Effects of chronic nerve cuff and intramuscular electrodes on rat triceps surae motor units

2001 ◽  
Vol 312 (1) ◽  
pp. 1-4 ◽  
Author(s):  
Jonathan S Carp ◽  
Xiang-Yang Chen ◽  
Hesham Sheikh ◽  
Jonathan R Wolpaw
Keyword(s):  
Motor Units ◽  
Triceps Surae ◽  
Nerve Cuff ◽  
Intramuscular Electrodes

Hoffmann reflex is increased after 14 days of daily repeated Achilles tendon vibration for the soleus but not for the gastrocnemii muscles

2012 ◽  
Vol 37 (1) ◽  
pp. 14-20 ◽  
Author(s):  
Thomas Lapole ◽  
Chantal Pérot
Keyword(s):  
Achilles Tendon ◽  
Motor Units ◽  
Muscle Spindles ◽  
Triceps Surae ◽  
Control Group ◽  
Tendon Vibration ◽  
Hoffmann Reflex ◽  
Reflex Excitability ◽  
Short Period ◽  
Post Test

In a previous study, Achilles tendon vibrations were enough to improve the triceps surae (TS) activation capacities and also to slightly increase TS Hoffmann reflex (H-reflex) obtained by summing up soleus (Sol) and gastrocnemii (GM and GL) EMGs. The purpose of the present study was to analyze separately Sol and GM or GL reflexes to account for different effects of the vibrations on the reflex excitability of the slow soleus and of the gastrocnemii muscles. A control group (n = 13) and a vibration group (n = 16) were tested in pre-test and post-test conditions. The Achilles tendon vibration program consisted of 1 h of daily vibration (frequency: 50 Hz) applied during 14 days. Maximal Sol, GM and GL H-reflexes, and M-waves were recorded, and their Hmax/Mmax ratios gave the index of reflex excitability. After the vibration protocol, only Sol Hmax/Mmax was enhanced (p < 0.001). The enhanced Sol reflex excitability after vibration is in favor of a decrease in the pre-synaptic inhibition due to the repeated vibrations and the high solicitation of the reflex pathway. Those results of a short period of vibration applied at rest may be limited to the soleus because of its high density in muscle spindles and slow motor units, both structures being very sensitive to vibrations.

Declining inhibition in ipsi- and contralateral lumbar motoneurons during contractions of an ankle extensor muscle in the cat

1993 ◽  
Vol 70 (5) ◽  
pp. 1797-1804 ◽  
Author(s):  
J. Lafleur ◽  
D. Zytnicki ◽  
G. Horcholle-Bossavit ◽  
L. Jami
Keyword(s):  
Experimental Approach ◽  
Motor Units ◽  
Companion Paper ◽  
Triceps Surae ◽  
Rapid Decline ◽  
Knee Flexor ◽  
Extensor Muscles ◽  
Level 3 ◽  
Tendon Organs ◽  
Group Ii Afferents

1. Motoneurons of pretibial ankle flexor and knee flexor and extensor muscles were recorded intracellularly in chloralose- or pentobarbitone-anesthetized cats during sustained submaximal contractions of either ipsi- or contralateral gastrocnemius medialis muscle (GM). 2. In a majority of ipsilateral motoneurons, a sustained GM contraction elicited inhibitory potentials that quickly subsided before the end of the contraction. An abrupt increase in contractile force could elicit a new series of inhibitory potentials, which declined again in spite of a maintained force level. 3. Contraction-induced effects were only exceptionally detected in contralateral triceps surae and plantaris motoneurons. In a small number of pretibial flexor and knee flexor and extensor motoneurons, declining inhibitions were observed during sustained contractions of the contralateral GM muscle. 4. At the onset of GM contractions, a variety of motoneurons uniformly receive inhibitory inputs that are quickly filtered out. Although the functional significance of this widespread initial inhibition remains to be elucidated, its rapid decline seems useful to allow subsequent recruitment of motor units as may be required for coordination of posture and movement. 5. Tendon organs are activated during muscle contraction, but it is not certain whether Ib inputs from GM can account for all the effects observed. Contribution of other afferents was considered and tested using a different experimental approach. The companion paper reports observations suggesting that effects elicited by group II afferents may cooperate in the contraction-induced inhibition of motoneurons.

scholarly journals Muscles from the same muscle group do not necessarily share common drive: evidence from the human triceps surae

2020 ◽  
Author(s):  
François Hug ◽  
Alessandro Del Vecchio ◽  
Simon Avrillon ◽  
Dario Farina ◽  
Kylie J. Tucker
Keyword(s):  
Motor Units ◽  
Muscle Group ◽  
Triceps Surae ◽  
Neural Drive ◽  
Flexible Control ◽  
Neural Origin ◽  
Density Surface ◽  
Motor Unit Action ◽  
Common Drive ◽  
Human Participants

