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

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

doi:10.1007/s00421-009-1206-3

Cited by 21 publications

(20 citation statements)

References 64 publications

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“…The amplitude is fluctuating within broad ranges, and outliers have huge influence. To avoid this, instead of the raw amplitude, an expression of the mean value of a short time window is used to characterize the amplitude (Arabadzhiev et al., 2010). An arithmetic mean of the raw signal would provide a value close to zero; therefore, the signal is squared before calculation of the mean and then to even out the square effect, the root is applied.…”

Section: Methodsmentioning

confidence: 99%

Patterns of muscle activation during generalized tonic and tonic-clonic epileptic seizures

et al. 2011

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Summary Purpose: Tonic seizures and the tonic phase of tonic–clonic epileptic seizures are defined as “sustained tonic” muscle contraction lasting a few seconds to minutes. Visual inspection of the surface electromyogram (EMG) during seizures contributed considerably to a better understanding and accurate diagnosis of several seizure types. However, quantitative analysis of the surface EMG during the epileptic seizures has received surprisingly little attention until now. The aim of our study was to elucidate the pathomechanism of the tonic muscle activation during epileptic seizures. Methods: Surface EMG was recorded from the deltoid muscles, on both sides, during 63 seizures from 20 patients with epilepsy (10 with generalized tonic and 10 with tonic–clonic seizures). Twenty age‐ and gender‐matched normal controls simulated 100 generalized tonic seizures. To characterize the signal properties we calculated the root mean square (RMS) of the amplitudes, the median frequency (MF), and the coherence. Based on the spectrograms of both epileptic and simulated seizures, we chose to determine the relative spectral power (RP) in the higher (100–500 Hz) frequency domain. Key Findings: During the tonic seizures there was a significant shift toward higher frequencies, expressed by an increase in the MF and the RP (100–500 Hz). The amplitude characteristic of the signal (RMS) was significantly higher during the tonic phase of the tonic–clonic seizures as compared to the simulated ones, whereas the RMS of the tonic seizures was significantly lower than the simulated ones. The EMG–EMG coherence was significantly higher during the epileptic seizures (both types) as compared to the simulated ones. Significance: Our results indicate that the mechanism of muscle activation during epileptic seizures is different from the physiologic one. Furthermore the sustained muscle activation during the tonic phase of tonic–clonic seizures is different from that during tonic seizures: The tonic phase of tonic–clonic seizures is characterized by increased amplitude of the signal, whereas tonic seizures are produced by a significant increase in the frequency of the signal.

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Section: Methodsmentioning

confidence: 99%

Patterns of muscle activation during generalized tonic and tonic-clonic epileptic seizures

et al. 2011

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“…1 (Arabadzhiev et al 2010a). The coefficient values used for the computation of the different assumed IAPs were given in Table 2.…”

Section: Methodsmentioning

confidence: 95%

“…The synchrony level was estimated by the population synchrony index (PSI) proposed in the same publication (Yao et al 2000). The exact procedure for achieving the desired stage of synchrony was described elsewhere (Arabadzhiev et al 2010a). For the intermediate synchrony stage (denoted as S1) we synchronized 5% of the discharges of the referent MUs with the closest discharges of 5% of the rest of the MUs.…”

Section: Methodsmentioning

confidence: 99%

“…For the intermediate synchrony stage (denoted as S1) we synchronized 5% of the discharges of the referent MUs with the closest discharges of 5% of the rest of the MUs. For the high synchrony stage (denoted as S2) these numbers were set to 10% (Arabadzhiev et al 2010a;Yao et al 2000). We used random variability in the discharge alignment within the range from -2 to ?2 ms (Arabadzhiev et al 2010a;Yao et al 2000), with uniform distribution.…”

Section: Methodsmentioning

confidence: 99%

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The spectral changes in EMG during a second bout eccentric contraction could be due to adaptation in muscle fibres themselves: a simulation study

et al. 2011

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The mechanism of marked reduction in damage symptoms after repeated bout of similar eccentric contractions is still unknown. The neuronal adaptation leading to reduction of muscle fibre propagation velocity (MFPV) due to increased activation of slow-twitch motor units (MUs), decrease in activation of fast-twitch MUs, and/or increase in MU synchronization was suggested as a cause for lower EMG frequency characteristics. However, the repeated bout effect could occur also after electrically stimulated exercise. Prolonged elevation of cytoplasmic Ca(2+) due to the increased membrane permeability after eccentric contractions was reported. Elevated Ca(2+) induced peripheral changes that included alteration of intracellular action potential and MFPV reduction. We simulated and compared changes in EMG frequency characteristics related to effects of central nervous system (CNS) or to peripheral changes. The simulations were performed for different electrode arrangements and positions. The results showed that the peripheral effects could be similar or even stronger than the effects related to CNS. We hypothesised that the repeated bout effect was a consequence of the adaptation in muscle fibres necessary for avoiding Ca(2+)-induced protein and lipid degradation due to Ca(2+) overload resulting from the increased membrane permeability after eccentric contraction. The possibilities for noninvasive testing of this hypothesis were discussed.

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“…Changes in the IAP spike duration produced by fatigue conditions have been hypothesized to be at the root of the changes observed in the characteristics of surface potentials (Cupido et al, 1996;Dimitrova and Dimitrov, 2002;Arabadzhiev et al, 2010). So far, however, no attempt has been made to establish experimentally a direct cause-effect relationship between fatigue-based IAP widening and alterations in extracellular potentials.…”

Section: Applicability Of the Parameter Npd To Future Studiesmentioning

confidence: 94%

Estimating the duration of intracellular action potentials in muscle fibres from single-fibre extracellular potentials

Rodríguez

Navallas

Gila

et al. 2011

Journal of Neuroscience Methods

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

Cited by 21 publications

References 64 publications

Patterns of muscle activation during generalized tonic and tonic-clonic epileptic seizures

Patterns of muscle activation during generalized tonic and tonic-clonic epileptic seizures

The spectral changes in EMG during a second bout eccentric contraction could be due to adaptation in muscle fibres themselves: a simulation study

Estimating the duration of intracellular action potentials in muscle fibres from single-fibre extracellular potentials

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