60 mm during incremental cycle ergometry. The current findings supported the process of normalization for EMG amplitude and MPF data obtained during cycle ergometry when comparisons are made for different IEDs.     

Mechanomyographic amplitude and mean power output during maximal, concentric, isokinetic muscle actions

The purpose of this study was to determine the velocity-related patterns for mechanomyographic (MMG) amplitude, electromyographic (EMG) amplitude, mean power output (MP), and peak torque (PT) of the superficial muscles of the quadriceps femoris (vastus lateralis [VL], rectus femoris [RF], and vastus medialis [VM]) during maximal, concentric, isokinetic leg extensions. Twelve adult women (mean +/- SD: 22 +/- 3 years of age) performed such leg extensions at velocities of 60 degrees, 120 degrees, 180 degrees, 240 degrees, and 300 degrees /s on a Cybex 6000 dynamometer. PT decreased (P < 0.05) across velocity to 240 degrees /s. MP and MMG amplitude for each muscle (VL, RF, and VM) increased (P < 0.05) with velocity to 240 degrees /s and then plateaued. EMG amplitude increased (P < 0.05) to 240°/s for the VL, remained unchanged across velocity (P > 0.05) for the RF, and increased (P < 0.05) to 300 degrees /s for the VM. The results indicated close similarities between the velocity-related patterns for MMG amplitude and MP, but dissociations among EMG amplitude, MMG amplitude, and PT. These findings support the recent hypothesis that MMG amplitude is more closely related to MP than PT during maximal, concentric, isokinetic muscle actions and, therefore, may be useful for monitoring training-induced changes in muscle power.     

Activation linearity and parallelism of the superficial quadriceps across the isometric intensity spectrum

The purpose of this study was to assess neuromuscular activation of the three superficial portions of the quadriceps femoris muscles during linearly increasing isometric contraction intensities. Thirty healthy volunteers were assessed for isometric electromyographic (EMG) activity of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles with the knee at 60 degrees of flexion. For 5 s, subjects performed isometric contractions equivalent to 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, and 90% of the average of three maximal voluntary contractions (MVC), in random order. Full-wave rectified and integrated EMG signals over the middle 3 s of each contraction were expressed as a percentage of the activity recorded during the three averaged MVCs. One sample t-tests and 95% confidence intervals were calculated at each relative torque level. A two-factor analysis of variance (muscle by intensity) with repeated measures was performed to evaluate parallel activation across the intensity levels. Activation linearity was assessed via regression analysis for each muscle. VM activation was shown to be significantly lower than expected at 20-70% MVC. VL and RF activations were significantly higher than expected at 10% MVC, and RF EMG was less than expected at 40-70% MVC. EMG of VM was shown to increase significantly more than VL and RF from 80% to 90% MVC. Significant linear and quadratic relations were also demonstrated for all three muscles. Parallel activation of the superficial quadriceps muscles occurred from low to moderate intensities, whereas convergence was noted at near maximal intensities.     

Mechanomyographic responses are not influenced by the innervation zone for the vastus medialis

Introduction: The purposes of this study were to: (1) compare the power output–related patterns of absolute and normalized mechanomyographic (MMG) amplitude and mean power frequency (MPF) signals across the innervation zone (IZ) during incremental cycle ergometry; and (2) examine the influence of the IZ on the mean MMG amplitude and MPF values. Methods: Ten men performed incremental cycle ergometry tests to exhaustion. Surface MMG signals were recorded simultaneously from accelerometer arrangements placed on the vastus medialis over the IZ and proximal and distal to the IZ. Results: The results of polynomial regression indicate that the best‐fit model for each site was consistent for each subject for MMG amplitude, but not for MMG MPF. Two‐way analyses of variance (ANOVAs) revealed no site × power output interaction (P > 0.05) for absolute and normalized MMG amplitude and MPF values. Conclusion: Our findings demonstrate that the IZ does not influence the MMG signal during dynamic exercise. Muscle Nerve 44: 424–431, 2011     

Twitch and M‐wave potentiation induced by intermittent maximal voluntary quadriceps contractions: Differences between direct quadriceps and femoral nerve stimulation

Introduction: The aim of this study was to investigate differences in twitch and M‐wave potentiation in the quadriceps femoris when electrical stimulation is applied over the quadriceps muscle belly versus the femoral nerve trunk. Methods: M‐waves and mechanical twitches were evoked using direct quadriceps muscle and femoral nerve stimulation between 48 successive isometric maximal voluntary contractions (MVC) from 10 young, healthy subjects. Potentiation was investigated by analyzing the changes in M‐wave amplitude recorded from the vastus medialis (VM) and vastus lateralis (VL) muscles and in quadriceps peak twitch force. Results: Potentiation of twitch, VM M‐wave, and VL M‐wave were greater for femoral nerve than for direct quadriceps stimulation (P < 0.05). Despite a 50% decrease in MVC force, the amplitude of the M‐waves increased significantly during exercise. Conclusions: In addition to enhanced electrogenic Na⁺‐K⁺ pumping, other factors (such as synchronization in activation of muscle fibers and muscle architectural properties) may significantly influence the magnitude of M‐wave enlargement. Muscle Nerve 48 : 920–929, 2013     

