Mechanical Properties and Behaviour of Motor Units in the Tibialis Anterior During Voluntary Contractions

1997 ◽  
Vol 22 (6) ◽  
pp. 585-597 ◽  
Author(s):  
Michaël Van Cutsem ◽  
Patrick Feiereisen ◽  
Jacques Duchateau ◽  
Karl Hainaut
Keyword(s):  
Mechanical Properties ◽  
Tibialis Anterior ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Recruitment Threshold ◽  
Time To Peak ◽  
Spike Triggered Averaging ◽  
The Mean ◽  
Voluntary Contractions ◽  
Mean Time

The present work was carried out to analyse the properties and behaviour of Tibialis anterior motor units (MUs) during voluntary contractions in humans. A total of 528 single MU mechanical properties was recorded in 10 subjects by means of the spike-triggered averaging (STA) technique. MU recruitment thresholds and discharge frequencies were recorded during linearly increasing maximal voluntary contraction (MVC). The results indicate a mean (±SD) MU torque of 25.5 ± 21.5 mN•m. and a mean time-to-peak of 45.6 ± 13.6 ms. A comparison of the average MU twitch torque with that of the muscle allowed an estimate of about 300 MUs in the Tibialis anterior. A positive linear relationship was recorded between the MU twitch torque and the recruitment threshold. The mean minimal and maximal discharge frequencies of MUs were 8.4 ± 3.0 Hz and 33.2 ± 14.7 Hz, respectively. The results of the present work indicate that MU behaviour during voluntary contractions is different in the tibialis anterior and in the adductor pollicis. Key words: discharge frequency, recruitment threshold, motor unit count

Impulse propagation and muscle activation in long maximal voluntary contractions

1989 ◽  
Vol 67 (5) ◽  
pp. 1835-1842 ◽  
Author(s):  
C. K. Thomas ◽  
J. J. Woods ◽  
B. Bigland-Ritchie
Keyword(s):  
Tibialis Anterior ◽  
Muscle Activation ◽  
Motor Units ◽  
Voluntary Contraction ◽  
Mass Action ◽  
M Wave ◽  
Force Reduction ◽  
Small Decline ◽  
Voluntary Contractions ◽  
Do So

With fatigue, force generation may be limited by several factors, including impaired impulse transmission and/or reduced motor drive. In 5-min isometric maximal voluntary contraction, no decline was seen in the peak amplitude of the tibialis anterior compound muscle mass action potential (M wave) either during or immediately after the voluntary effort, provided maximal nerve stimulation was retained. For first dorsal interosseous (FDI) muscle, M wave amplitudes declined by 19.4 +/- 1.6% during the first 2 min but did not change significantly thereafter, despite the continued force reduction (up to 94% in 5 min for both muscles). The duration of the FDI M waves increased (greater than 30%), suggesting that the small decline in amplitude was the result of increased dispersion between the responses of different motor units. Some subjects kept FDI maximally activated throughout, but when they used tibialis anterior, twitch occlusion and tetanic muscle stimulation showed that most subjects were usually only able to do so for the first 60 s and thereafter only during brief “extra efforts.” Thus force loss during isometric voluntary contractions sustained at the highest intensities results mainly from failure of processes within the muscle fibers.

Absence of somatotopic projection of muscle afferents onto motoneurons of same muscle

1984 ◽  
Vol 51 (2) ◽  
pp. 185-194 ◽  
Author(s):  
B. McKeon ◽  
S. Gandevia ◽  
D. Burke
Keyword(s):  
Motor Unit ◽  
Tibialis Anterior ◽  
Motor Units ◽  
Muscle Afferents ◽  
Voluntary Contraction ◽  
Excitatory Postsynaptic Potential ◽  
Muscle Belly ◽  
Nerve Fascicle ◽  
Electrical Stimuli ◽  
Voluntary Contractions

