Influence of fatigue and velocity on the latency and recruitment order of scapular muscles

1. The effects of four different synaptic input systems on the recruitment order within a mammalian motoneuron pool were investigated using computer simulations. The synaptic inputs and motor unit properties in the model were based as closely as possible on the available experimental data for the cat medial gastrocnemius pool and muscle. Monte Carlo techniques were employed to add random variance to the motor unit thresholds and forces and to sample the resulting recruitment orders. 2. The effects of the synaptic inputs on recruitment order depended on how they modified the range of recruitment thresholds established by differences in the intrinsic current thresholds of the motoneurons. Application of a uniform synaptic input to the pool (i.e., distributed equally to all motoneurons) resulted in a recruitment sequence that was quite stable even with the addition of large amounts of random variance. With 50% added random variance, the recruitment reversals did not exceed 8%. 3. The simulated monosynaptic input from homonymous Ia afferent fibers generated a twofold expansion of the range of recruitment thresholds beyond that attributed to the differences in the intrinsic current thresholds. The Ia input generated a small reduction in the number of recruitment reversals due to random variance (6% reversals at 50% random variance). The simulated monosynaptic vestibulospinal input generated a twofold compression of the range of recruitment thresholds that exerted a modest increase in the number of recruitment reversals (12% reversals at 50% random variance). 4. In comparison with the modest effects of the two monosynaptic inputs, the simulated oligosynpatic rubrospinal excitatory input exerted a nine-fold compression in the recruitment threshold range that resulted in a recruitment sequence that was highly sensitive to random variance. With 50% added random variance, the sequence became nearly random (40% reversals). 5. Reciprocal Ia inhibition was simulated by a uniform distribution within the pool, but its effects on recruitment order were highly dependent on the distribution of the excitatory input. Reciprocal inhibition exerted only minor effects on recruitment order when combined with the Ia or vestibulospinal inputs. However, when the excitatory drive was supplied by the rubrospinal input, even small amounts of reciprocal inhibition were sufficient to completely reverse the normal recruitment sequence. 6. The simulated monosynaptic Ia input was highly effective in compensating for the disruptive effects of rubrospinal excitation on recruitment order. Even a small Ia bias combined with the rubrospinal excitation was sufficient to halve the effects of random variance and to restore the normal recruitment sequence in the presence of rather large amounts of reciprocal inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

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The recruitment order of scapular muscles depends on the characteristics of the postural task

Journal of Electromyography and Kinesiology ◽

10.1016/j.jelekin.2016.09.001 ◽

2016 ◽

Vol 31 ◽

pp. 40-47 ◽

Cited By ~ 6

Author(s):

Guillermo Mendez-Rebolledo ◽

Valeska Gatica-Rojas ◽

Eduardo Martinez-Valdes ◽

H.B. Xie

Keyword(s):

Recruitment Order ◽

Postural Task

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Twitch Tension, Spike Amplitude and Recruitment Order of Masseter Muscle Single Motor Units

Oral Physiology and Occlusion ◽

10.1016/b978-0-08-023183-9.50013-2 ◽

1978 ◽

pp. 78-90 ◽

Cited By ~ 1

Author(s):

Louis J. Goldberg

Keyword(s):

Masseter Muscle ◽

Motor Units ◽

Single Motor ◽

Spike Amplitude ◽

Single Motor Units ◽

Recruitment Order

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Recruitment Order Among Motoneurons From Different Motor Nuclei

Journal of Neurophysiology ◽

10.1152/jn.1999.81.5.2485 ◽

1999 ◽

Vol 81 (5) ◽

pp. 2485-2492 ◽

Cited By ~ 14

Author(s):

Alan J. Sokoloff ◽

Sondra G. Siegel ◽

Timothy C. Cope

Keyword(s):

