Electromyographic Mean Power Frequency Research Articles

Metabolic and neuromuscular responses at critical power from the 3-min all-out test

The purpose of this study was to determine the specific metabolic and neuromuscular responses at critical power (CP) from the 3-min all-out test. Nine men (mean ± SD: aged 23.7 ± 3.3 years) performed an incremental test for the determination of peak oxygen consumption (VO(2peak)) and gas exchange threshold. CP was estimated for each subject from the 3-min all-out test. Oxygen consumption (VO(2)), the ventilation versus carbon dioxide production ratio (V(E)/VCO(2) ratio), electromyographic (EMG) amplitude, and EMG mean power frequency (MPF) were examined during exhaustive rides at CP for each subject. There was no significant difference between the VO(2) at exhaustion (40.6 ± 7.5 mL·kg(-1)·min(-1)) and VO(2peak) (42.9 ± 7.3 mL·kg(-1)·min(-1)). Furthermore, there were significant increases in EMG amplitude and the V(E)/VCO(2) ratio during the exhaustive rides at CP. There was, however, no significant change in EMG MPF over time. Therefore, the current findings indicated that the 3-min all-out test overestimated CP and the demarcation between the heavy- and severe-intensity domains. Specifically, the VO(2), ventilatory, and EMG amplitude responses were consistent with those observed during continuous exercise in the severe exercise intensity domain. It is likely that the ventilatory and EMG amplitude responses were associated with a common mechanism of fatigue that is different from what affects EMG MPF.

Electromyographic and mechanomyographic responses across repeated maximal isometric and concentric muscle actions of the leg extensors

The purpose of the present study was to examine the patterns of responses for torque, electromyographic (EMG) amplitude, EMG mean power frequency (MPF), mechanomyographic (MMG) amplitude, and MMG MPF across 30 repeated maximal isometric (ISO) and concentric (CON) muscle actions of the leg extensors. Twelve female subjects (21.1±1.4yrs; 63.3±7.4kg) performed ISO and CON fatigue protocols with EMG and MMG signals recorded from the vastus lateralis. The relationships for torque, EMG amplitude, EMG MPF, MMG amplitude, and MMG MPF versus repetition number were examined using polynomial regression. The results indicated there were decreases (p<0.05) across the ISO muscle actions for torque (r2=0.95), EMG amplitude (R2=0.44), EMG MPF (r2=0.62), and MMG MPF (r2=0.48), but no change in MMG amplitude (r2=0.07). In addition, there were decreases across the CON muscle actions for torque (R2=0.97), EMG amplitude (R2=0.46), EMG MPF (R2=0.86), MMG amplitude (R2=0.44), and MMG MPF (R2=0.80). Thus, the current findings suggested that the mechanisms of fatigue and motor control strategies used to modulate torque production were similar between maximal ISO and CON muscle actions.

Accelerated Muscle Fatigability of Latent Myofascial Trigger Points in Humans

Muscle fatigue is prevalent in acute and chronic musculoskeletal pain conditions in which myofascial trigger points (MTPs) are involved. The aim of this study was to investigate the association of latent MTPs with muscle fatigue. Intramuscular electromyographic (EMG) recordings were obtained from latent MTPs and non-MTPs together with surface EMG recordings from the upper trapezius muscles during sustained isometric muscle contractions in 12 healthy subjects. Normalized root mean square (RMS) EMG amplitude and mean power frequency (MNF) were analyzed. The rate of perceived exertion and pain intensity from MTP side and non-MTP side were recorded. Pain intensity on the MTP side was significantly higher than the non-MTP side (P < 0.05). Intramuscular EMG from latent MTPs showed an early onset of decrease in MNF and a significant decrease at the end of fatiguing contraction as compared with non-MTPs (P < 0.05). Surface EMG from muscle fibers close to latent MTPs presented with an early onset of the increase in RMS amplitude and the increase was significantly higher than that from non-MTPs at the end of sustained isometric contraction (P < 0.05). A latent MTP is associated with an accelerated development of muscle fatigue and simultaneously overloading active motor units close to an MTP. Elimination of latent MTPs and inactivation of active MTPs may effectively reduce accelerated muscle fatigue and prevent overload spreading within a muscle.

