Bipolar Electrode Arrangements Research Articles

Effects of Curcumin and Fenugreek Soluble Fiber on the Physical Working Capacity at the Fatigue Threshold, Peak Oxygen Consumption, and Time to Exhaustion

Herrick, LP, Goh, J, Menke, W, Campbell, MS, Fleenor, BS, Abel, MG, and Bergstrom, HC. Effects of curcumin and fenugreek soluble fiber on the physical working capacity at the fatigue threshold, peak oxygen consumption, and time to exhaustion. J Strength Cond Res 34(12): 3346-3355, 2020-The purpose of this study was to examine the effects of curcumin in combination with fenugreek soluble fiber (CUR + FEN) or fenugreek soluble fiber alone (FEN) on the neuromuscular fatigue threshold (PWCFT), peak oxygen consumption (V˙o2peak), and time to exhaustion (Tlim) on a graded exercise test (GXT), in untrained subjects. The PWCFT estimates the highest power output that can be maintained without evidence of neuromuscular fatigue. Forty-seven untrained, college-aged subjects were randomly assigned to one of 3 supplementation groups; placebo (PLA, n = 15), CUR + FEN (500 mg·d, n = 18), or FEN (300 mg·d, n = 14). The subjects completed a maximal GXT on a cycle ergometer to determine the PWCFT, V˙o2peak, and Tlim before (PRE) and after (POST) 28 days of daily supplementation. Surface electromyographic signals were recorded from a bipolar electrode arrangement on the vastus lateralis of the right leg during each test. Separate one-way analysis of covariances were used to determine if there were between-group differences for adjusted POST-PWCFT, POST-V˙o2peak, and POST-Tlim values, covaried for the respective PRE-test scores. The adjusted POST-PWCFT for the CUR + FEN group (mean ± SD: 196 ± 58 W) was greater (p = 0.016) than the PLA group (168 ± 49 W) but the FEN group (185 ± 32 W) was not different from the CUR + FEN or PLA groups (p > 0.05). There were no differences for adjusted POST-V˙o2peak (p = 0.612) or POST-Tlim (p = 0.508) among the groups. These findings suggested curcumin combined with fenugreek soluble fiber might delay neuromuscular fatigue.

Design of a Zero‐Gap Laboratory‐Scale Polymer Electrolyte Membrane Alkaline Water Electrolysis Stack

AbstractThe development of a zero‐gap alkaline water electrolysis stack based on a heterogeneous anion‐selective polymer electrolyte membrane is reported. A bipolar electrode arrangement was selected as the most appropriate one. The design was targeted to verify the suitability of the membrane electrode assembly design and the functionality of the gas separator system developed together with the purity of the gases produced. The influence of various operational regimes on the purity of the gases was investigated. Last, but not least, a validation of the mathematical model to be used for scale‐up of the cell, foreseen for the next step of the project, was performed.

Tunable Optical Sensing with PVC-Membrane-Based Ion-Selective Bipolar Electrodes.

We show here that the response of ion-selective membrane electrodes (ISEs) based on traditional PVC membranes can be directly translated to a colorimetric readout by a closed bipolar electrode (BPE) arrangement. Because the resulting optical response is based on the turnover of the redox probe, ferroin, dissolved in a thin layer compartment, it directly indicates the potential change at the ISE in combination with a reference electrode. This class of probes measures ion activity, analogous to their ISE counterparts. Unlike other ion optodes, the response is also fully tunable over a wide concentration range by the application of an external potential and occurs in a compartment that is physically separate from the sample. To allow for the electrical charge to pass across the ion-selective electrodes, the membranes are doped with inert lipophilic electrolyte, ETH 500, but otherwise have an established composition. The observed response behavior correlates well with theory. A wide range of ion-selective membranes are confirmed to work with this readout principle, demonstrating the detection of potassium, sodium, calcium, and carbonate ions. The corresponding sigmodal calibration curve is used for quantitative analysis in a range of samples including commercial beverages and river and lake samples. The data are successfully correlated with atomic emission spectroscopy and direct potentiometry.

Can Transcranial Electrical Stimulation Localize Brain Function?