Conduction Velocity ◽

Biceps Femoris ◽

Medial Gastrocnemius ◽

Size Principle ◽

Lateral Gastrocnemius ◽

Decerebrate Cat ◽

Ankle Muscles ◽

Recruitment Order ◽

Motor Nuclei ◽

First Time

Recruitment order among motoneurons from different motor nuclei. The principles by which motoneurons (MNs) innervating different multiple muscles are organized into activity are not known. Here we test the hypothesis that coactivated MNs belonging to different muscles in the decerebrate cat are recruited in accordance with the size principle, i.e., that MNs with slow conduction velocity (CV) are recruited before MNs with higher CV. We studied MN recruitment in two muscle pairs, the lateral gastrocnemius (LG) and medial gastrocnemius (MG) muscles, and the MG and posterior biceps femoris (PBF) muscles because these pairs are coactivated reliably in stretch and cutaneous reflexes, respectively. For 29/34 MG-LG pairs of MNs, the MN with lower CV was recruited first either in all trials (548/548 trials for 22 pairs) or in most trials (225/246 trials for 7 pairs), whether the MG or the LG MN in a pair was recruited first. Intertrial variability in the force thresholds of MG and LG MNs recruited by stretch was relatively low (coefficient of variation = 18% on average). Finally, punctate stimulation of the skin over the heel recruited 4/4 pairs of MG-LG MNs in order by CV. By all of these measures, recruitment order is as consistent among MNs from these two ankle muscles as it is for MNs supplying the MG muscle alone. For MG-PBF pairings, the MN with lower CV was recruited first in the majority of trials for 13/24 pairs and in reverse order for 9/24 pairs. The recruitment sequence of coactive MNs supplying the MG and PBF muscles was, therefore, random with respect to axonal conduction velocity and not organized as predicted by the size principle. Taken together, these findings demonstrate for the first time, that the size principle can extend beyond the boundaries of a single muscle but does not coordinate all coactive muscles in a limb.

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Recruitment order of motoneurons during functional tasks

Experimental Brain Research ◽

10.1007/bf00229189 ◽

1994 ◽

Vol 79 (2) ◽

Author(s):

K.E. Jones ◽

M. Lyons ◽

P. Bawa ◽

R.N. Lemon

Keyword(s):

Recruitment Order

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Recruitment Order of Cat Abducens Motoneurons and Internuclear Neurons

Journal of Neurophysiology ◽

10.1152/jn.00402.2003 ◽

2003 ◽

Vol 90 (4) ◽

pp. 2240-2252 ◽

Cited By ~ 14

Author(s):

Ángel M. Pastor ◽

David González-Forero

Keyword(s):

Rectus Muscle ◽

Neuronal Firing ◽

Eye Position ◽

High Dose ◽

Recruitment Threshold ◽

Ocular Reflex ◽

Lateral Rectus Muscle ◽

Vestibulo Ocular Reflex ◽

Recruitment Order ◽

Eye Velocity

Abducens neurons undergo a dose-dependent synaptic blockade (either disinhibition or complete blockade) when tetanus neurotoxin (TeNT) is injected into the lateral rectus muscle at either a low (0.5) or a high dose (5 ng/kg). We studied the firing pattern and recruitment order in abducens neurons both in control and after TeNT injection. The eye position threshold for recruitment of control abducens neurons was exponentially related to the eye position and velocity sensitivities. We also found a constancy of recruitment threshold for different eye movement modalities (spontaneous, optokinetic, and vestibular). Exponential relationships were found, as well, for eye velocity sensitivity during saccades and for position and velocity sensitivities during the vestibulo-ocular reflex. Likewise, inverse relationships were found between recruitment threshold or position sensitivity with the antidromic latency in control abducens neurons. These relationships, however, did not apply following TeNT treatment. Neuronal firing after TeNT appeared either disinhibited (low dose) or depressed (high dose), but the relationships between neuronal sensitivities and recruitment still applied. However, the pattern of recruitment shifted toward the treated side as more inputs were blocked by the low- and high-dose treatments, respectively. Nonetheless, although the recruitment-to-sensitivity relationships persisted under the TeNT synaptic blockade, we conclude that synaptic inputs are determinant for establishing the recruitment threshold and recruitment spacing of abducens motoneurons and internuclear neurons.

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Motor unit anatomy and physiology

10.1093/med/9780198754596.003.0006 ◽

2017 ◽

Author(s):

Matthew Pitt

Keyword(s):

Quantitative Analysis ◽

Motor Unit ◽

Interference Pattern ◽

Theoretical Explanation ◽

Motor Unit Potential ◽

Amplitude Analysis ◽

Anatomy And Physiology ◽

Needle Electromyography ◽

Accurate Quantitative Analysis ◽

Recruitment Order

This chapter focuses on the signals recorded with needle electromyography (EMG) and the measurement of their specific parameters. These parameters include duration, amplitude, number of phases, and stability. The concept of the electrophysiologic biopsy and the explanation of unusual findings seen on EMG are introduced. In relation to the interference pattern, discussions of the firing rate, recruitment order, and interference pattern are given. Moving from the theoretical explanation of the findings, the problems of the accurate quantitative analysis of the motor unit potential are discussed and measures to improve quantification, particularly in children, are highlighted. The importance of filter settings, the storage of signals, and the different ways of collecting and analysing the potentials are all covered. This section finishes with discussion of the normative range for motor unit duration, and concludes with the automatic analysis of the interference pattern, including turns/amplitude analysis, number of short segments measurement, and envelope analysis.

