The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Clayton L. Camic - One of the best experts on this subject based on the ideXlab platform.
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Validation of the physical working capacity at the Fatigue Threshold treadmill test
Kinesiology, 2017Co-Authors: Clayton L. Camic, Chelsea J. Hahn, Benjamin C. Hendrickson, Andrew R. JagimAbstract:The purposes of the present study were twofold: 1) to determine the physical working capacity at the Fatigue Threshold (PWCFT) during an incremental treadmill test, and 2) to examine the validity of this Fatigue Threshold through constant-velocity runs to exhaustion at 90, 100, and 110% of the estimated PWCFT. Twelve aerobically-trained males (mean age±SD=24.6±5.4 years, running volume=69.9±46.0 km·wk-1, n=9) and females (22.3±2.3 years, 45.6±4.6 km·wk-1, n=3) volunteered to perform a treadmill test to exhaustion with electromyographic (EMG) signals recorded from the m. vastus lateralis on four separate visits. The First visit required each subject to complete an incremental treadmill test to exhaustion for determination of their PWCFT. During the second, third, and fourth visit, the subjects completed a treadmill run to exhaustion at a constant velocity that corresponded to 90, 100, or 110% of their PWCFT in random order. The linear regression analyses indicated there were no significant (p>.05) changes in muscle activation (i.e. EMG amplitude) across time to exhaustion during the constant velocity runs at 90% (60.00±0.00 min) and 100% (48.86±14.59 min) PWCFT, but significant (p
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A mechanomyographic Fatigue Threshold test for cycling.
International journal of sports medicine, 2010Co-Authors: Jorge M. Zuniga, Clayton L. Camic, Terry J. Housh, Michelle Mielke, Richard J. Schmidt, C. R. Hendrix, Glen O. JohnsonAbstract:The purposes of this study were twofold: 1) to derive the mechanomyographic mean power frequency Fatigue Threshold (MMG MPF FT ) for submaximal cycle ergometry; and 2) to compare the power outputs associated to the MMG MPF FT to other neuromuscular and gas exchange Fatigue Thresholds. 9 adults (5 men and 4 women; mean±SD age=23.7±3.7 years; body weight = 66.3 ± 8.2 kg) performed an incremental cycle ergometry test to exhaustion while expired gas samples, electromyographic (EMG), and MMG signals were measured from the vastus lateralis muscle. The non-significant correlations (r=0.17 to 0.66; p>0.05) among the physical working capacity at the Fatigue Threshold (PWC FT ), MMG MPF FT , and gas exchange Threshold (GET) suggested that different physiological mechanisms may underlie these 3 Fatigue Thresholds. A significant correlation (r=0.83) for the MPF FT vs. respiratory compensation point (RCP) suggested that these Fatigue Thresholds may be mediated by a common physiological mechanism. In addition, the significantly lower mean values found for the PWC FT (mean ± SD = 163 ± 43 W), MMG MPF FT (132±33 W), and GET (144±28 W) than MPF FT (196±53 W) and RCP (202±41 W) suggested that these gas exchange and neuromuscular Fatigue Thresholds may demarcate different exercise intensity domains.
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effects of arginine based supplements on the physical working capacity at the Fatigue Threshold
Journal of Strength and Conditioning Research, 2010Co-Authors: Clayton L. Camic, Terry J. Housh, Glen O. Johnson, Michelle Mielke, Jorge M. Zuniga, Russell Hendrix, Richard J. SchmidtAbstract: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.
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an emg frequency based test for estimating the neuromuscular Fatigue Threshold during cycle ergometry
European Journal of Applied Physiology, 2010Co-Authors: Clayton L. Camic, Terry J. Housh, Glen O. Johnson, Michelle Mielke, Jorge M. Zuniga, Russell C Hendrix, Richard J. SchmidtAbstract:The purposes of this investigation were twofold: (1) to determine if the model used for estimating the physical working capacity at the Fatigue Threshold (PWCFT) from electromyographic (EMG) amplitude data could be applied to the frequency domain of the signal to derive a new Fatigue Threshold for cycle ergometry called the mean power frequency Fatigue Threshold (MPFFT), and (2) to compare the power outputs associated with the PWCFT, MPFFT, ventilatory Threshold (VT), and respiratory compensation point (RCP). Sixteen men [mean (SD) age = 23.4 (3.2) years] performed incremental cycle ergometer rides to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis. There were significant (p < 0.05) mean differences for PWCFT [mean (SD) = 168 (36) W] versus MPFFT [208 (37) W] and VT [152 (33) W] versus RCP [205 (84) W], but no mean differences for PWCFT versus VT or MPFFT versus RCP. The mean difference between PWCFT and MPFFT may be due to the effects of specific metabolites that independently influence the time and frequency domains of the EMG signal. These findings indicated that the PWCFT model could be applied to the frequency domain of the EMG signal to estimate MPFFT. Furthermore, the current findings suggested that the PWCFT may demarcate the moderate from heavy exercise domains, while the MPFFT demarcates heavy from severe exercise intensities.