Transcranial electrical stimulation (TES) uses constant (TDCS) or alternating currents (TACS) to modulate brain activity. Most TES studies apply low-intensity currents through scalp electrodes (≤2 mA) using bipolar electrode arrangements, producing weak electrical fields in the brain (<1 V/m). Low-intensity TES has been employed in humans to induce changes in task performance during or after stimulation. In analogy to focal transcranial magnetic stimulation, TES-induced behavioral effects have often been taken as evidence for a causal involvement of the brain region underlying one of the two stimulation electrodes, often referred to as the active electrode. Here, we critically review the utility of bipolar low-intensity TES to localize human brain function. We summarize physiological substrates that constitute peripheral targets for TES and may mediate subliminal or overtly perceived peripheral stimulation during TES. We argue that peripheral co-stimulation may contribute to the behavioral effects of TES and should be controlled for by “sham” TES. We discuss biophysical properties of TES, which need to be considered, if one wishes to make realistic assumptions about which brain regions were preferentially targeted by TES. Using results from electric field calculations, we evaluate the validity of different strategies that have been used for selective spatial targeting. Finally, we comment on the challenge of adjusting the dose of TES considering dose–response relationships between the weak tissue currents and the physiological effects in targeted cortical areas. These considerations call for caution when attributing behavioral effects during or after low-intensity TES studies to a specific brain region and may facilitate the selection of best practices for future TES studies.

Treatment of oil refinery wastewater by electrocoagulation–flocculation (Case Study: Shazand Oil Refinery of Arak)

In the present study, electrocoagulation–flocculation method was used to treat the wastewater from Shazand Oil Refinery in Arak, Iran. The wastewater contained 170,000 mg/L COD and 5.3 mg/L lead (Pb). In each step of the experiment, 2 L of the refinery wastewater was poured into a pilot made up of Plexiglas, and bipolar electrode arrangement was used. Optimum values of time, pH, and voltage parameters were determined for the aluminum electrodes. Results showed that time duration of 90 m, pH of 6, and voltage of 30 V was suitable for the removal of lead and COD. It should be noted that 48% of COD was removed and lead concentration decreased from 5.3 mg/L to lower than 0.05 mg/L. In addition, the COD removal efficiencies were 56 and 64% for eight and ten aluminum electrodes, respectively. The effect of iron electrodes on the removal of COD and lead was investigated under the same optimum conditions. Comparison between iron and aluminum electrodes indicated that iron electrodes demonstrate a better efficiency by removing 66.94% of COD from wastewater. It was also found that pH played a significant role in pollutants removal due to the formation of aluminum hydroxide gelatinous polymer.

Oscillatory motion of water droplets in kerosene above co-planar electrodes in microfluidic chips

We experimentally observed oscillatory motion of water droplets in microfluidic systems with coplanar microelectrodes under imposed DC electric fields. Two-electrode arrangement with no bipolar electrode and eight-electrode arrangement with six bipolar microelectrodes were investigated. Kerosene was used as the continuous phase. We studied the dependences of the oscillation frequency on the electric field intensity and ionic strength of the water phase. We found that the electric field dependence is strongly nonlinear and discussed possible reasons of this phenomenon, e.g., the droplet deformation at electrode edges that affects the charge transfer between the electrode and droplet or the interplay between the Coulomb force on free charge and the dielectrophoretic force. Our experiments further revealed that the oscillation frequency decreases with growing salt concentration in the two-electrode arrangement, but increases in the eight-electrode arrangement, which was attributed to surface tension related processes and electrochemical processes on the bipolar electrodes. Finally, we analyzed the effects of the electric field on the oscillatory motion by means of a simplified mathematical model. It was shown that the electric force imposed on the droplet charge is the key factor to induce the oscillations and the dielectrophoretic force significantly contributes to the momentum transfer at the electrode edges. For the same electric field strength, the model is able to predict the same oscillation frequency as that observed in the experiments.

