Adaptations in maximal motor unit discharge rate to strength training in young and older adults

2001 ◽  
Vol 24 (4) ◽  
pp. 542-550 ◽  
Author(s):  
Carolynn Patten ◽  
Gary Kamen ◽  
Daniel M. Rowland
Keyword(s):  
Older Adults ◽  
Strength Training ◽  
Motor Unit ◽  
Discharge Rate ◽  
Unit Discharge ◽  
Motor Unit Discharge

Fluctuations in Isometric Force Are Associated With Motor Unit Discharge Rate Variability in Older Adults

2004 ◽  
Vol 36 (Supplement) ◽  
pp. S123 ◽  
Author(s):  
Jennifer L. Stephenson ◽  
Katrina S. Maluf ◽  
Brian L. Tracy ◽  
Sandra K. Hunter ◽  
Roger M. Enoka
Keyword(s):  
Older Adults ◽  
Motor Unit ◽  
Isometric Force ◽  
Discharge Rate ◽  
Unit Discharge ◽  
Motor Unit Discharge

Motor unit discharge behavior in older adults during maximal-effort contractions

1995 ◽  
Vol 79 (6) ◽  
pp. 1908-1913 ◽  
Author(s):  
G. Kamen ◽  
S. V. Sison ◽  
C. C. Du ◽  
C. Patten
Keyword(s):  
Older Adults ◽  
Motor Unit ◽  
Discharge Rate ◽  
Force Production ◽  
Motor Units ◽  
Older Individuals ◽  
Unit Discharge ◽  
Maximal Force ◽  
Motor Unit Discharge ◽  
Common Observation

A reduction in maximal force production is a common observation in older individuals. In an effort to determine whether aging is accompanied by reductions in central motoneuron drive limiting motor performance, motor unit discharge records were obtained from seven young (21–33 yr) and seven older (> 67 yr) adults. Informed consent was obtained from all subjects. The task required the subject to perform a maximal abduction of the second digit under isometric conditions. Motor unit potentials in the first dorsal interosseous were monitored by using a selective four-wire needle electrode and identified off-line with the aid of a Dantec electromyograph. The maximal discharge rate in the older adults (31.1 impulses/s) was significantly smaller (P < 0.05) than that in the younger subjects (50.9 impulses/s). These findings suggest that reductions in maximal force capability in older adults are partially due to an impaired ability to fully drive the surviving motor units.

Fluctuations in Isometric Force Are Associated With Motor Unit Discharge Rate Variability in Older Adults

2004 ◽  
Vol 36 (Supplement) ◽  
pp. S123
Author(s):  
Jennifer L. Stephenson ◽  
Katrina S. Maluf ◽  
Brian L. Tracy ◽  
Sandra K. Hunter ◽  
Roger M. Enoka
Keyword(s):  
Older Adults ◽  
Motor Unit ◽  
Isometric Force ◽  
Discharge Rate ◽  
Unit Discharge ◽  
Motor Unit Discharge

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.

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.

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

Reduced knee-extensor torque steadiness and higher motor unit discharge rate variability in individuals with patellofemoral pain

Physiotherapy ◽  
2019 ◽  
Vol 105 ◽  
pp. e46
Author(s):  
E. Martinez-Valdes ◽  
G. Boccia ◽  
M. Nawaz ◽  
F. Negro ◽  
A. Rainoldi ◽  
...  
Keyword(s):  
Motor Unit ◽  
Discharge Rate ◽  
Knee Extensor ◽  
Patellofemoral Pain ◽  
Unit Discharge ◽  
Motor Unit Discharge ◽  
Extensor Torque
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