Intramuscular pressure and tissue oxygenation during low-force static contraction do not underlie muscle fatigue (original) (raw)
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Acta Physiologica Scandinavica, 1997
This study investigated changes in intramuscular pressure (IMP) and surface electromyographic (EMG) parameters (mean frequency of the power spectrum, f mean ; and signal amplitude denoted as root mean square, RMS) during contractions to fatigue at 25 and 70% of maximal voluntary contraction (MVC). Parameters were recorded simultaneously from the vastus lateralis muscle during knee extension. A signi®cant decrease in f mean occurred with time at both contraction levels; however, the rate of decline (slope) was greater at 70% MVC. RMS increased throughout the contractions at both levels, with the relative increase being signi®cantly greater for 25% MVC. IMP increased during 25% MVC but did not change during the 70% MVC contraction. IMP at rest was signi®cantly higher post-contractions than it was pre-contractions at 25% MVC (21.1 vs. 8.0 mmHg, P < 0.01) and 70% MVC (13.7 vs. 8.6 mmHg, P < 0.01). Consequently, post-contraction IMP was higher at 25% MVC than at 70% MVC (P < 0.01). IMP changes throughout the fatiguing contractions correlated negatively with f mean and positively with RMS at both MVC levels; however, these correlations were better at 25% MVC. The extent of intramuscular water accumulation is discussed as a major cause of the difference in IMP changes between 25% and 70% MVC. Signi®cant differences in the rate of change for all parameters between high vs. low contraction levels may suggest a common mechanism governing changes in IMP and EMG fatigue indicators.
Journal of Applied Physiology, 2004
Søgaard. Intramuscular pressure and EMG relate during static contractions but dissociate with movement and fatigue. pressure (IMP) and electromyography (EMG) mirror muscle force in the nonfatigued muscle during static contractions. The present study explores whether the constant IMP-EMG relationship with increased force may be extended to dynamic contractions and to fatigued muscle. IMP and EMG were recorded from shoulder muscles in three sessions: 1) brief static arm abductions at angles from 0 to 90°, with and without 1 kg in the hands; 2) dynamic arm abductions at angular velocities from 9 to 90°/s, with and without 1 kg in the hands; and 3) prolonged static arm abduction at 30°for 30 min followed by recovery. IMP and EMG increased in parallel with increasing shoulder torque during brief static tasks. During dynamic contractions, peak IMP and EMG increased to values higher than those during static contractions, and EMG, but not IMP, increased significantly with speed of abduction. In the nonfatigued supraspinatus muscle, a linear relationship was found between IMP and EMG; in contrast, during fatigue and recovery, significant timewise changes of the IMP-to-EMG ratio occurred. The results indicate that IMP should be included along with EMG when mechanical load sharing between muscles is evaluated during dynamic and fatiguing contractions.
Journal of Applied Physiology, 2004
Intramuscular pressure (IMP) and EMG mirror muscle force in the non-fatigued muscle during static contractions. The present study explores if the constant IMP/EMG relationship with increased force may be extended to dynamic contractions and to fatigued muscle. IMP and EMG were recorded from shoulder muscles in three sessions: 1) brief static arm abductions at angles from 0 -90° with and without 1 kg in the hands, 2) dynamic arm abductions at velocities from 9 -90°/s with and without 1 kg in the hands, and 3) prolonged static arm abduction at 30° for 30 min followed by recovery. IMP and EMG increased in parallel with increasing shoulder torque during brief static tasks. During dynamic contractions peak IMP and EMG increased to values higher than those during static contractions; and EMG, but not IMP, increased significantly with speed of abduction. In the non-fatigued m. supraspinatus a linear relationship was found between IMP and EMG; in contrast, during fatigue and recovery significant time-wise changes of the IMP/EMG ratio occurred. The results indicate that IMP should be included along with EMG when evaluating mechanical load sharing between muscles during dynamic and fatiguing contractions.