The Influence of Electrode Placement on the Physical Working Capacity At the Fatigue Threshold

PURPOSE: To examine the influence of electrode placement on the physical working capacity at the fatigue threshold (PWCFT). The PWCFT test estimates the highest power output that can be maintained without neuromuscular evidence of fatigue and is determined from the rate of increase in the amplitude of the electromyographic (EMG) signal. METHODS: Fifteen college-aged males and females (mean age ± SD = 22.6 ± 3.4 yr; BW = 74.3 ± 11.2 kg; HT = 176.1 ± 9.0 cm) performed an incremental test to exhaustion on a cycle ergometer. A linear electrode array was utilized to determine the location of the innervation zone (IZ) and muscle fiber pennation angle (MFPA) of the vastus lateralis (VL). For determination of the PWCFT values, surface EMG signals were recorded from 3 bipolar electrode arrangements at different locations over the VL during the incremental tests. The first electrode arrangement was placed on the VL at one-third of the distance between the lateral border of the patella and the anterior superior iliac spine, and oriented parallel to the MFPA. The second electrode arrangement contained the same center point as the first electrode arrangement, but was oriented parallel to the long axis of the femur. A third electrode arrangement was placed over the IZ and oriented parallel to the MFPA. RESULTS: The results of a one-way ANOVA indicated there were no significant (p < 0.05) mean differences in PWCFT values among the 3 electrode placements (parallel to the MFPA = 181 ± 40 W; parallel to the long axis of the femur = 185 ± 44 W; and over the IZ = 189 ± 54 W). In addition, there were significant correlations in PWCFT values for the electrode placement parallel to the MPFA vs. parallel to the long axis of the femur (r = 0.94) and over the IZ (r = 0.88), as well as for the electrode placement parallel to the long axis of the femur vs. over the IZ (r = 0.81). CONCLUSIONS: These findings indicated that the PWCFT test is not influenced by the placement of a bipolar electrode arrangement in relation to the MFPA or over the IZ. Practical Applications: The results of the current study suggested that the onset of neuromuscular fatigue (PWCFT) can be estimated without identification of the MFPA or IZ.

The influence of the muscle fiber pennation angle and innervation zone on the identification of neuromuscular fatigue during cycle ergometry

The purpose of the present investigation was to compare the electromyographic (EMG) responses and the estimated physical working capacity at the fatigue threshold (PWC FT) values recorded from electrode arrangements placed: (1) parallel to the muscle fiber pennation angle (MFPA), (2) parallel to the long axis of the femur, and (3) over the innervation zone (IZ) during incremental cycle ergometry. Thirteen college-aged males and females (mean age ± SD = 22.4 ± 3.4 years) performed an incremental test to exhaustion on a cycle ergometer. A linear electrode array was utilized to determine the MFPA and location of the IZ of the vastus lateralis (VL). For determination of the PWC FT values, EMG signals were recorded from three bipolar electrode arrangements at different locations over the VL. The results of a one-way repeated measures ANOVA indicated there were no significant ( p < 0.05) mean differences in PWC FT values among the electrode arrangements (parallel to the MFPA = 190 ± 36 W; parallel to the long axis of the femur = 194 ± 40 W; and over the IZ = 199 ± 51 W) or the EMG amplitude and MPF values at the common power outputs. There were also significant correlations ( r = 0.75–0.91) among the three electrode arrangements for PWC FT values. These findings suggested that the PWC FT, like absolute EMG amplitude and MPF, is robust to the influence of electrode placement over the IZ as well as the orientation with respect to the MFPA during cycle ergometry.

Effects of Arginine-Based Supplements on the Physical Working Capacity at the Fatigue Threshold

The purpose of the present study was to examine the effects of daily oral administration of arginine-based supplements for 4 weeks on the physical working capacity at the fatigue threshold (PWCFT). The PWCFT test is an electromyographic (EMG) procedure for estimating the highest power output that can be maintained without neuromuscular evidence of fatigue. The study used a double-blind, placebo-controlled design. Fifty college-aged men (mean age +/- SD = 23.9 +/- 3.0) were randomized into 1 of 3 groups: (a) placebo (n = 19); (b) 1.5 g arginine (n = 14); or (c) 3.0 g arginine (n = 17). The placebo was microcrystalline cellulose. The 1.5-g arginine group ingested 1.5 g of arginine and 300 mg of grape seed extract, whereas the 3.0 g arginine group ingested 3.0 g of arginine and 300 mg of grape seed extract. All subjects performed an incremental test to exhaustion on a cycle ergometer to determine their PWCFT before supplementation (PRE) and after 4 weeks of supplementation (POST). Surface EMG signals were recorded from the vastus lateralis using a bipolar electrode arrangement during the incremental tests for the determination of the PRE and POST supplementation PWCFT values. There were significant mean increases (PRE to POST) in PWCFT for the 1.5 g (22.4%) and 3.0 g (18.8%) supplement groups, but no change for the placebo group (-1.6%). These findings supported the use of arginine-based supplements, at the dosages examined in the present investigation, as an ergogenic aid for untrained individuals.

