Motor unit differentiation and integrated surface EMG in voluntary isometric contraction

1976 ◽  
Vol 35 (2) ◽  
pp. 149-157 ◽  
Author(s):  
B. Maton
Keyword(s):  
Motor Unit ◽  
Isometric Contraction ◽  
Surface Emg

scholarly journals Rotation of Motoneurons During Prolonged Isometric Contractions in Humans

2006 ◽  
Vol 96 (3) ◽  
pp. 1135-1140 ◽  
Author(s):  
Parveen Bawa ◽  
Marco Y. Pang ◽  
Kari A. Olesen ◽  
Blair Calancie
Keyword(s):  
Motor Unit ◽  
Isometric Contraction ◽  
Motor Units ◽  
Surface Emg ◽  
Neuromuscular Fatigue ◽  
Isometric Contractions ◽  
Muscle Type ◽  
Rotation Surface ◽  
Metabolic Recovery ◽  
The Subject

Prolonged and weak isometric contractions can result in neuromuscular fatigue. Alternation of discharge of motor units with similar thresholds (termed rotation) could be useful to minimize neuromuscular fatigue by providing periods for metabolic recovery of the contractile elements. In the present study, we investigated the prevalence of motoneuron rotation during prolonged contractions of distal limb muscles. Electromyographic (EMG; needle and surface) was recorded from muscles of the forearm and distal leg. The subject made a slowly increasing isometric contraction to recruit and discharge a motor unit ( 1) for a prolonged period of time (>30 min). Sometimes an additional motor unit ( 2) was recruited in which case the subject relaxed the contraction slightly so that only one motor unit remained tonic. Often it was this newly recruited motor unit (i.e., unit 2) that continued discharging, while motor unit 1 fell silent. Continued contraction would then lead to the resumption of tonic discharge of unit 1 and silence of unit 2. This would complete a rotation between motor units 1 and 2. During prolonged contractions, rotation was observed in ∼80% of the motor-unit pairs examined. There was no difference in rotation incidence by muscle type. For the unit pairs showing rotation, surface EMG values were significantly higher immediately prior to rotation than after rotation had occurred. Our findings show that rotation of motor units with similar recruitment thresholds during such contractions is common in distal muscles of the arm and leg and may help offset neuromuscular fatigue.

Amplitude cancellation reduces the size of motor unit potentials averaged from the surface EMG

2006 ◽  
Vol 100 (6) ◽  
pp. 1928-1937 ◽  
Author(s):  
Kevin G. Keenan ◽  
Dario Farina ◽  
Roberto Merletti ◽  
Roger M. Enoka
Keyword(s):  
Motor Unit ◽  
Conduction Velocity ◽  
Motor Units ◽  
Surface Emg ◽  
Excitation Level ◽  
Bipolar Electrode ◽  
Emg Signal ◽  
Motor Unit Synchronization ◽  
Rate Coding ◽  
Simulated Surface

The purpose of the study was to evaluate the influence of selected physiological parameters on amplitude cancellation in the simulated surface electromyogram (EMG) and the consequences for spike-triggered averages of motor unit potentials derived from the interference and rectified EMG signals. The surface EMG was simulated from prescribed recruitment and rate coding characteristics of a motor unit population. The potentials of the motor units were detected on the skin over a hand muscle with a bipolar electrode configuration. Averages derived from the EMG signal were generated using the discharge times for each of the 24 motor units with lowest recruitment thresholds from a population of 120 across three conditions: 1) excitation level; 2) motor unit conduction velocity; and 3) motor unit synchronization. The area of the surface-detected potential was compared with potentials averaged from the interference, rectified, and no-cancellation EMGs. The no-cancellation EMG comprised motor unit potentials that were rectified before they were summed, thereby preventing cancellation between the opposite phases of the potentials. The percent decrease in area of potentials extracted from the rectified EMG was linearly related to the amount of amplitude cancellation in the interference EMG signal, with the amount of cancellation influenced by variation in excitation level and motor unit conduction velocity. Motor unit synchronization increased potentials derived from both the rectified and interference EMG signals, although cancellation limited the increase in area for both potentials. These findings document the influence of amplitude cancellation on motor unit potentials averaged from the surface EMG and the consequences for using the procedure to characterize motor unit properties.