During weak voluntary contractions, muscle afferents from a restricted region of the tibialis anterior of humans were activated with mechanical or electrical stimuli while electromyographic recordings (EMG) were made from pairs of motor units. One motor unit of a pair was located in the region of muscle from which the afferents arose; the other was at least 10 cm distal. The territories of the motor units of each pair did not overlap. All motor units were of low threshold, recruited at less than 5% of maximal voluntary strength. Direct recordings of muscle afferent activity, using a microelectrode in the nerve fascicle innervating the tibialis anterior, showed that taps delivered to the muscle belly activated submaximally a discrete population of receptors, restricted to the site of the taps. The spread of the disturbance set up by the taps or by vibration at 100 Hz applied to the muscle belly was measured with an accelerometer and was also found to be restricted to the site of application of the vibrator tip. With each of 12 pairs of motor units, vibration at 100 Hz was applied to the muscle near the motor unit of higher threshold for recruitment in a voluntary contraction. The vibration produced detectable reflex effects but did not alter recruitment order within any pair of motor units. During voluntary contractions involving 10 pairs of motor units, taps were applied to the muscle belly near each motor unit of a pair. The taps produced, at short latency, an increase in the probability of discharge of each motor unit. This change in probability is related to a composite excitatory postsynaptic potential (EPSP) caused by dynamically responding mechanoreceptors near the tap site and is generated through monosynaptic/oligosynaptic pathways. Taps near one motor unit of a pair did not selectively or preferentially affect the discharge of that motoneuron. During a voluntary contraction of tibialis anterior, electrical stimuli just below threshold for efferent axons, and so probably above threshold for afferent axons, were delivered singly and in brief trains through a microelectrode in a nerve fascicle innervating that muscle. Such stimulation had no detectable effect on the discharge pattern of four pairs of motor units. These findings suggest that the feedback from a few receptors in the muscle has a negligible effect on the motoneuron pool, in comparison with the total excitatory drive present during a voluntary contraction.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Pain-induced changes in motor unit discharge depend on recruitment threshold and contraction speed

2021 ◽  
Author(s):  
Eduardo Martinez-Valdes ◽  
Francesco Negro ◽  
Michail Arvanitidis ◽  
Dario Farina ◽  
Deborah Falla
Keyword(s):  
Discharge Rate ◽  
Tibialis Anterior Muscle ◽  
Maximum Voluntary Contraction ◽  
Motor Units ◽  
Inhibitory Effect ◽  
Voluntary Contraction ◽  
Recruitment Threshold ◽  
Contraction Speed ◽  
Discharge Rates ◽  
Hypertonic Saline Injection

At high forces, the discharge rates of lower and higher threshold motor units (MU) are influenced in a different way by muscle pain. These differential effects may be particularly important for performing contractions at different speeds since the proportion of lower and higher threshold MUs recruited varies with contraction velocity. We investigated whether MU discharge and recruitment strategies are differentially affected by pain depending on their recruitment threshold (RT), across a range of contraction speeds. Participants performed ankle dorsiflexion sinusoidal-isometric contractions at two frequencies (0.25Hz and 1Hz) and two modulation amplitudes [5% and 10% of the maximum voluntary contraction (MVC)] with a mean target torque of 20%MVC. High-density surface electromyography recordings from the tibialis anterior muscle were decomposed and the same MUs were tracked across painful (hypertonic saline injection) and non-painful conditions. Torque variability, mean discharge rate (MDR), DR variability (DRvar), RT and the delay between the cumulative spike train and the resultant torque output (neuromechanical delay, NMD) were assessed. The average RT was greater at faster contraction velocities (p=0.01) but was not affected by pain. At the fastest contraction speed, torque variability and DRvar were reduced (p<0.05) and MDR was maintained. Conversely, MDR decreased and DRvar and NMD increased significantly during pain at slow contraction speeds (p<0.05). These results show that reductions in contraction amplitude and increased recruitment of higher threshold MUs at fast contraction speeds appears to compensate for the inhibitory effect of nociceptive inputs on lower threshold MUs, allowing the exertion of fast submaximal contractions during pain.

