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McManus, Lara M.
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McManus, Lara M.
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McManus, Lara M.
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Now showing 1 - 10 of 12
- PublicationAlterations in Motor Unit Firing Rate and Action Potential Properties during Isometric Fatigue in Stroke Survivors(2016-07-08)
; ; ; ; The limited number of studies that have investigated fatigue in chronic stroke survivors during voluntary contr actions to the endurance limit have reported relatively higher central fatigue and lower peripher al fatigue on the affected side when compared to the less-affected side and healthy controls (Riley and Bilodeau, 2002; Knorr et al., 2011). Although these changes have been investigated using global indices of motor unit (MU) activation, alterations at th e level of the single motor unit have not yet been examined.167 - PublicationEMG Driven Model of the Lumbar Spine during Flexion, Bending and Rotation Using Opensim(2013-08-09)
; ; ; This study utilised the OpenSim platform to develop an EMG driven model of the lumbar spine by expanding an existing model and incorporating a plugin to represent intervertebral stiffness. Subject-specific kinematic data and surface EMG activity were recorded from 4 subjects during flexion and extension, lateral bending, and axial rotation. The model was used to predict muscle excitation patterns necessary to produce the recorded motions, and the patterns were compared with the recorded EMG data. The model was then driven with the recorded EMG data, and new excitation patterns were calculated for the deep muscles for which EMG data was not available. Simulations were conducted for intervertebral lumbar stiffness corresponding to preloading of 0N, 250N and 500N. The model-predicted excitation patterns were most comparable to recorded EMG data for the flexion and extension motions. Excitation levels predicted for all motions were sensitive to the applied preload. Although activation patterns remained similar, there was a substantial variation in model-predicted muscle excitation levels with change in intervertebral stiffness.191 - PublicationChanges in motor unit behavior following isometric fatigue of the first dorsal interosseous muscle(American Psychological Society, 2015-05-01)
; ; ; ; The neuromuscular strategies employed to compensate for fatigue-induced muscle force deficits are not clearly understood. This study utilizes surface electromyography (sEMG) together with recordings of a population of individual motor unit action potentials (MUAPs) to investigate potential compensatory alterations in motor unit (MU) behavior immediately following a sustained fatiguing contraction and after a recovery period. EMG activity was recorded during abduction of the first dorsal interosseous in 12 subjects at 20% maximum voluntary contraction (MVC), before and directly after a 30% MVC fatiguing contraction to task failure, with additional 20% MVC contractions following a 10-min rest. The amplitude, duration and mean firing rate (MFR) of MUAPs extracted with a sEMG decomposition system were analyzed, together with sEMG root-mean-square (RMS) amplitude and median frequency (MPF). MUAP duration and amplitude increased immediately postfatigue and were correlated with changes to sEMG MPF and RMS, respectively. After 10 min, MUAP duration and sEMG MPF recovered to prefatigue values but MUAP amplitude and sEMG RMS remained elevated. MU MFR and recruitment thresholds decreased postfatigue and recovered following rest. The increase in MUAP and sEMG amplitude likely reflects recruitment of larger MUs, while recruitment compression is an additional compensatory strategy directly postfatigue. Recovery of MU MFR in parallel with MUAP duration suggests a possible role for metabolically sensitive afferents in MFR depression postfatigue. This study provides insight into fatigue-induced neuromuscular changes by examining the properties of a large population of concurrently recorded single MUs and outlines possible compensatory strategies involving alterations in MU recruitment and MFR.392Scopus© Citations 53 - PublicationMotor unit activity during fatiguing isometric muscle contraction in hemispheric stroke survivors(2017-11-24)
; ; ; ; Enhanced muscle weakness is commonly experienced following stroke and may be accompanied by increased susceptibility to fatigue. To examine the contributions of central and peripheral factors to isometric muscle fatigue in stroke survivors, this study investigates changes in motor unit (MU) mean firing rate, and action potential duration during, and directly following, a sustained submaximal fatiguing contraction at 30% maximum voluntary contraction (MVC). A series of short contractions of the first dorsal interosseous muscle were performed pre-and post-fatigue at 20% MVC, and again following a 10-min recovery period, by 12 chronic stroke survivors. Individual MU firing times were extracted using surface EMG decomposition and used to obtain the spike-triggered average MU action potential waveforms. During the sustained fatiguing contraction, the mean rate of change in firing rate across all detected MUs was greater on the affected side (-0.02 ± 0.03 Hz/s) than on the less-affected side (-0.004 ± 0.003 Hz/s, p = 0.045). The change in firing rate immediately post-fatigue was also greater on the affected side than less-affected side (-13.5 ± 20 