Intersession reliability of the electromyographic signal during incremental cycle ergometry: Quadriceps Femoris

The purposes of this investigation were to determine the: (1) reproducibility of the patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF); and (2) intraclass correlation coefficient (ICC) of the EMG amplitude and MPF during three incremental cycle ergometer tests separated by 48 hours. Ten men performed incremental cycle ergometry tests to exhaustion on three separate occasions. Surface EMG signals were recorded simultaneously from the three superficial quadriceps muscles at each trial. Polynomial regression indicated that, for >95% of the cases, the best-fit model was the same at each trial for EMG amplitude but not for EMG MPF. The ICC values were high for EMG amplitude but low for EMG MPF. These results indicate that EMG amplitude is a reliable measure of motor unit activation strategy during incremental cycle ergometry, whereas the EMG MPF was unreliable.

Effects of local elastic compression on muscle strength, electromyographic, and mechanomyographic responses in the lower extremity

The purpose of this study was to investigate the effect of elastic compression on muscle strength, electromyographic (EMG), and mechanomyographic (MMG) responses of quadriceps femoris during isometric and isokinetic contractions. Twelve participants performed 5 s isometric maximal voluntary contractions (MVC) and 25 consecutive and maximal isokinetic knee extensions at 60 and 300 °/s with no (control, CC), medium (MC), and high (HC) compression applied to the muscle. The EMG and MMG signals were collected simultaneously with muscle isometric and isokinetic strength data. The results showed that the elevated compression did not improve peak torque, peak power, average power, total work, and regression of torque in the isometric and isokinetic contractions. However, the root mean squared value of EMG in both HC and MC significantly decreased compared with CC at 60 and 300 °/s ( p < 0.01). Furthermore, the EMG mean power frequency in HC was significantly higher than that in CC at 60 °/s ( p < 0.05) whereas no significant compression effect was found in the MMG mean power frequency. These findings provide preliminary evidence suggesting that the increase in local compression pressure may effectively increase muscle efficiency and this might be beneficial in reducing muscle fatigue during concentric isokinetic muscle contractions.

The Relationship Between Skinfold Thickness and the Amplitude and Frequency Domains of the Surface Electromyographic Signal During Cycle Ergometry

It has been suggested that the thickness of the subcutaneous tissue layer affects time and frequency domain parameters of the surface electromyography (EMG) signal. PURPOSE: The purpose of the present study was to examine the effects of skinfold thickness on the amplitude and mean power frequency (MPF) of the EMG signal from the vastus lateralis (VL) muscle during cycle ergometry. METHODS: Twenty adults (13 men and 7 women; mean age ± SD = 23.8 ± 3.0 yr) volunteered for this study. A bipolar surface EMG electrode configuration (30 mm center-to-center distance) was placed over the vastus lateralis (VL) muscle at one-third of the distance from the lateral border of the patella to the anterior superior iliac spine. EMG amplitude and MPF values were measured during incremental cycle ergometry at 50, 75, 100, 125, and 175 W. The incremental cycle ergometry test began at 50 W and increased by 25 W every 2 min. In addition, three skinfold measurements (mm) were taken from the VL at the site of the EMG electrode placement with the average value used in subsequent analyses. Simple linear regression was used to determine the relationships for EMG amplitude and MPF versus skinfold thickness at each power output. In addition, independent t-tests were used to compare the mean values for EMG amplitude and MPF between the 10 subjects with the largest skinfold values (mean ± SD = 16.7 ± 5.2 mm) and those (n = 10) with the smallest skinfold values (mean ± SD = 6.6 ± 1.2 mm). RESULTS: The simple linear regression analyses revealed no significant (p > 0.05) correlations between skinfold thickness and EMG amplitude (r = 0. 18 – 0.40) or MPF (r = 0. 17 – 0.41) at any of the power outputs. Furthermore, there were no significant mean differences (p > 0.05) in EMG amplitude or MPF between the subjects with the largest skinfold values and those with the smallest skinfold values. CONCLUSIONS: The results of the present study indicated that skinfold thickness did not affect absolute values for EMG amplitude or MPF from the VL muscle during cycle ergometry at five power outputs. These findings suggest that there maybe differences between the results of simulation studies and measured findings from surface EMG studies. PRACTICAL APPLICATIONS: Subcutaneous tissue thickness is just one of many possible factors that can affect the amplitude and frequency domains of the EMG signal. Other factors include the conductivities of the tissue, interelectrode distance, and the number of recruited motor units. The current findings provide information regarding a methodological consideration associated with the application of surface EMG measurements.