Rectification is required to extract oscillatory envelope modulation from surface electromyographic signals

2014 ◽  
Vol 112 (7) ◽  
pp. 1685-1691 ◽  
Author(s):  
Christopher J. Dakin ◽  
Brian H. Dalton ◽  
Billy L. Luu ◽  
Jean-Sébastien Blouin
Keyword(s):  
Motor Unit ◽  
Stimulus Frequency ◽  
Motor Units ◽  
Surface Emg ◽  
Medial Gastrocnemius ◽  
Single Motor Unit ◽  
Single Motor ◽  
Single Motor Units ◽  
Emg Signal ◽  
Envelope Modulation

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.

SHORT-TERM SYNCHRONY OF MOTOR UNIT DISCHARGE DURING WEAK ISOMETRIC CONTRACTION IN PARKINSON'S DISEASE

Brain ◽  
1992 ◽  
Vol 115 (1) ◽  
pp. 137-154 ◽  
Author(s):  
J. R. BAKER ◽  
N. J. DAVEY ◽  
P. H. ELLAWAY ◽  
C. L. FRIEDILAND
Keyword(s):  
Parkinson’S Disease ◽  
Parkinson's Disease ◽  
Motor Unit ◽  
Isometric Contraction ◽  
Short Term ◽  
Unit Discharge ◽  
Motor Unit Discharge

Contraction-induced potentiation of human motor unit discharge and surface EMG activity

1988 ◽  
Vol 20 (4) ◽  
pp. 391-395 ◽  
Author(s):  
SHUJI SUZUKI ◽  
KOJI KAIYA ◽  
SHIROH WATANABE ◽  
ROBERT S. HUTTON
Keyword(s):  
Motor Unit ◽  
Surface Emg ◽  
Emg Activity ◽  
Unit Discharge ◽  
Motor Unit Discharge ◽  
Human Motor

Motor unit firing rates during constant isometric contraction: establishing and comparing an age-related pattern among muscles

2021 ◽  
Author(s):  
Eric A. Kirk ◽  
Anita D. Christie ◽  
Christopher A. Knight ◽  
Charles L. Rice
Keyword(s):  
Older Adults ◽  
Motor Unit ◽  
Isometric Contraction ◽  
Voluntary Contraction ◽  
Age Related ◽  
Motor Unit Firing ◽  
Euclidean Distances ◽  
Intramuscular Electromyography ◽  
Related Pattern ◽  
Variance Explained

Motor unit (MU) firing rate (FR) frequency is lower in aged adults, compared with young, at relative voluntary contraction intensities. However, from a variety of independent studies of disparate muscles, the age-related degree of difference in FR among muscles is unclear. Using a standardized statistical approach with data derived from primary studies, we quantified differences in FRs across several muscles between younger and older adults. The dataset included 12 different muscles in young (18-35) and older adults (62-93 years) from 18 published and one unpublished study. Experiments recorded single MU activity from intramuscular electromyography during constant isometric contraction at different (step-like) voluntary intensities. For each muscle, FR ranges and FR variance explained by voluntary contraction intensity were determined using bootstrapping. Dissimilarity of FR variance among muscles was calculated by Euclidean distances. There were 3-fold differences in the absolute frequency of FR ranges across muscles in the young (soleus 8-16 and superior trapezius 20-49 Hz), but in the old, FR ranges were more similar and lower for 9 out of 12 muscles. In contrast, the explained FR variance from voluntary contraction intensity in the older group had 1.6-fold greater dissimilarity among muscles than the young (p < 0.001), with FR variance differences being muscle dependent. Therefore, differences between muscle FR ranges were not explained by how FRs scale to changes in voluntary contraction intensity within each muscle. Instead, FRs were muscle dependent but were more dissimilar among muscles in the older group in their responsiveness to voluntary contraction intensity.

The reliability of surface EMG derived motor unit variables

2020 ◽  
Vol 52 ◽  
pp. 102419
Author(s):  
Thomas Hoshizaki ◽  
Edward A. Clancy ◽  
David A. Gabriel ◽  
Lara A. Green
Keyword(s):  
Motor Unit ◽  
Surface Emg
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