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A mechanomyographic frequency-based Fatigue Threshold test.
Journal of neuroscience methods, 2009Co-Authors: C. Russell Hendrix, Clayton L. Camic, Terry J. Housh, Glen O. Johnson, Michelle Mielke, Jorge M. Zuniga, Richard J. SchmidtAbstract:A B 5 T R ACT Theoretically, the mechanomyographic (MMG) mean power frequency Fatigue Threshold (MMGMPFFf ) describes the maximal isometric torque that can be maintained for an extended period of time with no change in the global firing rate of the unfused, activated motor units. Purpose: The purposes of this study were twofold: (1) to determine if the mathematical model for esti mating the electromyographic (EMG) MPFFf 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 MMG MPF Ff : and (2) to compare the mean torque levels derived from the MMG MPF Ff test for the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles during isometric leg extension muscle actions. Methods: Nine adults (4 men and 5 women: mean ±S.D. age = 21.6 ± 1.2 years) 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 exhaustion. Surface MMG signals were recorded from the VL, VM,and RF muscles during each fatiguing isometric muscle action. The MMG MPFFf was defined as the y-intercept of the isometric torque versus slope coefficient (MMGMPF versus time) plot. Results: There were no significant differences among the MMG MPFFf values for the VL, VM, and RF
Jamie J. Kruzic - One of the best experts on this subject based on the ideXlab platform.
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Fatigue Threshold R‐curves Predict Fatigue Endurance Strength for Self‐Reinforced Silicon Nitride
Journal of the American Ceramic Society, 2013Co-Authors: Rawley B. Greene, Stefan Fünfschilling, Theo Fett, Michael J. Hoffmann, Jamie J. KruzicAbstract:There is a need for methods that can help predict and avoid Fatigue failures of silicon nitride ceramic components. The Fatigue Threshold R-curve has been proposed as potential solution to this problem. In this study, the Fatigue Threshold R-curve for small, semielliptical surface cracks was calculated for a silicon nitride ceramic using the published bridging stress distribution developed from Fatigue Threshold tests on macroscopic crack specimens. To test the accuracy of the endurance strengths predicted using the Fatigue Threshold R-curve, Fatigue tests were conducted using four-point bend beams of silicon nitride containing semielliptical surface cracks introduced by Knoop indentation. The effectiveness of the methodology was verified; indeed, 77% of the beams tested at stress levels above the predicted endurance strength failed within 107 cycles and 0% of the beams tested below the predicted endurance strength failed within 107 cycles. Furthermore, using the bridging stress distribution, which is thought to be a material property, the need for prohibitively difficult Fatigue Threshold experiments on small surface cracks is avoided. Accordingly, this methodology is potentially quite practical for use in the engineering design of ceramic mechanical components.
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Fatigue Threshold r curve behavior of grain bridging ceramics role of grain size and grain boundary adhesion
Journal of the American Ceramic Society, 2011Co-Authors: Sarah Gallops, Theo Fett, Jamie J. KruzicAbstract:To better understand the role of grain size and grain-boundary adhesion on the Fatigue Threshold R-curve behavior of grain bridging ceramics, a study was conducted on the Fatigue Threshold behavior of 99.5% pure polycrystalline alumina with two different microstructures (fine and coarse) and in two different environments (moist air and dry N2). The fine-grained microstructure showed higher Fatigue Thresholds at short crack sizes, while the coarse-grained microstructure demonstrated higher Fatigue Thresholds at long crack sizes. The former effect lead to slightly higher calculated Fatigue strengths and was attributed to the crack stalling process that leads to earlier elastic bridge formation in that microstructure. The latter effect is attributed to toughening that is dominated by frictional and mechanical interlocking bridges at longer crack sizes where the larger grains are able to give more bridging. By testing the coarse microstructure in a dry environment, a higher K0 was achieved for the glassy grain boundaries giving a higher R-curve at short crack sizes and higher calculated Fatigue strengths.