Scandinavian Journal of Medicine and Science in Sports
This study aimed to compare the magnitude and etiology of neuromuscular fatigue during maximal repeated contractions performed in two contraction modes (concentric vs isometric) and at two contraction velocities (30°/s vs 240°/s). Eleven lower limb-trained males performed 20 sets of maximal contractions at three different angular velocities: 0°/s (KE0), 30°/s (KE30), and 240°/s (KE240). Cumulated work, number of contraction, duty cycle, and contraction time were controlled. Torque, superimposed and resting twitches, as well as gas exchange, were analyzed. Increasing contraction velocity was associated with greater maximal voluntary torque loss (KE0: −9.8 ± 3.9%; KE30: −16.4 ± 8.5%; KE240: −32.6 ± 6.3%; P < 0.05). Interestingly, the torque decrease was similar for a given cumulated work. Compared with KE0, KE240 generated a greater evoked torque loss (Db100: −24.3 ± 5.3% vs −5.9 ± 6.9%; P < 0.001), a higher O2 consumption (23.7 ± 6.4 mL/min/kg vs 15.7 ± 3.8 mL/min/ kg; P < 0...
EMG spectral indices and muscle power fatigue during dynamic contractions
2009
The purpose of this study was to examine acute exercise-induced changes on muscle power output and surface electromyography (sEMG) parameters (amplitude and spectral indices of muscle fatigue) during a dynamic fatiguing protocol. Fifteen trained subjects performed five sets consisting of 10 leg presses (10RM), with 2 min rest between sets. Surface electromyography was recorded from vastus medialis (VM) and lateralis (VL) and biceps femoris (BF) muscles. A number of EMG-based parameters were compared for estimation accuracy and sensitivity to detect peripheral muscle fatigue. These were: Mean Average Voltage, median spectral frequency, Dimitrov spectral index of muscle fatigue (FI nsm5 ), as well as other parameters obtained from a time-frequency analysis (Choi-Williams distributions) such as mean and variance of the instantaneous frequency and frequency variance. The log FI nsm5 as a single parameter predictor accounted for 37% of the performance variance of changes in muscle power and the log FI nsm5 and MFM as a two factor combination predictor accounted for 44%. Peripheral impairments assessed by sEMG spectral index FI nsm5 may be a relevant factor involved in the loss of power output after dynamic high-loading fatiguing task.
The Importance of Electromyography and Contraction Mechanogram in the Study of Muscular Fatigue
2000
Introduction: A controversial topic in physiology is muscular fatigue, raising still unanswered questions regarding its causes and mechanisms. Aims: To investigate the role of electromyography and contraction mechanogram in the evaluation of muscular fatigue and to establish the circumstances that ensures a greater physical effort with a lesser degree of muscular fatigue. Materials: Ten healthy subjects in whom we recorded the global surface electromyogram (SEMG) and muscular contraction mechanogram using a Medicore (type MG 42) electromyograph (produced in Hungary), respectively a BIOPAC system (USA). Muscular recordings were stored and subsequently processed using two personal computers. Methods: The study was performed on ten healthy subjects, of both genders and similar ages, and consisted in the recording of global surface electromyography (SEMG) and mechanogram of the voluntary maximal isometric contractions of the finger flexor in two different sessions of physical effort:-voluntary maximal isometric contractions of short duration (high frequency-Hi)-4 sec, followed by rest intervals of 6 sec-30 contractions in 5 min;-voluntary maximal isometric contractions of longer duration (low frequency-Lo)-40 sec, with rest intervals of 60 sectotal 3 contractions in 5 minutes. In both cases, during the 5-minute sessions, the subjects contracted the finger flexor for 120 sec, while the total rest period was 180 seconds. Results: The results are synthetically represented in several tables. Conclusions: When the muscular contractions and the resting intervals are shorter, the total global physical effort performed in the same unit of time is 32% greater and with less fatigue, than when muscular contractions and resting intervals are longer.
Variability and interrelationships of surface EMG parameters during local muscle fatigue
Muscle & Nerve, 1993
The inter‐and intraindividual variability of the frequency power density spectral and surface EMG amplitude parameters and of the muscle fiber conduction velocity (MFCV) is studied in 26 healthy volunteers during fatiguing isometric ischemic intermittent exercise of the m, biceps brachii at 80% of the maximal voluntary contraction level, with a contraction rate of 30/min. No significant age effects were found. Males were significantly stronger compared with females. The higher initial SEMG amplitude and the strongershift of the frequency power density spectrum (PDS) to lower frequencies appear to be significantly correlated with males. Fatigue induces an almost proportional compression of the SEMG frequency content. The muscle fiber conduction velocity has the highest intraindividual reproducibility (r = 0.81). Despite the definite and strong influence of the MFCV on the PDS, the shift of the PDS can not be explained by a change of MFCV alone.© 1993 John Wiley & Sons, Inc.