Utility of electromyographic fatigue threshold during treadmill running

Introduction: We investigated 2 different methods for determining muscle fatigue threshold by electromyography (EMG). Methods: Thirteen subjects completed an incremental treadmill running protocol for EMG fatigue threshold (EMG_FT) determination based on the critical power concept (EMG_FT1) and the breakpoint in the linear relationship between EMG amplitude and exercise intensity (EMG_FT2). Then, both the EMG_FT1 and EMG_FT2 were tested in a continuous treadmill running protocol. EMG was recorded from the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and lateral gastrocnemius (LG) muscles. Results: For BF, EMG_FT2 was higher than EMG_FT1, and EMG_FT1 for BF was lower than EMG_FT1 for LG. EMG of RF was higher at EMG_FT2 than at EMG_FT1, and LG EMG was lower at EMG_FT2. Conclusions: EMG_FT can be determined during a single treadmill running test, and EMG_FT1 may be the most appropriate method to estimate the muscle fatigue threshold during running. Muscle Nerve 52 : 1030–1039, 2015     

The influence of electrode placement over the innervation zone on electromyographic amplitude and mean power frequency versus isokinetic torque relationships

The purpose of this investigation was to examine the influence of electrode placement over the estimated innervation zone (IZ) for the vastus lateralis, as well as proximal and distal to the estimated IZ, on the torque-related patterns for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric and eccentric isokinetic muscle actions of the leg extensors. Eleven men performed randomly ordered, submaximal to maximal concentric and eccentric isokinetic muscle actions of the dominant leg extensors in 10% increments from 10 to 90% peak torque (PT). Surface EMG signals were recorded simultaneously from the vastus lateralis muscle with bipolar electrode arrangements placed over the estimated IZ, as well as proximal and distal to the estimated IZ. The results indicated that there were no consistent differences among the proximal, IZ, and distal electrode placement sites for the patterns of responses for absolute and normalized EMG amplitude and MPF versus torque, or the mean absolute and normalized EMG amplitude and MPF values. Thus, these findings suggested that during concentric and eccentric isokinetic muscle actions of the leg extensors, electrode placement over the estimated IZ for the vastus lateralis had no effect on the patterns of responses or mean values for absolute and normalized EMG amplitude and MPF versus torque.     

A comparison of monopolar and bipolar recording techniques for examining the patterns of responses for electromyographic amplitude and mean power frequency versus isometric torque for the vastus lateralis muscle

The purpose of the present study was to compare monopolar and bipolar recording techniques for the patterns of responses and mean values for absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) versus isometric torque for the vastus lateralis muscle. Ten healthy men (mean+/-S.D. age=23.6+/-3.0 years; body weight=80.9+/-15.6 kg) volunteered to perform submaximal to maximal isometric muscle actions of the dominant leg extensors. Monopolar and bipolar surface EMG signals were detected simultaneously from the vastus lateralis with an eight-channel linear electrode array. The results indicated that in 70-80% of the cases, monopolar and bipolar recording techniques resulted in the same patterns of responses for absolute and normalized EMG amplitude and MPF versus isometric torque. There were, however, differences between the two techniques for mean absolute EMG amplitude and MPF values, but not for the normalized values. Thus, these results supported the practice of normalization, and suggested that comparisons can be made between monopolar and bipolar recording methods for the patterns of responses and mean values for normalized (but not absolute) EMG amplitude and MPF versus isometric torque.     

Inter-individual variability in the torque-related patterns of responses for mechanomyographic amplitude and mean power frequency

The purpose of this study was to examine the inter-individual variability for the patterns of responses for mechanomyographic (MMG) amplitude and mean power frequency (MPF) versus isometric torque in lower-strength (LS) and higher-strength (HS) individuals. Twelve participants (mean +/- S.D. age = 25 + 4 years) performed two isometric maximal voluntary contractions (MVCs) before and after completing nine submaximal step muscle actions (15%, 25%, 35%, 45%, 55%, 65%, 75%, 85%, and 95% MVC) of the right leg extensors. MMG signals were recorded from the vastus lateralis muscle, and MMG amplitude and MPF values were computed for each corresponding percentage of the MVC. Polynomial regression analyses indicated that the composite MMG amplitude versus isometric torque relationship was best fit with a linear model (r(2) = 0.980) for the LS group and a cubic model (r(2) = 0.994) for the HS group. The composite MMG MPF versus isometric torque relationships were best fit with linear models for both the LS (r(2) = 0.529) and HS (r(2)=0.591) groups. However, only 66% of the individuals exhibited the same linear MMG amplitude patterns as the composite relationship for the LS group, whereas only 33% of the individual relationships were cubic for the HS group. Only one subject exhibited a positive linear (r(2) = 0.681) relationship for the MMG(MPF) versus isometric torque relationship for either the LS or HS groups. These findings suggested that strength differences do not affect the patterns of responses for MMG amplitude or MPF. The lack of consistency between the individual and composite patterns of responses suggested some degree of inter-individual variability. Therefore, future studies should examine the individual patterns of response to draw conclusions about motor control strategies.     