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Fatigue Threshold R‐Curve Behavior of Grain Bridging Ceramics: Role of Grain Size and Grain‐Boundary Adhesion
Journal of the American Ceramic Society, 2011Co-Authors: Sarah Gallops, Theo Fett, Jamie J. KruzicAbstract:To better understand the role of grain size and grain-boundary adhesion on the Fatigue Threshold R-curve behavior of grain bridging ceramics, a study was conducted on the Fatigue Threshold behavior of 99.5% pure polycrystalline alumina with two different microstructures (fine and coarse) and in two different environments (moist air and dry N2). The fine-grained microstructure showed higher Fatigue Thresholds at short crack sizes, while the coarse-grained microstructure demonstrated higher Fatigue Thresholds at long crack sizes. The former effect lead to slightly higher calculated Fatigue strengths and was attributed to the crack stalling process that leads to earlier elastic bridge formation in that microstructure. The latter effect is attributed to toughening that is dominated by frictional and mechanical interlocking bridges at longer crack sizes where the larger grains are able to give more bridging. By testing the coarse microstructure in a dry environment, a higher K0 was achieved for the glassy grain boundaries giving a higher R-curve at short crack sizes and higher calculated Fatigue strengths.
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Fatigue Threshold R-curves predict small crack Fatigue behavior of bridging toughened materials
Acta Materialia, 2011Co-Authors: S. Gallops, Theo Fett, Joel W. Ager, Jamie J. KruzicAbstract:Abstract Small crack Fatigue is a widely recognized problem in the Fatigue of materials; however, there has been limited progress in developing methods to predict small crack Fatigue behavior. In this paper small crack effects due to crack bridging are addressed. A Fatigue Threshold R -curve was measured for a 99.5% pure polycrystalline alumina using standard compact tension specimens and was used (i) to determine the bridging stress profile for the material and (ii) to make Fatigue endurance strength predictions for realistic semi-elliptical surface cracks. Furthermore, it has been shown that the Fatigue Threshold R -curve can equivalently be determined by measuring the bridging stress distribution, in this case using fluorescence spectroscopy, using only a long crack compact tension specimen without the need for difficult small crack experiments. It is expected that this method will be applicable to a wide range of bridging toughened materials, including composites, toughened ceramics, intermetallics, and multi-phase materials.
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Fatigue Threshold r curves for predicting reliability of ceramics under cyclic loading
Acta Materialia, 2005Co-Authors: Jamie J. Kruzic, R M Cannon, J W Ager, R O RitchieAbstract:Abstract For monolithic, grain-bridging ceramics, the crack-size dependence of the Fatigue Threshold during bridging zone development presents a difficulty in its application in design. This paper demonstrates how a Fatigue Threshold R -curve may express this crack-size dependence, analogous to the traditional fracture toughness R -curve, and may be used to predict the endurance limit and retained strength under cyclic loading conditions. Furthermore, the Fatigue Threshold R -curve may be deduced from the behavior of millimeter-scale, through-thickness, Fatigue cracks via an accurately measured crack bridging stress profile. Both an alumina ceramic with large steady-state bridging zones (∼2 mm), where the predicted and experimentally measured Fatigue Threshold R -curves agree well over a range of crack sizes from 0.06 to 7 mm, and a (Y 2 O 3 -MgO)-doped Si 3 N 4 ceramic, where bridging zones are much shorter (∼100 μm), are investigated. The approach provides a useful alternative to performing difficult short-crack Fatigue experiments, particularly for materials with small bridging zones.
Christian Froyd - One of the best experts on this subject based on the ideXlab platform.
