The Length of Tibialis Anterior Does Not Influence Force Steadiness During Submaximal Isometric Contractions with the Dorsiflexors

2021 ◽  
pp. 1-23
Author(s):  
Eirini Tsatsaki ◽  
Ioannis G Amiridis ◽  
Ales Holobar ◽  
Georgios Trypidakis ◽  
Fotini Arabatzi ◽  
...  
Keyword(s):  
Tibialis Anterior ◽  
Isometric Contractions ◽  
Force Steadiness

Positive Proprioceptive Feedback Elicited By Isometric Contractions of Ankle Flexors on Pretibial Motoneurons in Cats

2002 ◽  
Vol 88 (5) ◽  
pp. 2207-2214 ◽  
Author(s):  
L. Brizzi ◽  
L. H. Ting ◽  
D. Zytnicki
Keyword(s):  
Electrical Stimulation ◽  
Positive Feedback ◽  
Tibialis Anterior ◽  
Extensor Digitorum Longus ◽  
Motor Units ◽  
Extensor Digitorum ◽  
Isometric Contractions ◽  
Postsynaptic Potentials ◽  
Group I ◽  
Stimulation Of

Pretibial flexor motoneurons were recorded intracellularly in anesthetized cats during unfused isometric contractions of a subpopulation of motor units from either tibialis anterior (TA) or extensor digitorum longus (EDL) muscles. The contractions elicited excitatory postsynaptic potentials in 23 of 28 pretibial flexor motoneurons. No effect was observed in the remaining motoneurons. In control experiments, the effects of electrical stimulation of afferents within the TA nerve were investigated to help identify afferents responsible for the contraction-induced positive feedback. This feedback was ascribed to actions of Ia fibers because the pattern of the contraction-induced excitatory potentials was consistent with the known pattern of Ia discharge; in control experiments, electrical stimulation of group I fibers elicited only monosynaptic excitatory potentials; and the distribution of both the contraction-induced positive feedback among motor nuclei as well as the electrically evoked Ia excitatory monosynaptic potentials were restricted to homonymous and synergic motoneurons. Observation of the Ia contraction-induced positive feedback was facilitated by the absence of Ib autogenic inhibition. This contraction-induced Ia excitatory feedback in ankle flexors might either reinforce Ia-induced reflexes when these muscles are lengthened or help to lift the leg over an obstacle.

scholarly journals Nonlinear summation of force in cat tibialis anterior: a muscle with intrafascicularly terminating fibers

2003 ◽  
Vol 94 (5) ◽  
pp. 1955-1963 ◽  
Author(s):  
Thomas G. Sandercock
Keyword(s):  
Tibialis Anterior ◽  
Muscle Length ◽  
Tissue Structure ◽  
Isometric Contractions ◽  
Linear Summation ◽  
In Series ◽  
The Common ◽  
Ventral Roots ◽  
Whole Muscle ◽  
Connective Tissue Structure

The complex connective tissue structure of muscle and tendon suggests that forces from two parts of a muscle may not summate linearly, particularly in muscles with intrafasciculary terminating fibers, such as cat tibialis anterior (TA). In four anesthetized cats, the TA was attached to a servomechanism to control muscle length and record force. The ventral roots were divided into two bundles, each innervating about half the TA, so the two parts could be stimulated alone or together. Nonlinear summation of force ( F nl) was measured during isometric contractions. F nl was small and negative, indicating less than linear summation of the parts, which is consistent with the predicted F nl of muscle fibers connected in series. F nl was more significant when smaller parts of the muscle were tested (21.8 vs. 8% for whole muscle). These data were fit to a model where both parts of the muscle were assumed to stretch a common elasticity. Compensatory movements of the servomechanism showed the common elasticity is very stiff, and the model cannot account for F nl in cat TA.

scholarly journals Discharge properties of motor units during steady isometric contractions performed with the dorsiflexor muscles

2012 ◽  
Vol 112 (11) ◽  
pp. 1897-1905 ◽  
Author(s):  
Mark Jesunathadas ◽  
Malgorzata Klass ◽  
Jacques Duchateau ◽  
Roger M. Enoka
Keyword(s):  
Tibialis Anterior ◽  
Interspike Interval ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Isometric Contractions ◽  
Discharge Characteristics ◽  
Recruitment Threshold ◽  
Discharge Rates ◽  
Contraction Times ◽  
Experimental Values

The purpose of this study was to record the discharge characteristics of tibialis anterior motor units over a range of target forces and to import these data, along with previously reported observations, into a computational model to compare experimental and simulated measures of torque variability during isometric contractions with the dorsiflexor muscles. The discharge characteristics of 44 motor units were quantified during brief isometric contractions at torques that ranged from recruitment threshold to an average of 22 ± 14.4% maximal voluntary contraction (MVC) torque above recruitment threshold. The minimal [range: 5.8–19.8 pulses per second (pps)] and peak (range: 8.6–37.5 pps) discharge rates of motor units were positively related to the recruitment threshold torque ( R2 ≥ 0.266; P < 0.001). The coefficient of variation for interspike interval at recruitment was positively associated with recruitment threshold torque ( R2 = 0.443; P < 0.001) and either decreased exponentially or remained constant as target torque increased above recruitment threshold torque. The variability in the simulated torque did not differ from the experimental values once the recruitment range was set to ∼85% MVC torque, and the association between motor twitch contraction times and peak twitch torque was defined as a weak linear association ( R2 = 0.096; P < 0.001). These results indicate that the steadiness of isometric contractions performed with the dorsiflexor muscle depended more on the distributions of mechanical properties than discharge properties across the population of motor units in the tibialis anterior.