Comparing electromyographic and mechanomyographic frequency-based fatigue thresholds to critical torque during isometric forearm flexion

Theoretically, the critical torque (CT), electromyographic mean power frequency fatigue threshold (EMG MPF FT), and mechanomyographic mean power frequency fatigue threshold (MMG MPF FT) describe the maximal non-fatiguing isometric torque level. Purpose The purposes of this study were threefold: (1) to determine if the mathematical model for estimating the EMG MPF FT during isometric muscle actions of the leg extensors was applicable to isometric muscle actions of the forearm flexors; (2) to determine if the mathematical model for estimating the EMG MPF FT from the frequency of the EMG signal was applicable to the frequency domain of the MMG signal to estimate a new fatigue threshold called the mechanomyographic mean power frequency fatigue threshold (MMG MPF FT); and (3) to compare the mean torque levels derived from the CT, EMG MPF FT, and MMG MPF FT tests during isometric forearm flexion muscle actions. Methods Ten adults (4 men and 6 women, mean ± SD; age = 22.0 ± 2.1 years) performed three or four continuous, fatiguing, isometric muscle actions of the forearm flexors at 30, 45, 60, and 75% of maximum voluntary isometric contraction (MVIC) to determine the time to exhaustion ( T lim) values. The slope coefficient of the linear relationship between total isometric “work” ( W lim in N m s = torque × T lim) and T lim was defined as the CT. Surface EMG and MMG signals were recorded from the biceps brachii muscle during each fatiguing isometric muscle action. The EMG and MMG MPF FT were defined as the y-intercepts of the isometric torque versus slope coefficient (EMG and MMG MPF versus time) plots. Results There were no significant differences between fatigue thresholds (CT = 26.3 ± 0.8, EMG MPF FT = 31.4 ± 4.2, and MMG MPF FT = 29.5 ± 7.0%MVIC), and the mean torque values (N m) from the three fatigue thresholds were significantly intercorrelated at r = 0.94–0.96. Conclusion The EMG MPF FT test may provide a non-invasive method to examine the effects of interventions on the conduction velocity and shape of the action potential waveform. In addition, the effects of interventions on the global motor unit firing rate of the unfused, activated motor units may be examined by the non-invasive methods of the MMG MPF FT test.

Fatigue‐related changes in fascicle–tendon geometry over repeated contractions: Difference between synergist muscles

Fatigue-induced changes in force production of synergist muscles were evaluated through observation of fascicle-tendon geometry and electromyography (EMG). Seven subjects performed 60 maximal isometric plantar flexions intermittently. No statistically significant intermuscle difference was observed in the decrease of mean EMG amplitudes or mean power frequency for the medial gastrocnemius (MG) and soleus (SOL) muscles. The tendon elongation of MG significantly decreased after the 19th contraction, and MG fascicle length increased after the 29th contraction, while SOL fascicle and tendon length did not change except for the last contraction. The declines in torques were highly correlated with the increase of MG fascicle length and decrease in tendon elongation in each subject, while no consistent relationship was found for SOL. These results suggest that changes in force-production of MG and SOL over repeated contractions differ, which is reflected in fascicle-tendon geometry.

