A comparison of electromyographic and mechanical fatigue properties in motor units of the cat hindlimb

Clamann, H. P.; Robinson, Alayna

doi:10.1016/0006-8993(85)91514-8

Cited by 55 publications

(50 citation statements)

References 44 publications

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“…However, as has been noted by Clamann & Robinson (1985), the failure of action potential propagation within progressively larger groups of individual muscle fibres would appear unlikely. Microelectrode studies suggest that a failure of neuromuscular transmission is unlikely to be responsible, since the endplates within large motor units may actually have an increased safety margin of neuromuscular transmission (Grinnell & Trussell, 1983); furthermore, no depletion of transmitter occurs even during high frequencies of nerve stimulation (Krnjevic & Miledi, 1958).…”

Section: High-frequency Failurementioning

confidence: 98%

Motor units within the normal rat medial gastrocnemius

Einsiedel¹,

Luff²

1993

Experimental Physiology

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Section: High-frequency Failurementioning

confidence: 98%

Motor units within the normal rat medial gastrocnemius

Einsiedel¹,

Luff²

1993

Experimental Physiology

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“…44 For instance, using electromyography (EMG), neuromuscular junctions of fast-twitch fatigable motor units (IIx or IIb) were shown to be more susceptible to failure than those of slow-twitch (I) or fast-twitch fatigue-resistant (IIa) motor units. 6,34 However, EMG differences across muscle types may certainly reflect factors other than differences in neuromuscular transmission. Using an alternative approach, Sieck and colleagues demonstrated differences in the depletion of glycogen stores across fiber types with varying levels of activation, reflecting differences in overall muscle use during repeated nerve stimulation.…”

mentioning

confidence: 99%

Synaptic vesicle cycling at type‐identified diaphragm neuromuscular junctions

et al. 2004

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Differences in neuromuscular transmission and neuromuscular junction morphology exist across muscle fiber types. We hypothesized that these fiber-type differences are reflected in the size of the cycling synaptic vesicle pool. Synaptic vesicle cycling at type-identified rat diaphragm neuromuscular junctions was examined by fluorescently labeling presynaptic vesicles with FM4-64. We found that FM4-64 fluorescence uptake was higher at presynaptic terminals of type I/IIa fibers than type IIx/IIb fibers. However, no fiber-type differences in the rate of FM4-64 destaining were found with repetitive nerve stimulation. Synaptic vesicle density at active zones was examined by transmission electron microscopy. In accordance with FM4-64 uptake, synaptic vesicle density was greater at type I/IIa than IIx/IIb fibers. These results demonstrate differences in synaptic vesicle cycling across diaphragm muscle fiber types, which may underlie previously observed differences in neuromuscular transmission across diaphragm muscle fiber types. In the diaphragm, motor units comprising type I and type IIa fibers are most frequently recruited with a duty cycle of approximately 40%. Motor units comprising IIx/IIb fibers are infrequently recruited and only for short durations. The capacity for synaptic vesicle release and cycling at different muscle fiber types matches the functional requirements of these motor units. If the demand for recruitment of motor units comprising IIx/IIb fibers increases, for example, with mechanical loading, there is an increased risk for neuromuscular transmission failure that my relate to the capacity for synaptic vesicle release and cycling. Muscle fiber type-specific adaptations should be considered when examining neuromuscular disorders.

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“…As a result, initial conditions cannot be re-established before the application of a different test. Therefore, the usefulness of results attained by sequential testing is questionable, except possibly for the purpose of motor-unit classification, which is thought to be reliable even after a second fatigue test (Clamann & Robinson, 1985;Botterman & Cope, 1988;Spielmann, 1991). To circumvent the force-recovery problem in the present study, units were subjected to a single fatigue test, using two subtly different stimulus patterns presented in pseudo-random alternation.…”

Section: Potentiated (156%) the Full Ff + Flmentioning

confidence: 99%

The effect of the stimulation pattern on the fatigue of single motor units in adult cats.

Bevan

Laouris

Reinking

et al. 1992

The Journal of Physiology

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SUMMARY1. The main purpose of this study was to examine the effects of two subtly different stimulus patterns on the force developed by fast-twitch, fatiguable motor units in a cat hindlimb muscle during control (pre-fatigue) and fatiguing contractions.2. The peak force and the force-time integral responses of nineteen high fatigue (FF) and three intermediate fatigue (FI) motor units of the tibialis posterior muscle in five deeply anaesthetized adult cats were measured at selected times during the course of a 360-s fatigue test.3. The fatigue test involved a pseudo-random alternation of two patterns of stimulation. One pattern (regular) was composed of a train of stimuli with constant interpulse intervals, set at 1-8 x the twitch contraction time of each unit (interval range, 27-51 ms), and delivered for 500 (or 400) ms. For the total (FF + FI) motorunit sample, the mean (±S.D.) stimulation frequency was 26 + 4 Hz (range, 19-37 Hz). The other stimulus pattern (optimized) consisted of three initial stimuli with short (10 ms) interpulse intervals, followed by a constant interpulse-interval train that was adjusted (interval range, 29-62 ms; frequency, 23 + 5 Hz; frequency range, 16-36 Hz) such that the total train had the same number of pulses, and the same average frequency and duration as the regular train.4. The stimulus trains were delivered at 1 s-5 for 360 s, using three-train sequences of each pattern, randomly alternating with one another. The response of the third train in each sequence was selected for the force measurements. The force profile obtained from the fatigue test was subsequently decomposed into two profiles: one attributable to regular and one to optimized stimulation.5. During the initial responses to the fatigue test, the optimized stimulus pattern produced significantly more force than the regular stimulus pattern. For FF units, the mean increase in peak force (141 %) was significantly greater than the increase in the force-time integral (59 %).6. All motor units exhibited an initial potentiation of peak force with the regular stimulation pattern, whereas peak force declined monotonically with the optimized pattern. In contrast, the force-time integral potentiated in the first 30 s for both regular and optimized stimulus patterns. L. BEVAN AND OTHERS 7. Each motor unit maintained an increased force response to optimized stimulation during the fatigue test, with the greatest relative increase occurring about 120 s into the test, well after the potentiation effect had subsided. At 360 s of stimulation, the force enhancement with optimization was still substantial (83 % for peak force and 37 % for the force-time integral), yet force was virtually non-existent in response to regular stimulation.8. These results suggest that subtle changes in the activation pattern are a potential mechanism by which the central nervous system might increase force during fatigue. Furthermore, force optimization and potentiation seem to be motorunit properties that are as fundamental as the more conventionally stu...

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A comparison of electromyographic and mechanical fatigue properties in motor units of the cat hindlimb

Cited by 55 publications

References 44 publications

Motor units within the normal rat medial gastrocnemius

Motor units within the normal rat medial gastrocnemius

Synaptic vesicle cycling at type‐identified diaphragm neuromuscular junctions

The effect of the stimulation pattern on the fatigue of single motor units in adult cats.

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