Force Steadiness: From Motor Units to Voluntary Actions

Physiology ◽  
2021 ◽  
Vol 36 (2) ◽  
pp. 114-130 ◽  
Author(s):  
Roger M. Enoka ◽  
Dario Farina
Keyword(s):  
Motor Function ◽  
Motor Neurons ◽  
Motor Units ◽  
Isometric Contractions ◽  
Strongly Correlated ◽  
Synaptic Inputs ◽  
Force Steadiness ◽  
Spinal Motor Neurons ◽  
Spinal Motor

Voluntary actions are controlled by the synaptic inputs that are shared by pools of spinal motor neurons. The slow common oscillations in the discharge times of motor units due to these synaptic inputs are strongly correlated with the fluctuations in force during submaximal isometric contractions (force steadiness) and moderately associated with performance scores on some tests of motor function. However, there are key gaps in knowledge that limit the interpretation of differences in force steadiness.

Physiological tremor is suppressed and force steadiness is enhanced with increased availability of serotonin regardless of muscle fatigue

2021 ◽  
Author(s):  
Tyler Thomas Henderson ◽  
Jacob R Thorstensen ◽  
Steven Morrison ◽  
Murray G Tucker ◽  
Justin J Kavanagh
Keyword(s):  
Steady State ◽  
Peak Power ◽  
Elbow Flexion ◽  
Voluntary Contraction ◽  
Isometric Contractions ◽  
Physiological Tremor ◽  
Constant Force ◽  
Force Steadiness ◽  
Main Effects ◽  
Flexion Force

Although there is evidence that 5-HT acts as an excitatory neuromodulator to enhance maximal force generation, it is largely unknown how 5-HT activity influences the ability to sustain a constant force during steady-state contractions. A total of 22 healthy individuals participated in the study, where elbow flexion force was assessed during brief isometric contractions at 10% maximal voluntary contraction (MVC), 60% MVC, MVC, and during a sustained MVC. The selective serotonin reuptake inhibitor, paroxetine, suppressed physiological tremor and increased force steadiness when performing the isometric contractions. In particular, a main effect of drug was detected for peak power of force within the 8-12 Hz range (p = 0.004) and the coefficient of variation (CV) of force (p < 0.001). A second experiment was performed where intermittent isometric elbow flexions (20% MVC sustained for 2 min) were repeatedly performed so that serotonergic effects on physiological tremor and force steadiness could be assessed during the development of fatigue. Main effects of drug were once again detected for peak power of force in the 8-12 Hz range (p = 0.002) and CV of force (p = 0.003), where paroxetine suppressed physiological tremor and increased force steadiness when the elbow flexors were fatigued. The findings of this study suggest that enhanced availability of 5-HT in humans has a profound influence of maintaining constant force during steady state contractions. The action of 5-HT appears to suppress fluctuations in force regardless of the fatigue state of the muscle.

Fine structure of early degenerating myofibers in the tibialis anterior of young ‘MDX’ mouse

1988 ◽  
Vol 46 ◽  
pp. 322-323
Author(s):  
H.D. Geissinger ◽  
C.K. McDonald-Taylor
Keyword(s):  
Fine Structure ◽  
Muscle Regeneration ◽  
Tibialis Anterior ◽  
Genetic Defect ◽  
Mdx Mouse ◽  
Mdx Mice ◽  
Histopathological Changes ◽  
Electron Microscopic ◽  
Dystrophic Mouse ◽  
Preliminary Study

A new strain of mice, which had arisen by mutation from a dystrophic mouse colony was designated ‘mdx’, because the genetic defect, which manifests itself in brief periods of muscle destruction followed by episodes of muscle regeneration appears to be X-linked. Further studies of histopathological changes in muscle from ‘mdx’ mice at the light microscopic or electron microscopic levels have been published, but only one preliminary study has been on the tibialis anterior (TA) of ‘mdx’ mice less than four weeks old. Lesions in the ‘mdx’ mice vary between different muscles, and centronucleation of fibers in all muscles studied so far appears to be especially prominent in older mice. Lesions in young ‘mdx’ mice have not been studied extensively, and the results appear to be at variance with one another. The degenerative and regenerative aspects of the lesions in the TA of 23 to 26-day-old ‘mdx’ mice appear to vary quantitatively.

Regenerating myofibers in tibialis anterior muscles of young ‘MDX’ mice

1987 ◽  
Vol 45 ◽  
pp. 726-727
Author(s):  
H. D. Geissinge ◽  
L.D. Rhodes
Keyword(s):  
Muscular Dystrophy ◽  
Mouse Model ◽  
Tibialis Anterior ◽  
Physiological Activity ◽  
Mdx Mice ◽  
Mode Of Inheritance

A recently discovered mouse model (‘mdx’) for muscular dystrophy in man may be of considerable interest, since the disease in ‘mdx’ mice is inherited by the same mode of inheritance (X-linked) as the human Duchenne (DMD) muscular dystrophy. Unlike DMD, which results in a situation in which the continual muscle destruction cannot keep up with abortive regenerative attempts of the musculature, and the sufferers of the disease die early, the disease in ‘mdx’ mice appears to be transient, and the mice do not die as a result of it. In fact, it has been reported that the severely damaged Tibialis anterior (TA) muscles of ‘mdx’ mice seem to display exceptionally good regenerative powers at 4-6 weeks, so much so, that these muscles are able to regenerate spontaneously up to their previous levels of physiological activity.

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