Neuromuscular fatigue following low-intensity dynamic exercise with externally applied vascular restriction

This study investigated neuromuscular fatigue following low-intensity resistance exercise with vascular restriction (VR) and without vascular restriction (control, CON). Fourteen males participated in two experimental trials (VR and CON) each separated by 48 h. Each participant performed two isometric maximum voluntary contractions (MVCs) before and after five sets of 20 dynamic constant external resistance leg extension exercises (DCER-EX) at 20% of one-repetition maximum (1-RM). The participants were asked to lift (1.5 s) and lower (1.5 s) the load at a constant velocity. Surface electromyography (EMG) was recorded from the vastus lateralis during MVC and DCER-EX. Twitch interpolation was used to assess the percent of maximal voluntary activation (%VA) during the MVC. During performing five sets of 20 DCER-EX, the increases ( p < 0.05) in EMG amplitude and decreases ( p < 0.05) in EMG mean power frequency were similar for both VR and CON. However, there were significant differences between VR and CON for MVC force, %VA, and potentiated twitch force and significant interactions for EMG amplitude. VR decreased MVC force, %VA, potentiated twitch force, and EMG amplitude more than CON. Our findings suggest that the VR-induced fatigue may have been due to a combination of peripheral (decreases in potentiated twitch) and central (decreases in %VA and EMG amplitude) fatigue.

The Effects Of Parallel Versus Perpendicular Electrode Orientations On EMG Amplitude And Mean Power Frequency From The Biceps Brachii

PURPOSE: The purpose of this study was to examine the influence of electrode orientation on the electromyographic (EMG) amplitude and mean power frequency (MPF) versus isometric torque relationships for the biceps brachii muscle. METHODS: Ten adults [five men (mean ± SD age = 23.8 ± 2.8 years) and five women (mean ± SD age = 23.8 ± 2.2 years)] volunteered to participate in the investigation. Two separate bipolar surface EMG electrode arrangements (20 mm center to center) were placed on the dominant arm over the biceps brachii muscle. One EMG arrangement was placed parallel and the other perpendicular to the direction of the muscle fibers of the biceps brachii. The subjects performed two maximal, 6-second isometric muscle actions at a forearm flexion angle of 60° above the horizontal plane to determine maximal voluntary isometric contraction (MVIC). The subjects then performed a series of randomly ordered submaximal muscle actions in 10% increments from 10 to 90% MVIC. Paired t-test were used to examine mean differences between the two electrode orientations for absolute and normalized EMG amplitude and MPF values at each torque levels. RESULTS: The mean 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, there were no significant (p > 0.05) mean differences between the parallel and perpendicular EMG electrode orientations for any of the %MVIC values. Furthermore, there were no significant mean differences between the parallel and perpendicular EMG electrode orientations for absolute or normalized EMG MPF for any of the %MVIC values. CONCLUSIONS: These findings indicated that, unlike absolute EMG amplitude, normalized EMG amplitude values were not affected by electrode orientation. Thus, normalization can be used to reduce the effects of electrode orientation on EMG amplitude during isometric muscle actions of the biceps brachii. Furthermore, electrode orientation had no effect on absolute or normalized EMG MPF.

A new EMG frequency-based fatigue threshold test

Theoretically, the critical torque (CT) and electromyographic mean power frequency fatigue threshold (EMG MPFFT) describe the maximal non-fatiguing isometric torque level. PurposeThe purposes of this study were two-fold: (1) to determine if the mathematical model for estimating the EMG fatigue threshold (EMGFT) from the amplitude of the EMG signal was applicable to the frequency domain of the EMG signal to estimate a new fatigue threshold called the EMG MPFFT; and (2) to compare the torque level derived from the CT test to that of the EMG MPFFT test for the vastus lateralis (VL) muscle during isometric muscle actions of the leg extensors. MethodsNine adults (4 men and 5 women; mean±SD age=21.6±1.2yr) performed three or four continuous, fatiguing, isometric muscle actions of the leg extensors at 30, 45, 60, and 75% of maximum voluntary isometric contraction (MVIC) to determine the time to exhaustion (Tlim) values. The slope coefficient of the linear relationship between total isometric “work” (Wlim in Nms=Torque×Tlim) and Tlim was defined as the CT. Surface EMG signals were recorded from the vastus lateralis (VL) muscle during each fatiguing isometric muscle action. The EMG MPFFT was defined as the y-intercept of the isometric torque versus slope coefficient (EMG MPF versus time) plot. ResultsThere were no significant differences between CT (19.7±5.8%MVIC) and EMG MPFFT (21.4±8.7%MVIC). ConclusionThese findings provided indirect validation of the EMG MPFFT test.

