The influence of the muscle fiber pennation angle and innervation zone on the identification of neuromuscular fatigue during cycle ergometry (original) (raw)
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Journal of Neuroscience Methods, 2009
The purposes of this study were threefold: (1) to compare the power output related patterns of absolute and normalized EMG amplitude and MPF responses for electrode orientations that were approximately parallel and perpendicular to the muscle fibers of the vastus lateralis muscle (VL); (2) to examine the influence of electrode orientation on mean absolute EMG amplitude and MPF values; and (3) to determine the effects of normalization on mean EMG amplitude and MPF values from parallel and perpendicular electrode orientations. Twenty adults (10 men and 10 women mean ± SD age = 23.4 ± 3.6 years) performed incremental cycle ergometry tests to exhaustion. Two sets of bipolar surface EMG electrodes were placed approximately parallel and perpendicular to the muscle fibers over the VL. Paired t-tests indicated that absolute EMG amplitude values for the parallel electrode orientation were greater (p < 0.05) at 50, 75, and 100 W. The normalized EMG amplitude also had greater values for the parallel electrode orientation at 75 and 100 W. For absolute EMG MPF, the parallel electrode orientation had greater values for all six power outputs, but after normalization, the perpendicular electrode orientation had a greater value at 75 W. Ten percent of the subjects exhibited different power output related patterns of responses between electrode orientations for EMG amplitude and 35% exhibited different patterns for MPF. These findings indicated that normalization reduced, but did not eliminate the influence of electrode orientation and highlighted the importance of standardizing electrode orientation to compare EMG values during cycle ergometry.
European Journal of Applied Physiology, 2010
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 \ 0.05) mean differences for PWC FT [mean (SD) = 168 (36) W] versus MPF FT [208 (37) W] and VT [152 (33) W] versus RCP [205 (84) W], but no mean differences for PWC FT versus VT or MPF FT versus RCP. The mean difference between PWC FT and MPF FT 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 PWC FT model could be applied to the frequency domain of the EMG signal to estimate MPF FT . Furthermore, the current findings suggested that the PWC FT may demarcate the moderate from heavy exercise domains, while the MPF FT demarcates heavy from severe exercise intensities. Keywords Mean power frequency Á Physical working capacity at the fatigue threshold Communicated by Susan Ward.
Journal of Applied Physiology, 2014
A rapid switch from hyperbolic to isokinetic cycling allows the velocity-specific decline in maximal power to be measured, i.e., fatigue. We reasoned that, should the baseline relationship between isokinetic power (Piso) and electromyography (EMG) be reproducible, then contributions to fatigue may be isolated from 1) the decline in muscle activation (muscle activation fatigue); and 2) the decline in Piso at a given activation (muscle fatigue). We hypothesized that the EMG-Piso relationship is linear, velocity dependent, and reliable for instantaneous fatigue assessment at intolerance during and following whole body exercise. Healthy participants ( n = 13) completed short (5 s) variable-effort isokinetic bouts at 50, 70, and 100 rpm to characterize baseline EMG-Piso. Repeated ramp incremental exercise tests were terminated with maximal isokinetic cycling (5 s) at 70 rpm. Individual baseline EMG-Piso relationships were linear ( r2 = 0.95 ± 0.04) and velocity dependent (analysis of cov...
2013
Introduction: The purposes of the current investigation were to determine the: 1) reproducibility of the patterns of responses for electromyographic (EMG) amplitude; and 2) intraclass correlation coefficient (ICC) of the EMG amplitude during three incremental cycle ergometer tests separated by 48 hours. Methods: Ten men performed incremental cycle ergometry tests to exhaustion on three separate occasions. Surface EMG amplitude was recorded simultaneously from the three superficial quadriceps muscles at each trial. Results: The results of the polynomial regression indicated that, for >95% of the cases, the best-fit model was the same at each trial for EMG amplitude. The ICC values were high for EMG amplitude indicating excellent reliability. Discussion: These results indicate that EMG amplitude is a reliable measure of motor unit activation strategy during incremental cycle ergometry. Abstract No. 2 (Student_Graduate)
Response of electromyographic variables during incremental and fatiguing cycling
Medicine & Science in …, 2008
Purpose: Surface electromyographic (EMG) variables allow study of the electrical activity of motor units within active skeletal muscle. Recent methodological advances permit the estimation of muscle fiber conduction velocity (MFCV) from EMG signals recorded during dynamic exercise. However, EMG responses to incremental and fatiguing cycling are poorly understood. Methods: Twenty males completed an incremental cycling protocol (20, 40, 60, and 80% of peak power output, PPO) on two occasions separated by five days. The final stage was six minutes long to induce muscle fatigue. EMG signals were recorded from the vastus lateralis and vastus medialis muscles, and root mean square (RMS) and MFCV were estimated. Results: For incremental exercise, EMG data were reliable between trials, especially for MFCV in the vastus lateralis at 40, 60 and 80% PPO (e.g. coefficient of variation < 6.3%; bias < 0.4 m·s -1 ; limits of agreement < 1.2 m·s -1 ). Significant positive correlations were observed between RMS and MFCV (r = 0.79 to 0.83), as both measures increased with power output (repeated measures analysis of variance all p = 0.001). For fatiguing exercise, many EMG variables showed systematic bias between trials. RMS (p = 0.009 to 0.051) but not MFCV (p = 0.236 -0.578) significantly increased during fatiguing cycling. Conclusions: During dynamic cycle exercise, EMG variables are reliable and increase with power output. During fatiguing exercise, EMG variables may be sensitive to learning effects in the execution of the task. MFCV and RMS are correlated with varying power output in the un-fatigued muscle but not during the development of fatigue.