Nonuniform strain of human soleus aponeurosis-tendon complex during submaximal voluntary contractions in vivo

2003 ◽  
Vol 95 (2) ◽  
pp. 829-837 ◽  
Author(s):  
Taija Finni ◽  
John A. Hodgson ◽  
Alex M. Lai ◽  
V. Reggie Edgerton ◽  
Shantanu Sinha
Keyword(s):  
Achilles Tendon ◽  
Maximal Voluntary Contraction ◽  
Three Dimensional ◽  
Motor Units ◽  
Magnetic Resonance Images ◽  
Voluntary Contraction ◽  
Force Transmission ◽  
Voluntary Contractions ◽  
Nonuniform Strain

The distribution of strain along the soleus aponeurosis tendon was examined during voluntary contractions in vivo. Eight subjects performed cyclic isometric contractions (20 and 40% of maximal voluntary contraction). Displacement and strain in the apparent Achilles tendon and in the aponeurosis were calculated from cine phase-contrast magnetic resonance images acquired with a field of view of 32 cm. The apparent Achilles tendon lengthened 2.8 and 4.7% in 20 and 40% maximal voluntary contraction, respectively. The midregion of the aponeurosis, below the gastrocnemius insertion, lengthened 1.2 and 2.2%, but the distal aponeurosis shortened 2.1 and 2.5%, respectively. There was considerable variation in the three-dimensional anatomy of the aponeurosis and muscle-tendon junction. We suggest that the nonuniformity in aponeurosis strain within an individual was due to the presence of active and passive motor units along the length of the muscle, causing variable force along the measurement site. Force transmission along intrasoleus connective tissue may also be a significant source of nonuniform strain in the aponeurosis.

Further evidence of incomplete neural control of muscle properties in cat tibialis anterior motor units

1995 ◽  
Vol 268 (2) ◽  
pp. C527-C534 ◽  
Author(s):  
G. A. Unguez ◽  
R. R. Roy ◽  
D. J. Pierotti ◽  
S. Bodine-Fowler ◽  
V. R. Edgerton
Keyword(s):  
Motor Unit ◽  
Tibialis Anterior ◽  
Neural Control ◽  
Periodic Acid ◽  
Muscle Fibers ◽  
Motor Units ◽  
Fiber Types ◽  
Muscle Properties ◽  
Periodic Acid Schiff ◽  
The Mean

To examine the influence of a motoneuron in maintaining the phenotype of the muscle fibers it innervates, myosin heavy chain (MHC) expression, succinate dehydrogenase (SDH) activity, and cross-sectional area (CSA) of a sample of fibers belonging to a motor unit were studied in the cat tibialis anterior 6 mo after the nerve branches innervating the anterior compartment were cut and sutured near the point of entry into the muscle. The mean, range, and coefficient of variation for the SDH activity and the CSA for both motor unit and non-motor unit fibers for each MHC profile and from each control and each self-reinnervated muscle studied was obtained. Eight motor units were isolated from self-reinnervated muscles using standard ventral root filament testing techniques, tested physiologically, and compared with four motor units from control muscles. Motor units from self-reinnervated muscles could be classified into the same physiological types as those found in control tibialis anterior muscles. The muscle fibers belonging to a unit were depleted of glycogen via repetitive stimulation and identified in periodic acid-Schiff-stained frozen sections. Whereas muscle fibers in control units expressed similar MHCs, each motor unit from self-reinnervated muscles contained a mixture of fiber types. In each motor unit, however, there was a predominance of fibers with the same MHC profile. The relative differences in the mean SDH activities found among fibers of different MHC profiles within a unit after self-reinnervation and those found among fibers in control muscles were similar, i.e., fast-2 < fast-1 < or = slow MHC fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Blood Flow Restriction Alters Motor Unit Behavior During Resistance Exercise

2019 ◽  
Vol 40 (09) ◽  
pp. 555-562 ◽  
Author(s):  
Pedro Fatela ◽  
Goncalo V. Mendonca ◽  
António Prieto Veloso ◽  
Janne Avela ◽  
Pedro Mil-Homens
Keyword(s):  
Blood Flow ◽  
Firing Rate ◽  
Motor Unit ◽  
Motor Units ◽  
Blood Flow Restriction ◽  
Motor Unit Recruitment ◽  
Recruitment Threshold ◽  
Firing Rates ◽  
Flow Restriction ◽  
Voluntary Contractions

