Excitability tests using high-density surface-EMG: A novel approach to studying single motor units

Rectification of surface electromyographic (EMG) recordings prior to their correlation with other signals is a widely used form of preprocessing. Recently this practice has come into question, elevating the subject of EMG rectification to a topic of much debate. Proponents for rectifying suggest it accentuates the EMG spike timing information, whereas opponents indicate it is unnecessary and its nonlinear distortion of data is potentially destructive. Here we examine the necessity of rectification on the extraction of muscle responses, but for the first time using a known oscillatory input to the muscle in the form of electrical vestibular stimulation. Participants were exposed to sinusoidal vestibular stimuli while surface and intramuscular EMG were recorded from the left medial gastrocnemius. We compared the unrectified and rectified surface EMG to single motor units to determine which method best identified stimulus-EMG coherence and phase at the single-motor unit level. Surface EMG modulation at the stimulus frequency was obvious in the unrectified surface EMG. However, this modulation was not identified by the fast Fourier transform, and therefore stimulus coherence with the unrectified EMG signal failed to capture this covariance. Both the rectified surface EMG and single motor units displayed significant coherence over the entire stimulus bandwidth (1–20 Hz). Furthermore, the stimulus-phase relationship for the rectified EMG and motor units shared a moderate correlation ( r = 0.56). These data indicate that rectification of surface EMG is a necessary step to extract EMG envelope modulation due to motor unit entrainment to a known stimulus.

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A high-density multichannel surface electromyography system for the characterization of single motor units

Review of Scientific Instruments ◽

10.1063/1.1455134 ◽

2002 ◽

Vol 73 (4) ◽

pp. 1887-1897 ◽

Cited By ~ 88

Author(s):

J. H. Blok ◽

J. P. van Dijk ◽

G. Drost ◽

M. J. Zwarts ◽

D. F. Stegeman

Keyword(s):

Surface Electromyography ◽

Motor Units ◽

High Density ◽

Single Motor ◽

Single Motor Units

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Progressive FastICA Peel-Off and Convolution Kernel Compensation Demonstrate High Agreement for High Density Surface EMG Decomposition

Neural Plasticity ◽

10.1155/2016/3489540 ◽

2016 ◽

Vol 2016 ◽

pp. 1-5 ◽

Cited By ~ 10

Author(s):

Maoqi Chen ◽

Ales Holobar ◽

Xu Zhang ◽

Ping Zhou

Keyword(s):

Motor Units ◽

Surface Emg ◽

High Density ◽

Convolution Kernel ◽

High Agreement ◽

Density Surface ◽

Processing Techniques ◽

High Degree ◽

Neurologically Intact ◽

Signal Processing Techniques

Decomposition of electromyograms (EMG) is a key approach to investigating motor unit plasticity. Various signal processing techniques have been developed for high density surface EMG decomposition, among which the convolution kernel compensation (CKC) has achieved high decomposition yield with extensive validation. Very recently, a progressive FastICA peel-off (PFP) framework has also been developed for high density surface EMG decomposition. In this study, the CKC and PFP methods were independently applied to decompose the same sets of high density surface EMG signals. Across 91 trials of 64-channel surface EMG signals recorded from the first dorsal interosseous (FDI) muscle of 9 neurologically intact subjects, there were a total of 1477 motor units identified from the two methods, including 969 common motor units. On average,10.6±4.3common motor units were identified from each trial, which showed a very high matching rate of97.85±1.85% in their discharge instants. The high degree of agreement of common motor units from the CKC and the PFP processing provides supportive evidence of the decomposition accuracy for both methods. The different motor units obtained from each method also suggest that combination of the two methods may have the potential to further increase the decomposition yield.

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Topographical Characteristics of Motor Units of the Lower Facial Musculature Revealed by Means of High-Density Surface EMG

Journal of Neurophysiology ◽

10.1152/jn.00265.2005 ◽

2006 ◽

Vol 95 (1) ◽

pp. 342-354 ◽

Cited By ~ 55

Author(s):

Bernd G. Lapatki ◽

Robert Oostenveld ◽

Johannes P. Van Dijk ◽

Irmtrud E. Jonas ◽

Machiel J. Zwarts ◽

...