The influence of electrode shift over the innervation zone and normalization on the electromyographic amplitude and mean power frequency versus isometric torque relationships for the vastus medialis muscle

The purpose of the present study was to: (a) examine the influence of the innervation zone (IZ) for the vastus medialis on EMG signals from bipolar electrode arrangements that have their center point directly over the IZ, 10mm distal to the IZ, 10mm proximal to the IZ, and 20mm distal to the IZ, and (b) investigate the effects of normalization on EMG amplitude and center frequency values over the IZ. Ten men (mean+/-S.D. age=23.6+/-3.0 years) performed submaximal to maximal isometric muscle actions of the dominant leg extensors, and four separate bipolar surface EMG signals were detected simultaneously from the vastus medialis. One bipolar electrode arrangement had its center point located directly over the IZ, while the other electrode arrangements had their center points 10mm proximal, 10mm distal, and 20mm distal to the IZ. The results showed that there were no consistent patterns among the four electrode arrangements for the absolute and normalized EMG amplitude and mean power frequency (MPF) versus isometric torque relationships. Generally speaking, the IZ had the greatest effect on the EMG signal when the center point of the bipolar electrode arrangement was directly over it or 10mm proximal to it. In addition, normalization reduced the influence of the IZ on the absolute EMG amplitude and MPF values. Thus, these findings supported the practice of normalization, and indicated that it is a useful technique for reducing the influence of electrode location on EMG amplitude and MPF data. Future studies should examine the potential for movement of the IZ during isometric muscle actions.     

A wavelet‐based analysis of surface mechanomyographic signals from the quadriceps femoris

The purpose of this study was to use a wavelet analysis designed specifically for surface mechanomyographic (MMG) signals to examine the MMG responses of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) muscles. Fifteen healthy men [age (mean ± SD): 26.4 ± 6.1 years] volunteered to perform isometric muscle actions of the dominant leg extensors at 20%, 40%, 60%, 80%, and 100% of the maximum voluntary contraction (MVC). During each muscle action, surface MMG signals were detected from the VL, RF, and VM and processed with the MMG wavelet analysis. The results show that, for the VL and VM muscles, there was compression of the total MMG intensity spectra toward low frequencies for most force levels above 20% MVC. For the RF, however, the peak of the total MMG intensity spectrum occurred at approximately 30–40 HZ for all force levels. Because the VL, RF, and VM are all innervated by the femoral nerve, the discrepancies among the three muscles for total MMG intensity in each wavelet band may have been due to differences in architecture, muscle stiffness, and/or intramuscular pressure. Muscle Nerve 39: 355–363, 2009     

Mechanomyographic amplitude and mean power frequency responses during isometric ramp vs. step muscle actions

The purpose of the present study was to compare the mechanomyographic amplitude (MMG(RMS)) and mean power frequency (MMG(MPF)) vs. torque relationships during isometric ramp and step muscle actions for the vastus lateralis (VL) and rectus femoris (RF) muscles. Nineteen subjects (mean+/-S.D. age=24+/-4 years) performed 2 isometric maximal voluntary contractions (MVCs) before and after 2 or 3 isometric ramp muscle actions from (5-95% MVC) to 9 submaximal step muscle actions (15, 25, 35, 45, 55, 65, 75, 85, and 95% MVC). MMG signals were recorded from the VL and RF muscles, and MMG(RMS) and MMG(MPF) values were computed for each corresponding percentage of the MVC. Absolute and normalized MMG(RMS) and MMG(MPF) vs. torque relationships were analyzed and interpreted on a subject-by-subject and composite pattern basis using polynomial regression and repeated measures ANOVAs. For MMG(RMS) and MMG(MPF), only 16-53% and 11-26% of the individual responses were consistent with the composite polynomial models, respectively. In addition, the normalized composite MMG(RMS) values were greater for the RF than the VL from 35 to 85% MVC. Only 47% of the MMG(RMS) and 5% of the MMG(MPF) individual patterns of responses were the same for the ramp and step muscle actions, and differences were also observed for the composite MMG(RMS) and MMG(MPF) patterns between the ramp and step muscle actions. Overall, these findings indicated that the torque-related patterns of responses for MMG(RMS) and MMG(MPF) were different among subjects (i.e., inter-individual variability) and were muscle- (VL vs. RF) and mode-specific (ramp vs. step).