and 0.1 ± 19%, p = 0.04). Mean MU firing rates increased following the recovery period on the less-affected side when compared to the affected side (19.3 ± 17 and 0.5 ± 20%, respectively, p = 0.03). MU action potential duration increased post-fatigue on both sides (10.3 ± 1.2 to 11.2 ± 1.3 ms on the affected side and 9.9 ± 1.7 to 11.2 ± 1.9 ms on the less-affected side, p = 0.001 and p= 0.02, respectively), and changes in action potential duration tended to be smaller in subjects with greater impairment (p = 0.04). This study presents evidence of both central and peripheral fatigue at the MU level during isometric fatiguing contraction for the first time in stroke survivors. Together, these preliminary observations indicate that the response to an isometric fatiguing contraction differs between the affected and less-affected side post-stroke, and may suggest that central mechanisms observed here as changes in firing rate are the dominant processes leading to task failure on the affected side.366Scopus© Citations 17 - PublicationFatigue-Related Alterations to Intra-Muscular Coherence(IEEE, 2015-04-24)
; ; ; ; Oscillations in the alpha (8-12 Hz), beta (15-35 Hz) and gamma (35-60 Hz) frequency bands are commonly observed in recordings from the primary motor cortex. Coherence analysis based on motor unit spike trains is commonly used to quantify the degree of shared cortical input and the common modulation of motor unit discharge rates between muscles. In this study, intra-muscular coherence is used to investigate the alterations in the neural drive to the First Dorsal Interosseous muscle directly after a fatiguing contraction and following a rest period. An increase in coherence was observed for all frequency bands examined, which was statistically significant within the alpha and beta frequency ranges. There was no consistent difference between the coherence estimates obtained pre-fatigue and those reported after the recovery period. The increase in beta band coherence post-fatigue may indicate increased levels of cortical drive to the motor unit pool. Although the functional significance behind the increase in beta frequency coherence is unclear, it may aid in the coordination of muscle activity to compensate for the decline in the force generating capacity after fatigue.346Scopus© Citations 3 - PublicationMuscle fatigue increases beta-band coherence between the firing times of simultaneously active motor units in the first dorsal interosseous muscle(American Psychological Society, 2016-06-01)
; ; ; ; Synchronization between the firing times of simultaneously active motor units (MUs) is generally assumed to increase during fatiguing contractions. To date, however, estimates of MU synchronization have relied on indirect measures, derived from surface electromyographic (EMG) interference signals. This study used intramuscular coherence to investigate the correlation between MU discharges in the first dorsal interosseous muscle during and immediately following a submaximal fatiguing contraction, and after rest. Coherence between composite MU spike trains, derived from decomposed surface EMG, were examined in the delta (14 Hz), alpha (812 Hz), beta (1530 Hz), and gamma (3060 Hz) frequency band ranges. A significant increase in MU coherence was observed in the delta, alpha, and beta frequency bands postfatigue. In addition, wavelet coherence revealed a tendency for delta-, alpha-, and beta-band coherence to increase during the fatiguing contraction, with subjects exhibiting low initial coherence values displaying the greatest relative increase. This was accompanied by an increase in MU short-term synchronization and a decline in mean firing rate of the majority of MUs detected during the sustained contraction. A model of the motoneuron pool and surface EMG was used to investigate factors influencing the coherence estimate. Simulation results indicated that changes in motoneuron inhibition and firing rates alone could not directly account for increased beta-band coherence postfatigue. The observed increase is, therefore, more likely to arise from an increase in the strength of correlated inputs to MUs as the muscle fatigues.439Scopus© Citations 48 - PublicationAnalysis of the Effects of Mechanically Induced tremor on EEG-EMG Coherence Using Wavelet and Partial Directed Coherence(IEEE, 2013-11-08)
; ; ; ; ; Corticomuscular coherence between human cortical rhythms and surface electromyography (sEMG) is commonly observed within the beta (13-35 Hz) and gamma (35-60 Hz) band frequency ranges, but is typically absent within the alpha band (8-12 Hz) in healthy subjects. A recent study has shown that significant alpha band corticomuscular coherence can be mechanically induced in healthy subjects using a spring of appropriate stiffness. Traditional coherence analysis is limited to examining whether a correlation exists between the electroencephalograph (EEG) and EMG recordings, by portraying instances of mutual synchrony. In this study the temporal evolution and directionality of the interaction between the EEG and EMG signals during mechanically induced alpha band coherence were investigated using two recent extensions of classical coherence, wavelet analysis and partial directed coherence. The results indicate a significant increase in directional information flow within the alpha and piper band frequency ranges in the EMG to EEG direction, and appear to provide evidence of the contribution of afferent feedback, and to a lesser extent descending cortical drives, to alpha band corticomuscular coherence.606Scopus© Citations 6 - PublicationFeature-Based Evaluation of a Wearable Surface EMG Sensor against Laboratory Standard EMG during Force-Varying and Fatiguing Contractions(IEEE, 2020-03)