Journal of sports science & medicine, 2016
Recently, a new method has been proposed to detect the onset of neuromuscular fatigue during an incremental cycling test by assessing the changes in spectral electromyographic (sEMG) frequencies within individual exercise periods of the test. The method consists on determining the highest power output that can be sustained without a significant decrease in spectral frequencies. This study evaluated the validity of the new approach by assessing the changes in spectral indicators both throughout the whole test and within individual exercise periods of the test. Fourteen cyclists performed incremental cycle ergometer rides to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis. The mean and median frequencies (Fmean and Fmedian, respectively) of the sEMG power spectrum were calculated. The main findings were: (1) Examination of spectral indicators within individual exercise periods of the test showed that neither Fmean nor Fmedian decreased significantly duri...
Journal of Electromyography and Kinesiology, 2001
The purpose of this investigation was to determine the relationships for mechanomyographic (MMG) amplitude, MMG mean power frequency (MPF), electromyographic (EMG) amplitude, and EMG MPF versus power output during incremental cycle ergometry. Seventeen adults volunteered to perform an incremental test to exhaustion on a cycle ergometer. The test began at 50 W and the power output was increased by 30 W every 2 min until the subject could no longer maintain 70 rev min Ϫ1 . The MMG and EMG signals were recorded simultaneously from the vastus lateralis during the final 10 s of each power output and analyzed. MMG amplitude, MMG MPF, EMG amplitude, EMG MPF, and power output were normalized as a percentage of the maximal value from the cycle ergometer test. Polynomial regression analyses indicated that MMG amplitude increased (PϽ0.05) linearly across power output, but there was no change (PϾ0.05) in MMG MPF. EMG amplitude and MPF were fit best (PϽ0.05) with quadratic models. These results demonstrated dissociations among the time and frequency domains of MMG and EMG signals, which may provide information about motor control strategies during incremental cycle ergometry. The patterns for amplitude and frequency of the MMG signal may be useful for examining the relationship between motor-unit recruitment and firing rate during dynamic tasks.
European Journal of Applied Physiology, 1997
The electromyogram (EMG) median power frequency of the vastus lateralis and flexor digitorum superficialis muscles was measured in 12 subjects during cycle ergometry with step-wise increasing exercise intensities up to 100% of V O 2max. Blood lactate concentration was measured to investigate the relationship between changes in lactate concentration and shifts in the EMG median power frequency of exercising vastus lateralis and non-exercising flexor digitorum superficialis muscles. The results indicated that lactate concentration did not systematically affect median frequency: in spite of a considerable increase in blood lactate concentration, no systematic decrease of the median frequency during exercise was found, either for the vastus lateralis or for the flexor digitorum superficialis muscles. Instead of a decrease of the median frequency during exercise, as seen in isometrical protocols, an increase was seen in most subjects. An interesting finding was a decrease of the median frequency of vastus lateralis muscle during recovery in 8 subjects. The present findings showed that the relationship between EMG frequency decrease, lactate accumulation and fatigue, as observed in isometric protocols, cannot be simply applied to dynamic exercise.
1995
Changes in muscle activity occur with changes in cycling cadence and power output. An understanding of these changes can aid in strength training and performance evaluation. Although the integrated EMG has been frequently studied, phasic muscle activity is evaluated less often. Phasic activity was measured relative to the crank position from 0o at top dead center (TDC) through a fill revolution. Four muscles on three experienced recreational cyclists were monitored at cadences of 60rpm, 80rpq and l00rpm and at power levels of 150W, 300W, and 450W. Surface electrodes and videography were utilized to determine the start and stop position of muscle activity relative to each crank revolution. A fill-rectification of the raw EMG signal was then used to determine activity above the threshold. Rectus femoris activity started earlier in the crank cycle with each increase in cadence. However, it stopped later for only the first increment in cadence and remained constant for the second. These...