Interpretation of EMG integral or RMS and estimates of “neuromuscular efficiency” can be misleading in fatiguing contraction

Arabadzhiev, Todor I.; Dimitrov, Vladimir G.; Dimitrova, Nonna A.; Dimitrov, George

doi:10.1016/j.jelekin.2009.01.008

Cited by 93 publications

(68 citation statements)

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“…These changes in median frequency are probably associated with the recruitment of additional motor units over the course of repetitions to partially compensate for the loss of force of the motor units that are already active (Bigland-Ritchie et al 1986;Fuglevand et al 1993;Kellis 1999). Although different hypothesis have been advanced (Basmajian and DeLuca 1985;Gandevia 2001), several authors suggest that these changes in median frequency and in the recruitment of motor units are causes, at least in part, of the observed increase in the surface MRV amplitude (Arabadzhiev et al 2010;De-Luca 1984;Gandevia 2001). The fatigue of the fast motor unit associated with the decrease in intra-muscular pH and lactate accumulation is in agreement with previous biochemical studies using high-intensity cycling (Casey et al 1996;McCartney et al 1983) sprinting in a non-motorised treadmill (Greenhaff et al 1994), knee extension exercise or electrically evoked isometric contractions (Soderlund et al 1992) showing that the development of fatigue observed under these conditions may be attributable in part to accumulation of muscle lactate and H ?…”

Section: Discussionmentioning

confidence: 99%

“…The increase observed over the repetitions in the agonist activity level at the angular positions of higher neural activation (90-67°) has been observed in VM during isometric fatigue test (Weir et al 1996) and during maximal isokinetic concentric efforts of the knee extensors (Kellis 1999). As explained above, this increased agonist activity has been related to an attempt of the central nervous system to compensate for the failing muscle by increasing the motor units available (De-Luca 1984;Enoka 1995;Kellis 1999) and/or to a shift towards lower frequencies due to reduction in the muscle fibre conduction velocity (Aagaard et al 2000;Basmajian and DeLuca 1985) and to lengthening of the intra-cellular action potential (Arabadzhiev et al 2010;De-Luca 1984;Gandevia 2001). The considerable increase in the antagonist BF muscle activity observed during exercise in the present study has been also found during intermittent submaximal isometric (Psek and Cafarelli 1993) or isokinetic (Hassani et al 2006) knee extension contractions suggesting that the decline in the mechanical output of the knee extensors immediately after fatigue may be due, in part, to increased force exerted by the antagonist muscle (Bentley et al 2000).…”

Section: Agonist and Antagonist Coactivationmentioning

confidence: 99%

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Blood lactate and sEMG at different knee angles during fatiguing leg press exercise

et al. 2011

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The purpose of this study was to examine the changes in peak power output, blood lactate concentrations and surface electromyographic activity (sEMG) of the agonist [vastus lateralis (VL) and vastus medialis (VM)] and the antagonist [biceps femoris (BF)] muscles at two angular positions intervals (90-67° and 23-0° of knee flexion), during a set of 10 repetitions leading to failure of bilateral leg press exercise. Fatiguing exercise resulted in increased blood lactate concentrations, the agonist mean rectified voltage (MRV) at 90-67° of flexion, the antagonist average MRV at 23-0° of flexion and the spectral parameter proposed by Dimitrov (FI(nsm5)) (P < 0.01-0.05). Significant decreases (P < 0.01-0.05) were observed in power output, median frequency (F(med)) of the agonist muscles at both angular position intervals and of the antagonist muscle at 90-67° of flexion. No changes were observed in the antagonist/agonist MRV activation ratio. The present data suggest that the shift of frequency spectrum to lower frequencies and the accumulation of lactate and/or H(+), but not the antagonist/agonist MRV activation ratio, may be relevant independent factors associated with fatigue.