AbstractWe aimed to determine whether blood flow restriction (BFR) alters the characteristics of individual motor units during low-intensity (LI) exercise. Eight men (26.0±3.8 yrs) performed 5 sets of 15 knee extensions at 20% of one-repetition maximum (with and without BFR). Maximal isometric voluntary contractions (MVC) were performed before and after exercise to quantify force decrement. Submaximal isometric voluntary contractions were additionally performed for 18 s, matching trapezoidal target-force trajectories at 40% pre-MVC. EMG activity was recorded from the vastus lateralis muscle. Then, signals were decomposed to extract motor unit recruitment threshold, firing rates and action potential amplitudes (MUAP). Force decrement was only seen after LI BFR exercise (–20.5%; p<0.05). LI BFR exercise also induced greater decrements in the linear slope coefficient of the regression lines between motor unit recruitment threshold and firing rate (BFR: –165.1±120.4 vs. non-BFR: –44.4±33.1%, p<0.05). Finally, there was a notable shift towards higher values of firing rate and MUAP amplitude post-LI BFR exercise. Taken together, our data indicate that LI BFR exercise increases the activity of motor units with higher MUAP amplitude. They also indicate that motor units with similar MUAP amplitudes become activated at higher firing rates post-LI BFR exercise.

Intrafibre distribution of succinate dehydrogenase in cat tibialis anterior motor units

1992 ◽  
Vol 70 (7) ◽  
pp. 970-976 ◽  
Author(s):  
Thomas P. Martin ◽  
V. R. Edgerton
Keyword(s):  
Mechanical Properties ◽  
Enzymatic Activity ◽  
Succinate Dehydrogenase ◽  
Dehydrogenase Activity ◽  
Tibialis Anterior ◽  
Radial Distance ◽  
Motor Units ◽  
Computer Assisted ◽  
Mitochondrial Enzymes ◽  
Succinate Dehydrogenase Activity

Using isolated ventral root filament stimulation and glycogen depletion techniques, 14 motor units from the cat tibialis anterior were studied. Based on their mechanical properties, the units were classified as either slow-fatigue resistant, fast-fatigue resistant, fast-fatigue intermediate, or fast-fatigable. Quantitative histochemical and computer assisted image analysis techniques were used to determine the activity of succinate dehydrogenase in a population of fibres in each unit. In addition, the intrafibre distribution of succinate dehydrogenase activity was measured in those same fibres by calculating the enzymatic activity of circumferential layers every 0.5 μm starting from the fibre edge to its centre. It was established that enzymatic activity and radial distance were linearly related in the fibres. A range in succinate dehydrogenase activity (mean coefficient of variation, 29%) was observed among the fibres of a unit. In contrast, the intrafibre distribution of that activity was rather consistent (mean variation, 4%) across the fibres of a unit. Further, the intrafibre distribution was similar among the fibres of units classified as the same type. However, the intrafibre distribution was disparate among the different unit types. These data suggest that the intrafibre distribution of mitochondrial enzymes may contribute to the mechanical properties of a motor unit. In this regard, a hypothesis is proposed that describes how the absolute activity of a mitochondrial enzyme, and the intrafibre distribution of that activity, may interactively contribute to the fatigue resistance of a unit.Key words: mitochondria, quantitative histochemistry, fatigue.

scholarly journals Drills or Plays: Some Social Implications in PE Pedagogy

1998 ◽  
Vol 4 (1) ◽  
pp. 42-48
Author(s):  
Arthur Chi Tak WONG
Keyword(s):  
Mechanical Properties ◽  
Teacher Education ◽  
Hong Kong ◽  
Time Allocation ◽  
Teaching Practice ◽  
Ability Groups ◽  
The Mean ◽  
Learning Through Play ◽  
Teaching Learning ◽  
Mean Time

