scholarly journals Preceding muscle activity influences motor unit discharge and rate of torque development during ballistic contractions in humans

2005 ◽  
Vol 562 (2) ◽  
pp. 635-644 ◽  
Author(s):  
Michaël Van Cutsem ◽  
Jacques Duchateau
Keyword(s):  
Motor Unit ◽  
Muscle Activity ◽  
Unit Discharge ◽  
Rate Of Torque Development ◽  
Motor Unit Discharge ◽  
Torque Development

Blockade of 5-HT2 receptors suppresses rate of torque development and motor unit discharge rate during rapid contractions

2021 ◽  
Author(s):  
Benjamin Ian Goodlich ◽  
Sean A Horan ◽  
Justin J Kavanagh
Keyword(s):  
Motor Unit ◽  
Unit Activity ◽  
Repeated Measures ◽  
Discharge Rate ◽  
Voluntary Contraction ◽  
Unit Discharge ◽  
Motor Unit Activity ◽  
Rate Of Torque Development ◽  
Motor Unit Discharge ◽  
Torque Development

Serotonin (5-HT) is a neuromodulator that is critical for regulating the excitability of spinal motoneurons and the generation of muscle torque. However, the role of 5-HT in modulating human motor unit activity during rapid contractions has yet to be assessed. Nine healthy participants (23.7 ± 2.2 yr) ingested 8 mg of the competitive 5-HT2 antagonist cyproheptadine in a double-blinded, placebo-controlled, repeated-measures experiment. Rapid dorsiflexion contractions were performed at 30%, 50% and 70% of maximal voluntary contraction (MVC), where motor unit activity was assessed by high-density surface electromyographic decomposition. A second protocol was performed where a sustained, fatigue-inducing dorsiflexion contraction was completed prior to undertaking the same 30%, 50% and 70% MVC rapid contractions and motor unit analysis. Motor unit discharge rate (p < 0.001) and rate of torque development (RTD; p = 0.019) for the unfatigued muscle were both significantly lower for the cyproheptadine condition. Following the fatigue inducing contraction, cyproheptadine reduced motor unit discharge rate (p < 0.001) and RTD (p = 0.024), where the effects of cyproheptadine on motor unit discharge rate and RTD increased with increasing contraction intensity. Overall, these results support the viewpoint that serotonergic effects in the central nervous system occur fast enough to regulate motor unit discharge rate during rapid powerful contractions.

Age-related decline in rate of torque development is accompanied by lower maximal motor unit discharge frequency during fast contractions

2008 ◽  
Vol 104 (3) ◽  
pp. 739-746 ◽  
Author(s):  
Malgorzata Klass ◽  
Stéphane Baudry ◽  
Jacques Duchateau
Keyword(s):  
Motor Unit ◽  
Discharge Frequency ◽  
Maximal Rate ◽  
Unit Discharge ◽  
Rate Of Torque Development ◽  
Age Related ◽  
Motor Unit Discharge ◽  
Integrated Emg ◽  
Voluntary Contractions ◽  
Torque Development

The aim of this study was to investigate the association between the rate of torque development and maximal motor unit discharge frequency in young and elderly adults as they performed rapid submaximal contractions with the ankle dorsiflexors. Recordings were obtained of the torque exerted by the dorsiflexors during the isometric contractions and the surface and intramuscular electromyograms (EMGs) from the tibialis anterior. The maximal rate of torque development and integrated EMG (percentage of total EMG burst) at peak rate of torque development during fast contractions were lower in elderly than young adults by 48% ( P < 0.05) and 16.5% ( P < 0.05), respectively. The young adults, but not the elderly adults, exhibited a positive association ( r2 = 0.33; P < 0.01) between the integrated EMG computed up to the peak rate of torque development and the maximal rate of torque development achieved during the fast contractions. These age-related changes during fast voluntary contractions were accompanied by a decline ( P < 0.001) in motor unit discharge frequency (19, 28, and 34% for first 3 interspike intervals, respectively) and in the percentage of units (45%; P < 0.05) that exhibited double discharges (doublets) at brief intervals (<5 ms). Because aging decreased the maximal rate of torque development of fast voluntary contractions to a greater extent (∼10%) than that of an electrically evoked twitch, collectively the results indicate that the age-related decline in maximal motor unit discharge frequency likely limit, in addition to the slowing of muscle contractile properties, the performance of fast voluntary contractions.

