Discharge Patterns of Motor Units during Cat Locomotion and Their Relation to Muscle Performance

1976 ◽  
pp. 789-793 ◽  
Author(s):  
F. E. Zajac ◽  
J. L. Young
Keyword(s):  
Motor Units ◽  
Muscle Performance ◽  
Discharge Patterns

Effects of activation pattern on nonisometric human skeletal muscle performance

2007 ◽  
Vol 102 (5) ◽  
pp. 1985-1991 ◽  
Author(s):  
Ryan D. Maladen ◽  
Ramu Perumal ◽  
Anthony S. Wexler ◽  
Stuart A. Binder-Macleod
Keyword(s):  
Skeletal Muscle ◽  
Instantaneous Frequency ◽  
Muscle Activation ◽  
Motor Units ◽  
Muscle Performance ◽  
Variable Frequency ◽  
Constant Frequency ◽  
Muscle Activation Patterns ◽  
Activation Rate ◽  
Discharge Patterns

During volitional muscle activation, motor units often fire with varying discharge patterns that include brief, high-frequency bursts of activity. These variations in the activation rate allow the central nervous system to precisely control the forces produced by the muscle. The present study explores how varying the instantaneous frequency of stimulation pulses within a train affects nonisometric muscle performance. The peak excursion produced in response to each stimulation train was considered as the primary measure of muscle performance. The results showed that at each frequency tested between 10 and 50 Hz, variable-frequency trains that took advantage of the catchlike property of skeletal muscle produced greater excursions than constant-frequency trains. In addition, variable-frequency trains that could achieve targeted trajectories with fewer pulses than constant-frequency trains were identified. These findings suggest that similar to voluntary muscle activation patterns, varying the instantaneous frequency within a train of pulses can be used to improve muscle performance during functional electrical stimulation.

Discharge patterns in human motor units during fatiguing arm movements

1998 ◽  
Vol 85 (5) ◽  
pp. 1684-1692 ◽  
Author(s):  
L. Griffin ◽  
S. J. Garland ◽  
T. Ivanova
Keyword(s):  
Voluntary Movement ◽  
Motor Units ◽  
Constant Load ◽  
Short Isis ◽  
Interspike Intervals ◽  
Triceps Brachii ◽  
Movement Initiation ◽  
Human Motor ◽  
Discharge Patterns ◽  
Human Motor Units

The purpose of this study was to determine whether short interspike intervals (ISIs of <20 ms) would occur naturally during voluntary movement and would increase in number with fatigue. Thirty-four triceps brachii motor units from nine subjects were assessed during a fatigue task consisting of fifty extension and fifty flexion elbow movements against a constant-load opposing extension. Nineteen motor units were recorded from the beginning of the fatigue task; the number of short ISIs was 7.1 ± 4.1% of the total number of ISIs in the first one-third of the task (unfatigued state). This value increased to 11.8 ± 5.9% for the last one-third of the task (fatigued state). Fifteen motor units were recruited during the fatigue task and discharged, with 16.4 ± 6.0% of short ISIs in the fatigued state. For all motor units, the number of short ISIs was positively correlated ( r 2 = 0.85) with the recruitment threshold torque. Short ISIs occurred most frequently at movement initiation but also occurred throughout the movement. These results document the presence of short ISIs during voluntary movement and their increase in number during fatigue.

Sleep/Wake Firing Patterns of Human Genioglossus Motor Units

2007 ◽  
Vol 98 (6) ◽  
pp. 3284-3291 ◽  
Author(s):  
E. Fiona Bailey ◽  
Keith W. Fridel ◽  
Amber D. Rice
Keyword(s):  
Temporal Relationship ◽  
Motor Units ◽  
Nrem Sleep ◽  
Future Research ◽  
Mechanical Environment ◽  
Firing Patterns ◽  
Obstructive Sleep ◽  
Respiratory Modulation ◽  
Discharge Patterns ◽  
Whole Muscle

Although studies of the principal tongue protrudor muscle genioglossus (GG) suggest that whole muscle GG electromyographic (EMG) activities are preserved in nonrapid eye movement (NREM) sleep, it is unclear what influence sleep exerts on individual GG motor unit (MU) activities. We characterized the firing patterns of human GG MUs in wakefulness and NREM sleep with the aim of determining 1) whether the range of MU discharge patterns evident in wakefulness is preserved in sleep and 2) what effect the removal of the “wakefulness” input has on the magnitude of the respiratory modulation of MU activities. Microelectrodes inserted into the extrinsic tongue protrudor muscle, the genioglossus, were used to follow the discharge of single MUs. We categorized MU activities on the basis of the temporal relationship between the spike train and the respiration cycle and quantified the magnitude of the respiratory modulation of each MU using the eta (η2) index, in wakefulness and sleep. The majority of MUs exhibited subtle increases or decreases in respiratory modulation but were otherwise unaffected by NREM sleep. In contrast, 30% of MUs exhibited marked sleep-associated changes in discharge frequency and respiratory modulation. We suggest that GG MUs should not be considered exclusively tonic or phasic; rather, the discharge pattern appears to be a flexible feature of GG activities in healthy young adults. Whether such flexibility is important in the response to changes in the chemical and/or mechanical environment and whether it is preserved as a function of aging or in individuals with obstructive sleep apnea are critical questions for future research.