Electrode Shift and Normalization Reduce the Innervation Zone's Influence on EMG

The purpose of the present study was twofold: (a) to examine the influence of the innervation zone (IZ) on EMG signals from bipolar electrode arrangements that have their center point directly over the IZ, 10 mm distal to the IZ, 10 mm proximal to the IZ, and 20 mm distal to the IZ and (b) to investigate the effects of normalization on EMG amplitude and mean power frequency (MPF) values over the IZ. Ten men (mean +/- SD age = 23.6 +/- 3.0 yr) 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 lateralis. One bipolar electrode arrangement had its center point located directly over the IZ for the vastus lateralis, whereas the other electrode arrangements had their center points 10 mm proximal, 10 mm distal, and 20 mm distal to the IZ. The results showed that there were no consistent patterns among the four electrode arrangements for the absolute and the normalized EMG amplitude and MPF versus isometric torque relationships. The IZ had the greatest influence on absolute EMG amplitude and MPF values when the center point of the electrode arrangement was directly over the IZ and a decreased effect when the center point was shifted away from the IZ. In addition, normalization reduced the influence of the IZ on EMG amplitude and MPF values. Thus, these findings suggested that in situations where it is difficult to identify the precise location and/or avoid the IZ, the EMG signals can provide useful information regarding isometric torque-related changes in normalized EMG amplitude and center frequency values.

Electrode placement over the innervation zone affects the low-, not the high-frequency portion of the EMG frequency spectrum

The purpose of this study was to use a wavelet-based signal processing technique to examine the influence of electrode placement over the innervation zone (IZ) on the shape of the electromyographic (EMG) frequency spectrum. Ten healthy males (mean ± SD age = 23.6 ± 3.0 years) performed isometric muscle actions of the dominant leg extensors at 10%, 40%, 70%, and 100% of the maximum voluntary contraction (MVC). Surface EMG signals were detected simultaneously from the vastus lateralis with two bipolar electrode arrangements. One of the electrode arrangements had its center point located directly over the IZ, while the other arrangement had its center point distal to the IZ (i.e., 20 mm away). All EMG signals were processed with a wavelet-based procedure. The results showed that for all isometric torque levels, the EMG signals from the distal electrode arrangement demonstrated greater total intensity values than those for the IZ arrangement for frequencies ranging from approximately 2 to 110 Hz. There were no consistent differences, however, between the IZ and distal electrode arrangements for total EMG intensity values above 110 Hz. Thus, these findings indicated that electrode placement over the IZ affected primarily the low-, rather than the high-frequency portion of the EMG frequency spectrum.

Relationships Among Maximal Oxygen Consumption, Ventilatory Threshold, and Elactromyographic Fatigue Threshold as Performance Assessments in College Women

PURPOSE: The purpose of this study was to examine the relationships among the power outputs (W) and VO2 values (L/min) at VO2PEAK, ventilatory threshold (VT), and electromyographic fatigue threshold (EMGFT). METHODS: Thirty-seven active women (mean ± SD: 22.03 ± 3.97 years; 166.75 ± 6.73 cm; 66.51 ± 11.14 kg) volunteered to perform two cycling tests on an electronically-braked cycle ergometer. An initial incremental exercise test was performed until exhaustion (increase of 25 W every 2 min) to determine VO2PEAK and VT. Each participant also performed a discontinuous incremental cycle ergometer test to determine their EMGFT. Four, two-minute work bouts (ranging from 75-250 W) were completed starting at each participant's power output at VT and increasing 25 W each consecutive work bout. A bipolar surface electrode arrangement, placed on the vastus lateralis of the right thigh was used to record EMG amplitude, averaged over 10 s intervals during each cycling bout. The four power outputs were plotted as a function of four EMG slope coefficients, with the y-intercept defined as the EMGFT. In addition, a regression analysis was performed to predict the VO2 value at EMGFT. Two one-way repeated measures ANOVAs were used to examine differences among power output and VO2 (L/min) measures. RESULTS: For power outputs, significant differences were observed between VO2PEAK and VT (p < 0.001; r = 0.613), VT and EMGFT (p = 0.016; r = 0.682), and VO2PEAK and EMGFT (p < 0.001; r = 0.559). For VO2, significant differences were observed between VO2PEAK and VT (p < 0.001) and VO2PEAK and EMGFT (p < 0.001). The correlations among VO2PEAK and VT, VT and EMGFT, and VO2PEAK and EMGFT were r = 0.777, 0.773, and 0.737, respectively, for VO2 values. CONCLUSION: The means at which power output and VO2 occurred for VO2PEAK, VT, and EMGFT were significantly different from each other except for the VO2 values at EMGFT and VT. This similarity, in addition to the moderate correlation of 0.773, suggested that predicted VO2 at EMGFT and VT may reflect similar physiological factors involved with the onset of fatigue during incremental exercise. Therefore, suggesting that there is a close association between the onset of peripheral fatigue measured by surface EMG and the ventilatory breakpoint that is calculated from collected gases measured with open-circuit spirometry.