Comparison of electromyographic responses for the superficial quadriceps muscles: Cycle versus knee-extensor ergometry

The purpose of this study was to compare the electromyographic (EMG) amplitude and mean power frequency (MPF) versus power output relationships for the three superficial quadriceps muscles during incremental cycle (CE) and knee-extensor (KE) ergometry in the same subjects. Eight men performed incremental CE and KE tests to exhaustion. Surface EMG signals were recorded simultaneously from the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM). Polynomial regression analyses on a subject-by-subject basis indicated that the relationship between EMG amplitude versus power output was best-fit with either a linear, quadratic, or cubic model for CE, whereas the relationship was best-fit with a linear model for all subjects for the KE test. No consistent relationship was found for EMG MPF within subjects and between muscle groups for CE or KE. Compared with CE, however, the EMG amplitude during KE exercise was, on average, approximately 87% and 30% higher for the RF and VM muscles, respectively. These results suggest that KE exercise may be a better mode of examining EMG amplitude in the quadriceps muscle during incremental exercise than traditional CE.

Low-level activity of the trunk extensor muscles causes electromyographic manifestations of fatigue in absence of decreased oxygenation

This study was designed to determine whether trunk extensor fatigue occurs during low-level activity and whether this is associated with a drop in muscle tissue oxygenation. Electromyography (EMG) feedback was used to impose constant activity in a part of the trunk extensor muscles. We hypothesized that electromyographic manifestations of fatigue and decreased oxygenation would be observed at the feedback site and that EMG activity at other sites would be more variable without fatigue manifestations. Twelve volunteers performed 30-min contractions at 2% and 5% of the maximum EMG amplitude (EMGmax) at the feedback site. EMG was recorded from six sites over the lumbar extensor muscles and near-infrared spectroscopy was used to measure changes in oxygenation at the feedback site (left L3 level, 3 cm paravertebral). In both conditions, mean EMG activity was not significantly different between electrode sites, whereas the coefficient of variation was lower at the feedback site compared to other recording sites. The EMG mean power frequency (MPF) decreased consistently at the feedback site only. At 5% EMGmax, the decrease in MPF was significant at the group level at all sites ipsilateral to the feedback site. These results suggest that the limited variability of muscle activity at the EMG feedback site and at ipsilateral locations enhances fatigue development. No decreases in tissue oxygenation were detected. In conclusion, even at mean activity levels as low as 2% EMGmax, fatigue manifestations were found in the trunk extensors. These occured in absence of changes in oxygenation of the muscle tissue.

The effects of interelectrode distance over the innervation zone and normalization on the electromyographic amplitude and mean power frequency versus concentric, eccentric, and isometric torque relationships for the vastus lateralis muscle

The purpose of this study was to examine the influence of interelectrode distance (IED) over the estimated innervation zone (IZ) for the vastus lateralis muscle and normalization on the torque-related patterns of responses for electromyographic (EMG) amplitude and mean power frequency (MPF) during concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the leg extensors. Eight men performed submaximal to maximal concentric isokinetic, eccentric isokinetic, and isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously with two bipolar electrode arrangements in single differential configuration (20 and 40 mm IEDs) placed over the estimated IZ for the vastus lateralis muscle and a third electrode arrangement in single differential configuration (20 mm IED) placed distal to the estimated IZ. The results indicated that there were only a few (six of 90 statistical comparisons) significant ( p < 0.05) mean differences among the three electrode arrangements for absolute EMG amplitude. There were no mean differences among the three electrode arrangements for absolute or normalized EMG MPF values or normalized EMG amplitude for the three types of muscle actions. Thus, it may be possible to reduce the potential influence of the IZ on amplitude and spectral parameters of the EMG signal through normalization.