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no critical peripheral Fatigue Threshold during intermittent isometric time to task failure test with the knee extensors
Frontiers in Physiology, 2016Co-Authors: Christian Froyd, Fernando G Beltrami, Guillaume Y Millet, Timothy D NoakesAbstract:It has been proposed that group III and IV muscle afferents provide inhibitory feedback from locomotor muscles to the central nervous system, setting an absolute Threshold for the development of peripheral Fatigue during exercise. The aim of this study was to test the validity of this theory. Thus, we asked whether the level of developed peripheral Fatigue would differ when two consecutive exercise trials were completed to task failure. Ten trained sport students performed two exercise trials to task failure on an isometric dynamometer, allowing peripheral Fatigue to be assessed 2 s after maximal voluntary contraction (MVC) post task failure. The trials, separated by 8 min, consisted of repeated sets of 10 × 5-s isometric knee extension followed by 5-s rest between contractions. In each set, the first nine contractions were performed at a target force at 60% of the pre-exercise MVC, while the 10th contraction was a MVC. MVC and evoked force responses to supramaximal electrical femoral nerve stimulation on relaxed muscles were assessed during the trials and at task failure. Stimulations at task failure consisted of single stimulus (SS), paired stimuli at 10 Hz (PS10), paired stimuli at 100 Hz (PS100), and 50 stimuli at 100 Hz (tetanus). Time to task failure for the first trial (12.84 ± 5.60 min) was longer (P < 0.001) than for the second (5.74 ± 1.77 min). MVC force was significantly lower at task failure for both trials compared with the pre-exercise values (both P < 0.001), but there were no differences in MVC at task failure in the first and second trials (P = 1.00). However, evoked peak force for SS, PS100, and tetanus were all reduced more at task failure in the second compared to the first trial (P = 0.014 for SS, P < 0.001 for PS100 and tetanus). These results demonstrate that subjects do not terminate exercise at task failure because they have reached a critical Threshold in peripheral Fatigue. The present data therefore question the existence of a critical peripheral Fatigue Threshold during intermittent isometric exercise to task failure with the knee extensors.
Samuel Kwofie - One of the best experts on this subject based on the ideXlab platform.
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equivalent stress approach to predicting the effect of stress ratio on Fatigue Threshold stress intensity range
International Journal of Fatigue, 2004Co-Authors: Samuel KwofieAbstract:Abstract A previously proposed exponential stress function for predicting the effect of mean stress on Fatigue life of smooth specimens is employed to account for the effect of stress ratio on the Fatigue stress intensity range for crack-like members. By means of equivalent stress that is expected to yield the same damaging effect as combined cyclic and mean stresses, a relation between Fatigue Threshold stress intensity range Δ K th and stress ratio R is derived. It is indicated that the R -sensitivity on Δ K th is controlled by a single parameter, which appears to depend on the degree of crack closure exhibited by the material under the loading conditions. Predictions of the relation are compared with published experimental data and agreement is found to be very good. The R -effect on Δ K th is briefly discussed in terms of crack closure.
Richard J. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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A mechanomyographic Fatigue Threshold test for cycling.
International journal of sports medicine, 2010Co-Authors: Jorge M. Zuniga, Clayton L. Camic, Terry J. Housh, Michelle Mielke, Richard J. Schmidt, C. R. Hendrix, Glen O. JohnsonAbstract:The purposes of this study were twofold: 1) to derive the mechanomyographic mean power frequency Fatigue Threshold (MMG MPF FT ) for submaximal cycle ergometry; and 2) to compare the power outputs associated to the MMG MPF FT to other neuromuscular and gas exchange Fatigue Thresholds. 9 adults (5 men and 4 women; mean±SD age=23.7±3.7 years; body weight = 66.3 ± 8.2 kg) performed an incremental cycle ergometry test to exhaustion while expired gas samples, electromyographic (EMG), and MMG signals were measured from the vastus lateralis muscle. The non-significant correlations (r=0.17 to 0.66; p>0.05) among the physical working capacity at the Fatigue Threshold (PWC FT ), MMG MPF FT , and gas exchange Threshold (GET) suggested that different physiological mechanisms may underlie these 3 Fatigue Thresholds. A significant correlation (r=0.83) for the MPF FT vs. respiratory compensation point (RCP) suggested that these Fatigue Thresholds may be mediated by a common physiological mechanism. In addition, the significantly lower mean values found for the PWC FT (mean ± SD = 163 ± 43 W), MMG MPF FT (132±33 W), and GET (144±28 W) than MPF FT (196±53 W) and RCP (202±41 W) suggested that these gas exchange and neuromuscular Fatigue Thresholds may demarcate different exercise intensity domains.