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, 10 mm distal to the IZ, 10 mm proximal to the IZ, and 20 mm 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 10 mm proximal, 10 mm distal, and 20 mm 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 10 mm 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.

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.

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 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.

Electromyographic instantaneous amplitude and instantaneous mean power frequency patterns across a range of motion during a concentric isokinetic muscle action of the biceps brachii

The purpose of this study was to examine the electromyographic (EMG) instantaneous amplitude (IA) and instantaneous mean power frequency (IMPF) patterns for the biceps brachii muscle across a range of motion during maximal and submaximal concentric isokinetic muscle actions of the forearm flexors. Ten adults (mean ± SD age = 22.0 ± 3.4 years) performed a maximal and a submaximal [20% peak torque (PT)] concentric isokinetic forearm flexion muscle action at a velocity of 30° s −1. The surface EMG signal was detected from the biceps brachii muscle with a bipolar electrode arrangement, and the EMG IA and IMPF versus time relationships were examined for each subject using first- and second-order polynomial regression models. The results indicated that there were no consistent patterns between subjects for EMG IA or IMPF with increases in torque across the range of motion. Some of the potential nonphysiological factors that could influence the amplitude and/or frequency contents of the surface EMG signal during a dynamic muscle action include movement of the muscle fibers and innervation zone beneath the skin surface, as well as changes in muscle fiber length and the thickness of the tissue layer between the muscle and the recording electrodes. These factors may affect the EMG IA and IMPF patterns differently for each subject, thereby increasing the difficulty of drawing any general conclusions regarding the motor control strategies that increase torque across a range of motion.

Mechanomyographic and electromyographic responses to repeated concentric muscle actions of the quadriceps femoris

In comparison to isometric muscle action models, little is known about the electromyographic (EMG) and mechanomyographic (MMG) amplitude and mean power frequency (MPF) responses to fatiguing dynamic muscle actions. Simultaneous examination of the EMG and MMG amplitude and MPF may provide additional insight with regard to the motor control strategies utilized by the superficial muscles of the quadriceps femoris during a concentric fatiguing task. Thus, the purpose of this study was to examine the EMG and MMG amplitude and MPF responses of the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) during repeated, concentric muscle actions of the dominant leg. Seventeen adults (21.8 ± 1.7 yr) performed 50 consecutive, maximal concentric muscle actions of the dominant leg extensors on a Biodex System 3 Dynamometer at velocities of 60° s −1 and 300° s −1. Bipolar surface electrode arrangements were placed over the mid portion of the VL, RF, and VM muscles with a MMG contact sensor placed adjacent to the superior EMG electrode on each muscle. Torque, MMG and EMG amplitude and MPF values were calculated for each of the 50 repetitions. All values were normalized to the value recorded during the first repetition and then averaged across all subjects. The cubic decreases in torque at 60° s −1 ( R 2 = 0.972) and 300° s −1 ( R 2 = 0.931) was associated with a decline in torque of 59 ± 24% and 53 ± 11%, respectively. The muscle and velocity specific responses for the MMG amplitude and MPF demonstrated that each of the superficial muscles of the quadriceps femoris uniquely contributed to the control of force output across the 50 repetitions. These results suggested that the MMG responses for the VL, RF, VM during a fatiguing task may be influenced by a number of factors such as fiber type differences, alterations in activation strategy including motor unit recruitment and firing rate and possibly muscle wisdom.

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 ˙ O 2 max = 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 (μV 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.