The Effect of the Estimated Innervation Zone on EMG Amplitude and Center Frequency

The purpose of this study 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 isometric torque-related patterns for electromyographic (EMG) amplitude and mean power frequency (MPF). Eleven men performed submaximal to maximal isometric muscle actions of the dominant leg extensors. Surface EMG signals were recorded simultaneously from the vastus lateralis muscle with bipolar electrode arrangements placed over the estimated IZ, as well as proximally and distally to the estimated IZ. The results indicate that the patterns of response and mean values for absolute and normalized EMG amplitude and MPF versus isometric torque over the estimated IZ were not consistently different from those away from the IZ. There were, however, mean differences among electrode-placement sites for absolute EMG amplitude values (distal site > proximal and/or estimated IZ sites by approximately 76 microVrms) that were not eliminated with normalization (proximal site > distal and/or estimated IZ sites by approximately 5% max). Although these differences were not attributable to the IZ, they suggest that during isometric muscle actions, normalized EMG amplitude values from different individuals cannot be compared if the EMG signals are detected from different electrode locations over the muscle of interest.

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.

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.

The effects of electrode placement and innervation zone location on the electromyographic amplitude and mean power frequency versus isometric torque relationships for the vastus lateralis muscle

The purposes of this investigation were to examine the effects of electrode placement and innervation zone (IZ) location on: (a) the torque-related patterns of responses for absolute and normalized electromyographic (EMG) amplitude and mean power frequency (MPF) and (b) the mean absolute and normalized EMG amplitude and MPF values. In addition, the present study examined the variability between subjects for the location of the IZ for the vastus lateralis (VL). Eight men (mean ± SD age = 23.0 ± 4.3 yr) performed submaximal to maximal isometric muscle actions of the dominant leg extensors. During each muscle action, fifteen channels of bipolar surface EMG signals were detected from the vastus lateralis using a linear electrode array aligned with the long axis of the muscle fibers. The results indicated that there were differences among channels 1–15 for the patterns of responses and mean values for absolute and normalized EMG amplitude and MPF versus isometric torque. Thus, normalized EMG amplitude and MPF values from different individuals cannot be compared if the EMG signals were detected from different locations over the muscle. In addition, absolute and relative (to femur length) estimates of IZ location for the VL resulted in similar inter-subject variability.

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; V ˙ O 2 max = 47.3 ± 4.9 ml k g − 1 mi n − 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 (μVrms 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.

Neuromuscular Responses to Three Days of Velocity-Specific Isokinetic Training

The purpose of this investigation was to examine the effects of 3 days of velocity-specific isokinetic training on peak torque (PT) and the electromyographic (EMG) signal. Thirty adult women were randomly assigned to a slow-velocity training (SVT), fast-velocity training (FVT), or control (CON) group. All subjects performed maximal, concentric, isokinetic leg extension muscle actions at 30 and 270 degrees .s(-1) for the determination of PT on visits 1 (pretest) and 5 (posttest). Electromyographic signals were recorded from the vastus lateralis, rectus femoris, and vastus medialis muscles during each test. The training groups performed 4 sets of 10 maximal repetitions at 30 degrees .s(-1) (SVT group) or 270 degrees .s(-1) (FVT group) on visits 2, 3, and 4. For the SVT group, PT increased from pretest to posttest at 30 and 270 degrees .s(-1). The increase in PT at 30 degrees .s(-1) was greater than at 270 degrees .s(-1). For the FVT group, PT increased at 270 degrees .s(-1) only. For the CON group, there were no changes in PT at either velocity. There were no pretest to posttest changes in EMG amplitude or mean power frequency (MPF) for any group at any velocity, with the exception of an increase in EMG MPF from the vastus medialis muscle at 270 degrees .s(-1) for the FVT group. The results indicated that 3 sessions of slow velocity (30 degrees .s(-1)) isokinetic training resulted in an increase in PT at slow and fast velocities (30 and 270 degrees .s(-1)), whereas training at the fast velocity (270 degrees .s(-1)) increased PT only at 270 degrees .s(-1). The lack of consistent increases in EMG amplitude or MPF suggested that the training-induced increases in leg extension PT were not caused by increased activation of the superficial muscles of the quadriceps femoris. The important implication for coaches, trainers, and physical therapists is that significant muscular performance gains may be achieved even after very short training periods, but determination of the specific physiological adaptation(s) underlying these performance gains requires further investigation.