Keyword(s):

Motor Units ◽

Surface Emg ◽

High Density ◽

Facial Musculature ◽

Density Surface

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Properties of Motor Units of Elbow and Ankle Muscles Decomposed Using High-Density Surface EMG

2019 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC) ◽

10.1109/embc.2019.8857475 ◽

2019 ◽

Cited By ~ 1

Author(s):

Altamash S. Hassan ◽

Edward H. Kim ◽

Obaid U. Khurram ◽

Mark Cummings ◽

Christopher K. Thompson ◽

...

Keyword(s):

Motor Units ◽

Surface Emg ◽

High Density ◽

Ankle Muscles ◽

Density Surface

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Soleus single motor units show stronger coherence with Achilles tendon vibration across a broad bandwidth relative to medial gastrocnemius units while standing

Journal of Neurophysiology ◽

10.1152/jn.00352.2019 ◽

2019 ◽

Vol 122 (5) ◽

pp. 2119-2129 ◽

Cited By ~ 3

Author(s):

Robyn L. Mildren ◽

Ryan M. Peters ◽

Mark G. Carpenter ◽

Jean-Sébastien Blouin ◽

J. Timothy Inglis

Keyword(s):

Achilles Tendon ◽

Phase Locking ◽

Motor Units ◽

Surface Emg ◽

Triceps Surae ◽

Medial Gastrocnemius ◽

Single Motor ◽

Single Motor Units ◽

Cross Covariance ◽

The Relationship

To probe the frequency characteristics of somatosensory responses in the triceps surae muscles, we previously applied suprathreshold noisy vibration to the Achilles tendon and correlated it with ongoing triceps surae muscle activity (recorded via surface EMG) during standing. Stronger responses to tendon stimuli were observed in soleus (Sol) relative to medial gastrocnemius (MGas) surface EMG; however, it is unknown whether differences in motor unit activity or limitations of surface EMG could have influenced this finding. Here, we inserted indwelling EMG into Sol and MGas to record the activity of single motor units while we applied noisy vibration (10–115 Hz) to the right Achilles tendon of standing participants. We analyzed the relationship between vibration acceleration and the spike activity of active single motor units through estimates of coherence, gain, phase, and cross-covariance. We also applied sinusoidal vibration at frequencies from 10 to 100 Hz (in 5-Hz increments) to examine whether motor units demonstrate nonlinear synchronization or phase locking at higher frequencies. Relative to MGas single motor units, Sol units demonstrated stronger coherence and higher gain with noisy vibration across a bandwidth of 7–68 Hz, and larger peak-to-peak cross-covariance at all four stimulus amplitudes examined. Sol and MGas motor unit activity was modulated over the time course of the sinusoidal stimuli across all frequencies, but their phase-locking behavior was minimal. These findings suggest Sol plays a prominent role in responding to disturbances transmitted through the Achilles tendon across a broad frequency band during standing. NEW & NOTEWORTHY We examined the relationship between Achilles tendon stimuli and spike times of single soleus (Sol) and medial gastrocnemius (MGas) motor units during standing. Relative to MGas, Sol units demonstrated stronger coherence and higher gain with noisy stimuli across a bandwidth of 7–68 Hz. Sol and MGas units demonstrated minimal nonlinear phase locking with sinusoidal stimuli. These findings indicate Sol plays a prominent role in responding to tendon stimuli across a broad frequency band.

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An adjoint approach to identification in Electromyography: Modeling and first order optimality conditions

Inverse Problems ◽

10.1088/1361-6420/ac362c ◽

2021 ◽

Author(s):

Tobias Sproll ◽

Anton Schiela

Keyword(s):

Optimality Conditions ◽

Motor Units ◽

Surface Emg ◽

Control Approach ◽

First Order ◽

Single Motor Units ◽

Density Surface ◽

Adjoint Approach ◽

Optimal Control Approach ◽

First Order Optimality Conditions

Abstract In medical treatment, it can be necessary to know the position of a motor unit in a muscle. Recent advances in high-density surface Electromyography (EMG) measurement have opened the possibility of extracting information about single motor units. We present a mathematical approach to identify these motor units. On the base of an electrostatic forward model, we introduce an adjoint approach to eﬃciently simulate a surface EMG measurement and an optimal control approach to identify these motor units. We show basic results on existence of solutions and ﬁrst-order optimality conditions.

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