It has been proposed that movements are produced through groups of muscles, or motor modules, activated by common neural commands. However, the neural origin of motor modules is still debated. Here, we used complementary approaches to determine: i) whether three muscles of the same muscle group (soleus, gastrocnemius medialis [GM] and lateralis [GL]) are activated by a common neural drive ; and ii) whether the neural drive to GM and GL could be differentially modified by altering the mechanical requirements of the task. Eighteen human participants performed an isometric standing heel raise and submaximal isometric plantarflexions (10%, 30%, 50% of maximal effort). High-density surface electromyography recordings were decomposed into motor unit action potentials and coherence analysis was applied on the motor units spike trains. We identified strong common drive to each muscle, but minimal common drive between the muscles. Further, large between-muscle differences were observed during the isometric plantarflexions, such as a delayed recruitment time of GL compared to GM and soleus motor units and opposite time-dependent changes in the estimates of neural drive to muscles during the torque plateau. Finally, the feet position adopted during the heel raise task (neutral vs internally rotated) affected only the GL neural drive with no change for GM. These results provide conclusive that not all anatomically defined synergist muscles are controlled by strong common neural drive. Independent drive to some muscles from the same muscle group may allow for more flexible control to comply with secondary goals such as joint stabilization.

Change in recruitment order of motor units in human parasternal intercostal muscles with sleep state

1993 ◽  
Vol 74 (6) ◽  
pp. 2718-2723 ◽  
Author(s):  
W. A. Whitelaw ◽  
K. P. Rimmer ◽  
H. S. Sun
Keyword(s):  
Sleep Stage ◽  
Human Subjects ◽  
Motor Units ◽  
Excitatory Input ◽  
Sleep State ◽  
Intercostal Muscles ◽  
Intramuscular Electrodes ◽  
Normal Human ◽  
Low Threshold ◽  
Recruitment Order

Recruitment order of individual motor units in the early part of inspiration in parasternal intercostal muscles was observed in normal human subjects during wakefulness and non-rapid-eye-movement sleep. Electromyograms from bipolar fine wire intramuscular electrodes were recorded while the subjects lay supine in a sleep laboratory, and sleep stage was determined by polysomnography. From wakefulness to sleep there were numerous examples of shifts in order of recruitment among the low threshold units of early inspiration. There were corresponding shifts in the order of derecruitment of these units. Analysis of frequency of firing of units also suggested that the levels of excitatory input to one unit of a pair could be altered relative to the level of input of the other one. The data imply that there are at least minor differences in distribution of excitatory inputs from various sources among motoneurons of this muscle pool.

scholarly journals Effect of reflexive activation of motor units on torque development during electrically-evoked contractions of the triceps surae muscle

2019 ◽  
Vol 126 (2) ◽  
pp. 386-392 ◽  
Author(s):  
Florian Vitry ◽  
Alain Martin ◽  
Gaëlle Deley ◽  
Maria Papaiordanidou
Keyword(s):  
Tibial Nerve ◽  
Motor Evoked Potential ◽  
Motor Units ◽  
Triceps Surae ◽  
Emg Activity ◽  
Main Role ◽  
Frequency Dependent ◽  
Before And After ◽  
Spinal Excitability ◽  
Torque Development

The aim of the study was to identify stimulation conditions permitting the occurrence of extra torque (ET) and to examine their impact on spinal and corticospinal excitabilities. Twelve subjects received stimulation trains over the tibial nerve (20 s duration, 1 ms pulse duration) that were delivered at 3 stimulation frequencies (20, 50, and 100 Hz) and at 5 intensities (110%, 120%, 130%, 140%, and 150% of the motor threshold). Torque-time integral (TTI) of each stimulation train was calculated. Spinal [maximum H-reflex (Hmax)/maximal M-wave (Mmax)] and corticospinal [maximal motor evoked potential amplitude (MEPmax)/Mmax] excitabilities were assessed at rest before and after each stimulation train by tibial nerve stimulation and by transcranial magnetic stimulation, respectively. Moreover, a twitch at each stimulation intensity was delivered before and after each stimulation train. The EMG activity associated with this twitch was analyzed to identify the initial motor unit (MU) recruitment pathway before each stimulation train and discriminate trials to H-trials (indirect recruitment) and M-trials (direct recruitment). TTI was higher for H-trials compared with M-trials for all tested frequencies. There was a decrease in Hmax/Mmax for the 20 Hz-H trials and an increase for the 100 Hz-H trials, whereas MEPmax/Mmax remained unchanged at post measurements. Present results demonstrate that the initial MU recruitment pattern plays a main role in the ET occurrence, with the indirect recruitment via the afferent volley being substantial for its development. The modulations of Hmax/Mmax without changes in MEPmax/Mmax suggest that the ET development affects spinal excitability and that these changes are frequency dependent. NEW & NOTEWORTHY This study brings new insights into the stimulation conditions permitting the development of extra torque. An initial indirect recruitment of motor units, inducing reflex activation of spinal neurons through Ia afferent solicitation, appears a prerequisite for extra torque development. Under these conditions, spinal excitability modulations were frequency dependent.