LANGUAGE NOTE | Document text in English; abstract also in Chinese.Personal observations and evaluation reports on teaching practice suggest that PE teachers attending training at the Hong Kong Institute of Education (HKIEd) tend to "over teach" in the sense that they talk too much and put too much emphasis on scientific details such as the mechanical properties of a movement. As more time was spent on explanation and other phases of teaching, learning through play in the applying phase was reduced. Observations also indicated that PE teachers tended to use drills rather than plays or modified games to allow pupils to acquire the criteria performance. A study of 250 lesson plans written by 24 students of an Advanced Certificate of Teacher Education (ACTE) course and 30 students of a Teacher Certificate (TC) course in the HKIEd has also revealed the same tendency. Evidence indicates that the mean time allocation for the applying phase shown by these students is lower than that suggested by textbooks/documents in pedagogy (approximately 50%). "Over teaching" in the above sense may be a socio-political measure in response to the academic movement of our discipline. Drills, which in general facilitate skill refinement, neglect the interest of different ability groups and the two sexes.根據個人觀察及學生實習教學評估報告所得，香港教育學院體育系學生在實習教學時，一般傾向於「過度講授」，在學習前期花太多時間於某些運動科學知識上(例如某些技巧的力學原理)，由於教學上用於講解及其他環節佔用了大部分時間，「技術應用」的機會相應減少。觀察所得亦同時指出，學生在實習教學時亦較喜歡用「操演」的形式，多於讓學生透過實演或模擬遊戲去鞏固有關技術。作者分析24名資深教育証書課程(ACTE)及30名二年制教師証書課程(TC)學生所寫的250份教案，發現學生在課堂上編配予「技術應用」這一環節的時間比率，較一般體育教學文獻所建議的爲低(約課堂時間的50%)。「過度講授」可能是體育界對體育學術化的反響。「操演」有利於技巧的提升，但是忽略了不同技術能力組別及男女之間的興趣差異。

Physiological and histochemical characteristics of motor units in cat tibialis anterior and extensor digitorum longus muscles

1980 ◽  
Vol 43 (6) ◽  
pp. 1615-1630 ◽  
Author(s):  
R. P. Dum ◽  
T. T. Kennedy
Keyword(s):  
Motor Unit ◽  
Tibialis Anterior ◽  
Extensor Digitorum Longus ◽  
Motor Units ◽  
Input Resistance ◽  
Histochemical Staining ◽  
Glycogen Depletion ◽  
Single Motor Units ◽  
The Mean ◽  
Tetanic Tension

1. Intracellular recording and stimulation techniques were used to study the normal motor-unit population of tibialis anterior (TA) and extensor digitorum longus (EDL) muscles in the cat. Histochemical staining of the whole muscle and glycogen depletion of single motor units were performed. These results may be compared to those of their extensor antagonist, medial gastrocnemius (MG), as reported in studies by Burke and co-workers (7, 11, 13). 2. On the basis of two physiological properties, “sag” and fatigue resistance, the motor units in both TA and EDL could be classified into the same categories (types FF, F(int), FR, and S) as in MG (11). In contrast to MG, TA and EDL had nearly twice as many type-FR motor units and only half as many type-S motor units. 3. Glycogen depletion of representative single motor units of types FF and FR suggests a close correspondence between the physiological classification and a unique histochemical profile. No type-S units were depleted. 4. On the basis of histochemical staining, the muscle fibers in TA were presumed to belong to type-FF, -FR, or -S motor units. TA had a higher proportion of type-FR and a lower proportion of type-S muscle fibers than are found in MG. A striking feature was the variation in the proportion of each fiber type in different regions of TA. The anterolateral portion had mostly types FF and FR, while the posteriomedial portion had more types FR and S. 5. The twitch time to peak (TwTP) of isometric motor-unit contractions was generally quite fast with none having TwTP greater than 55 ms. The mean TwTP (not in EDL) and the mean tetanic tension of each motor-unit type were significantly different from each other. Most of the motor units exhibited significant postetanic potentiation of twitch tension and a corresponding lengthening of half-relaxation time and to a lesser degree, twitch contraction time. 6. There was a significant relationship between the inverse of motoneuronal input resistance and either tetanic tension or twitch contraction time. These relationships were not apparent when axonal conduction velocity rather than input resistance was used as an index of motoneuron size. The mean input resistances of the three major motor-unit types were significantly different while the mean conduction velocities of types FF and FR were nearly identical. A weak positive correlation was observed between the TwTP and the afterhyperpolarization of TA and EDL motoneurons. 7. In general, the mechanical characteristics and intrinsic motoneuronal properties of TA and EDL appear to parallel the organization of their extensor antagonist, MG, with some important quantitative differences that may reflect their different functional roles.

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