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Section: Discussionmentioning

confidence: 99%

Section: Agonist and Antagonist Coactivationmentioning

confidence: 99%

Blood lactate and sEMG at different knee angles during fatiguing leg press exercise

et al. 2011

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“…Because the motor units recruited from the beginning of a fatiguing contraction exhibit a progressive decrease in discharge rate (Mottram et al 2005;Rudroff et al 2011), the increase in EMG amplitude is generally attributed to the recruitment of additional motor units Gandevia 2001) but can also be influenced by changes in the conduction velocity of motor unit action potentials and the synchronization of motor unit discharge times (Arabadzhiev et al 2010;Yao et al 2000). Although the newly recruited motor units will initially increase discharge rate, they, too, will eventually reduce discharge rate, and additional motor units will be recruited (Carpentier et al 2001).…”

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confidence: 99%

Increase in heterogeneity of biceps brachii activation during isometric submaximal fatiguing contractions: a multichannel surface EMG study

Staudenmann

Dieën

Stegeman

et al. 2014

Journal of Neurophysiology

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Staudenmann D, van Dieën JH, Stegeman DF, Enoka RM. Increase in heterogeneity of biceps brachii activation during isometric submaximal fatiguing contractions: a multichannel surface EMG study. J Neurophysiol 111: 984 -990, 2014. First published December 11, 2013 doi:10.1152/jn.00354.2013.-The effects of fatigue emerge from the beginning of sustained submaximal contractions, as shown by an increase in the amplitude of the surface electromyogram (EMG). The increase in EMG amplitude is attributed to an augmentation of the excitatory drive to the motor neuron pool that, more importantly than increasing discharge rates, recruits additional motor units for the contraction. The aim of this study was to determine whether the spatiotemporal distribution of biceps brachii (BB) activity becomes more or less heterogeneous during a fatiguing isometric contraction sustained at a submaximal target force. Multiple electrodes were attached over the entire BB muscle, and principal component analysis (PCA) was used to extract the representative information from multiple monopolar EMG channels. The development of heterogeneity during the fatiguing contraction was quantified by applying a cluster algorithm on the PCA-processed EMG amplitudes. As shown previously, the overall EMG amplitude increased during the sustained contraction, whereas there was no change in coactivation of triceps brachii. However, EMG amplitude did not increase in all channels and even decreased in some. The change in spatial distribution of muscle activity varied across subjects. As found in other studies, the spatial distribution of EMG activity changed during the sustained contraction, but the grouping and size of the clusters did not change. This study showed for the first time that muscle activation became more heterogeneous during a sustained contraction, presumably due to a decrease in the strength of common inputs with the recruitment of additional motor units.

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“…The effect of changes in intracellular action potential (IAP) on EMG amplitude characteristics is often not taken into account, although there is a consensus on IAP changes with consecutive discharges and fatigue. Elongation of IAP spatial profile in active muscle fibers could also increase surface EMG amplitude (Arabadzhiev et al 2008a;Arabadzhiev et al 2009;Dimitrov et al 2008;Dimitrova and Dimitrov 2003;Dimitrova and Dimitrov 2006). Therefore, one should be able to discriminate between the effects of central and peripheral factors, to assure that the increased amplitude of surface EMG signals during oxygen uptake slow component or following training is due to neural adaptations.…”

Section: Introductionmentioning

confidence: 99%

Influence of motor unit synchronization on amplitude characteristics of surface and intramuscularly recorded EMG signals

et al. 2009

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The increase in muscle strength without noticeable hypertrophic adaptations is very important in some sports. Motor unit (MU) synchronisation and higher rate of MU activation are proposed as possible mechanisms for such a strength and electromyogram (EMG) increase in the early phase of a training regimen. Root mean square and/or integrated EMG are amplitude measures commonly used to estimate the adaptive changes in efferent neural drive. EMG amplitude characteristics could change also because of alteration in intracellular action potential (IAP) spatial profile. We simulated MUs synchronization under different length of the IAP profile. Different synchronization was simulated by variation of the percent of discharges in a referent MU, to which a variable percent of remaining MUs was synchronized. Population synchrony index estimated the degree of MU synchronization in EMG signals. We demonstrate that the increase in amplitude characteristics due to MU synchronization is stronger in surface than in intramuscularly detected EMG signals. However, the effect of IAP profile lengthening on surface detected EMG signals could be much stronger than that of MU synchronization. Thus, changes in amplitude characteristics of surface detected EMG signals with progressive strength training could hardly be used as an indicator of changes in neural drive without testing possible changes in IAPs.

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Interpretation of EMG integral or RMS and estimates of “neuromuscular efficiency” can be misleading in fatiguing contraction

Cited by 93 publications

References 68 publications

Blood lactate and sEMG at different knee angles during fatiguing leg press exercise

Blood lactate and sEMG at different knee angles during fatiguing leg press exercise

Increase in heterogeneity of biceps brachii activation during isometric submaximal fatiguing contractions: a multichannel surface EMG study

Influence of motor unit synchronization on amplitude characteristics of surface and intramuscularly recorded EMG signals

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