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Motor-unit recruitment in the decerebrate cat: several unit properties are equally good predictors of order

Journal of Neurophysiology ◽

10.1152/jn.1991.66.4.1127 ◽

1991 ◽

Vol 66 (4) ◽

pp. 1127-1138 ◽

Cited By ~ 41

Author(s):

T. C. Cope ◽

B. D. Clark

Keyword(s):

Motor Unit ◽

Rank Order ◽

Motor Units ◽

Afferent Input ◽

Medial Gastrocnemius ◽

Size Principle ◽

Recruitment Pattern ◽

Decerebrate Cat ◽

Recruitment Order ◽

Stimulation Of

1. Recruitment order was studied in pairs of motor units of the medial gastrocnemius (MG) muscle of decerebrate cats with the use of dual microelectrode recording from intact ventral root filaments. Excitation was provided by stretch of MG, stretch of synergists [lateral gastrocnemius (LG), plantaris (PL), and soleus (SOL) muscles] or electrical stimulation of the caudal cutaneous sural (CCS) nerve. Motor units were characterized by axonal conduction velocity (CV), tetanic tension (Pmax), twitch contraction time (CT), and fatigue index (FI). 2. Consistent with the recruitment pattern described by others, most often in relation to either CV or Pmax, the first unit of a pair to be recruited by MG stretch was typically the one with the lower CV and Pmax, and the higher FI and CT. The proportion of pairs that agreed in rank order of each property and recruitment order was as follows: for CT, 94%; for CV, 87%; for Pmax, 84%; and for FI, 75%. With a single marginal exception (CT vs. FI), no motor-unit property proved to be significantly better than the others at predicting recruitment (G test; P greater than 0.05). 3. In all 11 tested pairs containing one slow (type S) and one fast (type F) unit, the S was more easily recruited by stretch. Type F units divided into groups with high (type FR), low (type FF), and intermediate (type FInt) values for FI were recruited in order from FR to FInt to FF in 8/11 pairs. Thus our findings were similar to earlier demonstrations that recruitment proceeds in order by type. 4. Stretch of MG synergists usually recruited units in the same order as MG stretch. In two S-S pairs, recruitment order was switched with synergist stretch. 5. Stimulation of the CCS nerve was generally excitatory to the MG units sampled. Most unit pairs were recruited by CCS stimulation in the same order as by MG stretch, but, for 6 of 39 pairs, CCS stimulation switched the order produced by stretch. Thus, whereas sural afferent input can preferentially excite some units over others as suggested by Kanda et al., that effect is not widespread or selective for unit type under these conditions. 6. Assuming that all MG motor units cooperate as a single functional pool in homonymous stretch reflexes, we support others in concluding that a motoneuron's recruitment threshold is not strictly determined by its size. However, our data do not distinguish other schemes that predict recruitment order more accurately than the size principle.(ABSTRACT TRUNCATED AT 400 WORDS)

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Cutaneous stimulation fails to alter motor unit recruitment in the decerebrate cat

Journal of Neurophysiology ◽

10.1152/jn.1993.70.4.1433 ◽

1993 ◽

Vol 70 (4) ◽

pp. 1433-1439 ◽

Cited By ~ 30

Author(s):

B. D. Clark ◽

S. M. Dacko ◽

T. C. Cope

Keyword(s):

Motor Unit ◽

Conduction Velocity ◽

Motor Units ◽

Firing Frequency ◽

Medial Gastrocnemius ◽

Electromyographic Activity ◽

Size Principle ◽

Decerebrate Cat ◽

Slow Twitch ◽

Recruitment Order

1. An attempt was made to repeat the observation that cutaneous input to the cat medial gastrocnemius (MG) muscle sometimes had the differential effect of inhibiting motoneurons with slow axonal conduction velocity while simultaneously exciting others with fast conduction velocity. Dual microelectrode recording from intact ventral root filaments was used to study the effects of cutaneous inputs on recruitment order and on firing frequency of physiologically characterized MG motor units in decerebrate cats. Motor responses to pinch of the skin over the lateral surface of the ankle as well as electrical stimulation of the caudal cutaneous sural (CCS) nerve were contrasted with the responses to static muscle stretch as well as muscle vibration. 2. In contrast to the prediction, recruitment order in pairwise tests was the same for skin pinch or CCS stimulation as it was for MG stretch or vibration in all 32 tested pairs of motor units. This sample included seven pairs comprising one slow-twitch (S) and one fast-twitch motor unit, where the predicted reversal of recruitment should have been most apparent. Regardless of the source of excitation, recruitment of motor units of the MG was consistent with Henneman's size principle in approximately 90% of trials. 3. Skin pinch increased the firing rate of 30 of 32 individual motor units previously activated by stretch or vibration, including 7 slow-twitch units. In the remaining two units, skin pinch transiently (100-400 ms) slowed the firing of an S unit in 11 of 13 vibration + pinch trials. The other unit (type unknown) showed one or two retarded spikes in each of four vibration + pinch trials. In three S units, including the lone inhibitable unit and two others that were only excited by skin pinch, there was a significant positive rank correlation between change in unit firing frequency and change in soleus integrated electromyographic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

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