Sag During Unfused Tetanic Contractions in Rat Triceps Surae Motor Units

1999 ◽  
Vol 81 (6) ◽  
pp. 2647-2661 ◽  
Author(s):  
J. S. Carp ◽  
P. A. Herchenroder ◽  
X. Y. Chen ◽  
J. R. Wolpaw
Keyword(s):  
Relaxation Times ◽  
Motor Units ◽  
Contractile Properties ◽  
Triceps Surae ◽  
Initial Increase ◽  
Tetanic Stimulation ◽  
Twitch Contraction ◽  
Time To Peak ◽  
Single Motor Units ◽  
Initial Force

Sag during unfused tetanic contractions in rat triceps surae motor units. Contractile properties and conduction velocity were studied in 202 single motor units of intact rat triceps surae muscles activated by intra-axonal (or intra-myelin) current injection in L5 or L6 ventral root to assess the factors that determine the expression of sag (i.e., decline in force after initial increase during unfused tetanic stimulation). Sag was consistently detected in motor units with unpotentiated twitch contraction times <20 ms. However, the range of frequencies at which sag was expressed varied among motor units such that there was no single interstimulus interval (ISI), with or without adjusting for twitch contraction time, at which sag could be detected reliably. Further analysis indicated that using the absence of sag as a criterion for identifying slow-twitch motor units requires testing with tetani at several different ISIs. In motor units with sag, the shape of the force profile varied with tetanic frequency and contractile properties. Simple sag force profiles (single maximum reached late in the tetanus followed by monotonic decay) tended to occur at shorter ISIs and were observed more frequently in fatigue-resistant motor units with long half-relaxation times and small twitch amplitudes. Complex sag profiles reached an initial maximum early in the tetanus, tended to occur at longer ISIs, and were more common in fatigue-sensitive motor units with long half-relaxation times and large twitch amplitudes. The differences in frequency dependence and force maximum location suggested that these phenomena represented discrete entities. Successive stimuli elicited near-linear increments in force during tetani in motor units that never exhibited sag. In motor units with at least one tetanus displaying sag, tetanic stimulation elicited large initial force increments followed by rapidly decreasing force increments. That the latter force envelope pattern occurred in these units even in tetani without sag suggested that the factors responsible for sag were expressed in the absence of overt sag. The time-to-peak force (TTP) of the individual contractions during a tetanus decreased in tetani with sag. Differences in the pattern of TTP change during a tetanus were consistent with the differences in force maximum location between tetani exhibiting simple and complex sag. Tetani from motor units that never exhibited sag did not display a net decrease in TTP during successive contractions. These data were consistent with the initial force decrement of sag resulting from a transient reduction in the duration of the contractile state.

Possible mechanisms of muscle cramp from temporal and spatial surface EMG characteristics

2000 ◽  
Vol 88 (5) ◽  
pp. 1698-1706 ◽  
Author(s):  
K. Roeleveld ◽  
B. G. M. van Engelen ◽  
D. F. Stegeman
Keyword(s):  
Maximal Voluntary Contraction ◽  
Muscle Fibers ◽  
Motor Units ◽  
Spatial Arrangement ◽  
Surface Emg ◽  
Voluntary Contraction ◽  
Triceps Surae ◽  
Muscle Cramp ◽  
Channel Surface ◽  
Temporal And Spatial

In this study, the initiation and development of muscle cramp are investigated. For this, we used a 64-channel surface electromyogram (EMG) to study the triceps surae muscle during both cramp and maximal voluntary contraction (MVC) in four cramp-prone subjects and during cramp only in another four cramp-prone subjects. The results show that cramp presents itself as a contraction of a slowly moving fraction of muscle fibers, indicating that either the spatial arrangement of the motoneurons and muscle fibers is highly related or that cramp spreads at a level close to the muscle. Spectral analyses of the EMG and peak-triggered average potentials show the presence of extremely short potentials during cramp compared with during MVC. These results can also be interpreted in two ways. Either the motoneurons fire with enlarged synchronization during MVC compared with cramp, or smaller units than motor units are active, indicating that cramp is initiated close to or even at the muscle fiber level. Further research is needed to draw final conclusions.

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