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McManus, Lara M.
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McManus, Lara M.
Official Name
McManus, Lara M.
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Now showing 1 - 6 of 6
- 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.144 - 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.166 - PublicationThe Influence of Force Level and Motor Unit Coherence on Nonlinear Surface EMG Features Examined Using Model Simulation(IEEE, 2019-07-27)
; ; ; Nonlinear features extracted from surface EMG signals have been previously used to infer information on coherent or synchronous activity in the underlying motor unit discharges. However, it has not yet been assessed how these features are affected by the density of the surface EMG signal, and whether changes in the level of muscle activation can influence the effective detection of correlated motor unit firing. To examine this, a motoneuron pool model receiving a beta-band modulated cortical input was used to generate correlated motor unit firing trains. These firing trains were convolved with motor unit action potentials generated from an anatomically accurate electrophysiological model of the first dorsal interosseous muscle. The sample entropy (SampEn) and percentage determinism (%DET) of recurrence quantification analysis were calculated from the composite surface EMG signals, for signals comprised of both correlated and uncorrelated motor unit firing trains. The results show that although both SampEn and %DET are influenced by motor unit coherence, they are differentially affected by muscle activation and motor unit distribution. The results also suggest that sample entropy may provide a more accurate assessment of the underlying motor unit coherence than percentage determinism, as it is less sensitive to factors unrelated to motor unit synchrony.380Scopus© Citations 2 - 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.
403Scopus© Citations 2 - 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.570Scopus© Citations 6 - 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.311Scopus© Citations 3