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effects of arginine based supplements on the physical working capacity at the Fatigue Threshold
Journal of Strength and Conditioning Research, 2010Co-Authors: Clayton L. Camic, Terry J. Housh, Glen O. Johnson, Michelle Mielke, Jorge M. Zuniga, Russell Hendrix, Richard J. SchmidtAbstract: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.
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an emg frequency based test for estimating the neuromuscular Fatigue Threshold during cycle ergometry
European Journal of Applied Physiology, 2010Co-Authors: Clayton L. Camic, Terry J. Housh, Glen O. Johnson, Michelle Mielke, Jorge M. Zuniga, Russell C Hendrix, Richard J. SchmidtAbstract:The purposes of this investigation were twofold: (1) to determine if the model used for estimating the physical working capacity at the Fatigue Threshold (PWCFT) from electromyographic (EMG) amplitude data could be applied to the frequency domain of the signal to derive a new Fatigue Threshold for cycle ergometry called the mean power frequency Fatigue Threshold (MPFFT), and (2) to compare the power outputs associated with the PWCFT, MPFFT, ventilatory Threshold (VT), and respiratory compensation point (RCP). Sixteen men [mean (SD) age = 23.4 (3.2) years] performed incremental cycle ergometer rides to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis. There were significant (p < 0.05) mean differences for PWCFT [mean (SD) = 168 (36) W] versus MPFFT [208 (37) W] and VT [152 (33) W] versus RCP [205 (84) W], but no mean differences for PWCFT versus VT or MPFFT versus RCP. The mean difference between PWCFT and MPFFT may be due to the effects of specific metabolites that independently influence the time and frequency domains of the EMG signal. These findings indicated that the PWCFT model could be applied to the frequency domain of the EMG signal to estimate MPFFT. Furthermore, the current findings suggested that the PWCFT may demarcate the moderate from heavy exercise domains, while the MPFFT demarcates heavy from severe exercise intensities.
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A mechanomyographic frequency-based Fatigue Threshold test.
Journal of neuroscience methods, 2009Co-Authors: C. Russell Hendrix, Clayton L. Camic, Terry J. Housh, Glen O. Johnson, Michelle Mielke, Jorge M. Zuniga, Richard J. SchmidtAbstract:A B 5 T R ACT Theoretically, the mechanomyographic (MMG) mean power frequency Fatigue Threshold (MMGMPFFf ) describes the maximal isometric torque that can be maintained for an extended period of time with no change in the global firing rate of the unfused, activated motor units. Purpose: The purposes of this study were twofold: (1) to determine if the mathematical model for esti mating the electromyographic (EMG) MPFFf 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 MMG MPF Ff : and (2) to compare the mean torque levels derived from the MMG MPF Ff test for the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) muscles during isometric leg extension muscle actions. Methods: Nine adults (4 men and 5 women: mean ±S.D. age = 21.6 ± 1.2 years) 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 exhaustion. Surface MMG signals were recorded from the VL, VM,and RF muscles during each fatiguing isometric muscle action. The MMG MPFFf was defined as the y-intercept of the isometric torque versus slope coefficient (MMGMPF versus time) plot. Results: There were no significant differences among the MMG MPFFf values for the VL, VM, and RF
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An EMG frequency-based test for estimating the neuromuscular Fatigue Threshold during cycle ergometry
European Journal of Applied Physiology, 2009Co-Authors: Clayton L. Camic, C. Russell Hendrix, Terry J. Housh, Glen O. Johnson, Michelle Mielke, Jorge M. Zuniga, Richard J. SchmidtAbstract:The purposes of this investigation were twofold: (1) to determine if the model used for estimating the physical working capacity at the Fatigue Threshold (PWC_FT) from electromyographic (EMG) amplitude data could be applied to the frequency domain of the signal to derive a new Fatigue Threshold for cycle ergometry called the mean power frequency Fatigue Threshold (MPF_FT), and (2) to compare the power outputs associated with the PWC_FT, MPF_FT, ventilatory Threshold (VT), and respiratory compensation point (RCP). Sixteen men [mean (SD) age = 23.4 (3.2) years] performed incremental cycle ergometer rides to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis. There were significant ( p