; ; ; ; Recent advances in wearable sensors enable recording of electromyography (EMG) outside the laboratory for extended periods of time. However, the properties of wearable EMG systems designed for long-term recording may differ from those of laboratory-standard systems, potentially impacting data. This study evaluated EMG features derived from signals recorded using a wearable system (BioStampRC, MC10 Inc.) against a reference laboratory system (Bagnoli, Delsys Inc.). Surface EMG data from the biceps brachii were recorded simultaneously using both systems during isometric elbow flexion, between 10% and 80% of maximum voluntary contraction (MVC), and during sustained submaximal fatiguing contraction, in twelve subjects. Linear and nonlinear EMG temporal and spectral features were then compared across both systems. No effect of recording system was detected on EMG onset/offset times, or on the relationship between force and EMG root mean squared amplitude. However, the relationships between force and median frequency, percentage determinism and multiscale entropy differed between systems. Baseline noise was also greater for the BioStampRC. Lower median frequencies were observed for the wearable system, likely due to the larger interelectrode distance, however, the relative change in EMG amplitude and median frequency during the fatiguing contraction was similar for both. Percentage determinism increased and multiscale entropy decreased during the fatiguing contraction for both systems, with higher and lower values respectively for the wearable system. Results indicate that the BiostampRC is appropriate for EMG onset/offset and amplitude estimation. However, caution is advised when comparing across systems as spectral and nonlinear features may differ due to electrode design differences.Scopus© Citations 28 43 - PublicationBeta-band Motor Unit Coherence and Nonlinear Surface EMG Features of the First Dorsal Interosseous Muscle Vary with Force(American Physiological Society, 2019-09)
; ; Motor unit (MU) firing times are weakly coupled across a range of frequencies during voluntary contractions. Coherent activity within the beta-band (15-35 Hz) has been linked to oscillatory cortical processes, providing evidence of functional connectivity between the motoneuron pool and motor cortex. The aim of this study was to investigate whether beta-band MU coherence is altered with increasing abduction force in the first dorsal interosseous muscle. Coherence between MU firing times, extracted from decomposed surface EMG signals, was investigated in 17 subjects at 10%, 20%, 30% and 40% of maximum voluntary contraction. Corresponding changes in nonlinear surface EMG features, specifically sample entropy and determinism which are sensitive to MU synchronization, were also examined. A reduction in beta-band and alpha-band coherence was observed as force increased (F(3, 151) = 32, p < .001 and F(3, 151) = 27, p < .001, respectively), accompanied by corresponding changes in nonlinear surface EMG features. A significant relationship between the nonlinear features and MU coherence was also detected (r = -0.43 ± 0.1 and r = 0.45 ± 0.1, for sample entropy and determinism, respectively, both p < .001). The reduction in beta-band coherence suggests a change in the relative contribution of correlated and uncorrelated pre-synaptic inputs to the motoneuron pool, and/or a decrease in the responsiveness of the motoneuron pool to synchronous inputs at higher forces. The study highlights the importance of considering muscle activation when investigating changes in MU coherence or nonlinear EMG features, and examines other factors that can influence coherence estimation.446Scopus© Citations 14 - PublicationInvestigating the Effect of Persistent Inward Currents on Motor Unit Firing Rates and Beta-Band Coherence in a Model of the First Dorsal Interosseous MuscleNeuromodulatory drive resulting in the generation of persistent inward currents (PICs) within motoneuron dendrites has been demonstrated to introduce nonlinearities into the motoneuron input-output function for a given motor command. It is less understood, however, as to what role PICs play during voluntary contractions or on the correlation between motoneuron firings arising as a result of common synaptic inputs to the motoneuron pool. To examine this, a biophysical model of the motoneuron pool representing the first dorsal interosseous (FDI) muscle was used to simulate the effects of PICs on motor unit firing patterns and beta-band (15-30 Hz) motor unit coherence at 20, 30, and 40 percent of maximum voluntary contraction (MVC). The contribution of PICs at each MVC was quantified by calculating the difference in the mean firing rate of each motoneuron within the pool and assessing changes in the mean firing rate distribution and motor unit coherence with and without PICs present. The results of the current study demonstrated that increased activation of PICs progressively reduced motor unit coherence, however, changes in coherence were modest when investigating activation levels consistent with experimentally observed mean motor unit firing rates in the FDI muscle during isometric voluntary contraction.
448Scopus© Citations 2