Effects of experimental muscle pain on mechanical properties of single motor units in human masseter

1. The effect of age on the motor output of the first dorsal interosseous muscle of 22 (6 female, 16 male) human subjects was investigated. The purpose of the study was to determine the effect of age on the control of muscle force and the associated changes in the discharge behavior and mechanical properties of single motor units. 2. Each subject performed three tasks requiring isometric abduction of the left index finger: a maximum voluntary contraction (MVC), a constant-force task, and a threshold task. The ability to control force was assessed during the constant-force task by quantifying the variation in isometric force about four submaximal target forces (5, 20, 35, and 50% MVC). The threshold task involved sustaining the discharge of the isolated motor unit at a low, steady rate for approximately 3 min. 3. The discharge behavior and the mechanical properties of single motor units were determined during the threshold task by measuring the interimpulse intervals and the peak amplitude and time to peak of the spike-triggered average force. 4. The data indicated that age had an effect on the variation of force about submaximal target forces (range: 5-50% MVC), and that these force variations, when calculated relative to the target force, were greater at lower force levels in the elderly subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

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Spike train characteristics of single motor units in the human masseter muscle

Experimental Neurology ◽

10.1016/0014-4886(78)90026-2 ◽

1978 ◽

Vol 61 (3) ◽

pp. 592-608 ◽

Cited By ~ 26

Author(s):

Bess Derfler ◽

Louis J. Goldberg

Keyword(s):

Spike Train ◽

Masseter Muscle ◽

Motor Units ◽

Single Motor ◽

Single Motor Units

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

Journal of Neurophysiology ◽

10.1152/jn.00296.2014 ◽

2014 ◽

Vol 112 (7) ◽

pp. 1685-1691 ◽

Cited By ~ 19

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.

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