scholarly journals Discharge Patterns of Human Genioglossus Motor Units during Arousal from Sleep

SLEEP ◽  
2010 ◽  
Vol 33 (3) ◽  
pp. 379-387 ◽  
Author(s):  
Vanessa Wilkinson ◽  
Atul Malhotra ◽  
Christian L. Nicholas ◽  
Christopher Worsnop ◽  
Amy S. Jordan ◽  
...  
Keyword(s):  
Motor Units ◽  
Discharge Patterns

scholarly journals Influence of duty cycle on the time course of muscle fatigue and the onset of neuromuscular compensation during exhaustive dynamic isolated limb exercise

2015 ◽  
Vol 309 (1) ◽  
pp. R51-R61 ◽  
Author(s):  
Christopher W. Sundberg ◽  
Matthew W. Bundle
Keyword(s):  
Muscle Fatigue ◽  
Duty Cycle ◽  
Time Course ◽  
Anaerobic Metabolism ◽  
Motor Units ◽  
Knee Extension ◽  
Muscle Performance ◽  
Absolute Level ◽  
Performance Loss ◽  
Knee Extension Exercise

We investigated the influence of altered muscle duty cycle on the performance decrements and neuromuscular responses occurring during constant-load, fatiguing bouts of knee extension exercise. We experimentally altered the durations of the muscularly inactive portion of the limb movement cycle and hypothesized that greater relative durations of inactivity within the same movement task would 1) reduce the rates and extent of muscle performance loss and 2) increase the forces necessary to trigger muscle fatigue. In each condition (duty cycle = 0.6 and 0.3), male subjects [age = 25.9 ± 2.0 yr (SE); mass = 85.4 ± 2.6 kg], completed 9–11 exhaustive bouts of two-legged knee extension exercise, at force outputs that elicited failure between 4 and 290 s. The novel duty cycle manipulation produced two primary results; first, we observed twofold differences in both the extent of muscle performance lost (DC0.6 = 761 ± 35 N vs. DC0.3 = 366 ± 49 N) and the time course of performance loss. For example, exhaustive trials at the midpoint of these force ranges differed in duration by more than 30 s ( t0.6 = 36 ± 2.6 vs. t0.3 = 67 ± 4.3 s). Second, both the minimum forces necessary to exceed the peak aerobic capacity and initiate a reliance on anaerobic metabolism, and the forces necessary to elicit compensatory increases in electromyogram activity were 300% greater in the lower vs. higher duty cycle condition. These results indicate that the fatigue-induced compensatory behavior to recruit additional motor units is triggered by a reliance on anaerobic metabolism for ATP resynthesis and is independent of the absolute level or fraction of the maximum force produced by the muscle.

Recruitment and Discharge Patterns of Single Motor Units During Speech Production

1977 ◽  
Vol 20 (4) ◽  
pp. 613-630 ◽  
Author(s):  
Harvey M. Sussman ◽  
Peter F. MacNeilage ◽  
Randall K. Powers
Keyword(s):  
Dynamic Range ◽  
Isometric Force ◽  
Discharge Rate ◽  
Motor Units ◽  
Size Principle ◽  
Single Motor ◽  
Single Motor Units ◽  
Movement Dynamics ◽  
Discharge Patterns ◽  
Anterior Belly

Recruitment and discharge patterns of single motor units (MUs) in the anterior belly of digastric were studied during speech in three subjects, using electrodes facilitating selective recording at high force levels. Fixed recruitment order was observed in over 99% of all comparisons. Later recruited units invariably possessed muscle action potentials of higher amplitude, suggesting that units were activated in accordance with the “size principle.” Additional evidence for this was that later recruited units, of a set of three studied during speech, motor unit training, and isometric force ramps, showed greater sensitivity to input, and greater dynamic range than earlier recruited units. Units in this set were much more sensitive to rapid changes in input associated with speech gestures than to static activation even at high force levels. Several significant relations between discharge characteristics and aspects of movement dynamics were observed, including relations between (1) recruitment interval (MU1 to MU3) and latency of mandibular lowering, (2) onset of initial discharge of MU1 and relative mechanical advantage of the mandible, (3) number of MUs active and velocity and displacement of the mandible, and (4) discharge rate of MU3 and velocity and displacement of the mandible.

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