Frequency Modulation of Motor Unit Discharge Has Task-Dependent Effects on Fluctuations in Motor Output

2005 ◽  
Vol 94 (4) ◽  
pp. 2878-2887 ◽  
Author(s):  
Carol J. Mottram ◽  
Evangelos A. Christou ◽  
François G. Meyer ◽  
Roger M. Enoka
Keyword(s):  
Motor Unit ◽  
Frequency Modulation ◽  
Discharge Rate ◽  
Motor Output ◽  
Unit Discharge ◽  
Rate Of Increase ◽  
Output Force ◽  
Position Task ◽  
Motor Unit Discharge ◽  
Target Force

The rate of change in the fluctuations in motor output differs during the performance of fatiguing contractions that involve different types of loads. The purpose of this study was to examine the contribution of frequency modulation of motor unit discharge to the fluctuations in the motor output during sustained contractions with the force and position tasks. In separate tests with the upper arm vertical and the elbow flexed to 1.57 rad, the seated subjects maintained either a constant upward force at the wrist (force task) or a constant elbow angle (position task). The force and position tasks were performed in random order at a target force equal to 3.6 ± 2.1% (mean ± SD) of the maximal voluntary contraction (MVC) force above the recruitment threshold of an isolated motor unit from the biceps brachii. Each subject maintained the two tasks for an identical duration (161 ± 93 s) at a mean target force of 22.4 ± 13.6% MVC. As expected, the rate of increase in the fluctuations in motor output (force task: SD for detrended force; position task: SD for vertical acceleration) was greater for the position task than the force task ( P < 0.001). The amplitude of the coefficient of variation (CV) and the power spectra for motor unit discharge were similar between tasks ( P > 0.1) and did not change with time ( P > 0.1), and could not explain the different rates of increase in motor output fluctuations for the two tasks. Nonetheless, frequency modulation of motor unit discharge differed during the two tasks and predicted ( P < 0.001) both the CV for discharge rate (force task: 1–3, 12–13, and 14–15 Hz; position task: 0–1, and 1–2 Hz) and the fluctuations in motor output (force task: 5–6, 9–10, 12–13, and 14–15 Hz; position task: 6–7, 14–15, 17–19, 20–21, and 23–24 Hz). Frequency modulation of motor unit discharge rate differed for the force and position tasks and influenced the ability to sustain steady contractions.

Low-frequency common modulation of soleus motor unit discharge is enhanced during postural control in humans

2006 ◽  
Vol 175 (4) ◽  
pp. 584-595 ◽  
Author(s):  
G. Mochizuki ◽  
J. G. Semmler ◽  
T. D. Ivanova ◽  
S. J. Garland
Keyword(s):  
Postural Control ◽  
Motor Unit ◽  
Low Frequency ◽  
Unit Discharge ◽  
Motor Unit Discharge

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

Variability of motor unit discharge and force fluctuations across a range of muscle forces in older adults

2005 ◽  
Vol 32 (4) ◽  
pp. 533-540 ◽  
Author(s):  
Brian L. Tracy ◽  
Katrina S. Maluf ◽  
Jennifer L. Stephenson ◽  
Sandra K. Hunter ◽  
Roger M. Enoka
Keyword(s):  
Older Adults ◽  
Motor Unit ◽  
Muscle Forces ◽  
Unit Discharge ◽  
Force Fluctuations ◽  
Motor Unit Discharge
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