scholarly journals Effect of synchronization of firings of different motor unit types on the force variability in a model of the rat medial gastrocnemius muscle

2021 ◽  
Vol 17 (4) ◽  
pp. e1008282
Author(s):  
Rositsa Raikova ◽  
Vessela Krasteva ◽  
Piotr Krutki ◽  
Hanna Drzymała-Celichowska ◽  
Katarzyna Kryściak ◽  
...  
Keyword(s):  
Root Mean Square ◽  
Gastrocnemius Muscle ◽  
Muscle Force ◽  
Time Window ◽  
Medial Gastrocnemius ◽  
Force Variability ◽  
Mean Square ◽  
Synchronization Index ◽  
The Mean ◽  
Medial Gastrocnemius Muscle

The synchronized firings of active motor units (MUs) increase the oscillations of muscle force, observed as physiological tremors. This study aimed to investigate the effects of synchronizing the firings within three types of MUs (slow—S, fast resistant to fatigue–FR, and fast fatigable–FF) on the muscle force production using a mathematical model of the rat medial gastrocnemius muscle. The model was designed based on the actual proportion and physiological properties of MUs and motoneurons innervating the muscle. The isometric muscle and MU forces were simulated by a model predicting non-synchronized firing of a pool of 57 MUs (including 8 S, 23 FR, and 26 FF) to ascertain a maximum excitatory signal when all MUs were recruited into the contraction. The mean firing frequency of each MU depended upon the twitch contraction time, whereas the recruitment order was determined according to increasing forces (the size principle). The synchronization of firings of individual MUs was simulated using four different modes and inducing the synchronization of firings within three time windows (± 2, ± 4, and ± 6 ms) for four different combinations of MUs. The synchronization was estimated using two parameters, the correlation coefficient and the cross-interval synchronization index. The four scenarios of synchronization increased the values of the root-mean-square, range, and maximum force in correlation with the increase of the time window. Greater synchronization index values resulted in higher root-mean-square, range, and maximum of force outcomes for all MU types as well as for the whole muscle output; however, the mean spectral frequency of the forces decreased, whereas the mean force remained nearly unchanged. The range of variability and the root-mean-square of forces were higher for fast MUs than for slow MUs; meanwhile, the relative values of these parameters were highest for slow MUs, indicating their important contribution to muscle tremor, especially during weak contractions.

scholarly journals Effect of synchronization of firings of different motor unit types on the force variability in a model of the rat medial gastrocnemius muscle

2020 ◽  
Author(s):  
Rositsa Raikova ◽  
Vessela Krasteva ◽  
Piotr Krutki ◽  
Hanna Drzymała-Celichowska ◽  
Katarzyna Kryściak ◽  
...  
Keyword(s):  
Root Mean Square ◽  
Gastrocnemius Muscle ◽  
Motor Units ◽  
Medial Gastrocnemius ◽  
Force Variability ◽  
Mean Square ◽  
Synchronization Index ◽  
The Mean ◽  
Whole Muscle ◽  
Medial Gastrocnemius Muscle

AbstractOscillations of muscle force, observed as physiological tremors, rely upon the synchronized firings of active motor units (MUs). This study aimed to investigate the effects of synchronizing the firings of three types of MUs on force development using a mathematical model of the rat medial gastrocnemius muscle. The model was designed based on the actual proportion and physiological properties of MUs and motoneurons innervating the muscle. The isometric muscle and MU forces were simulated by a model predicting non-synchronized firing of a pool of 57 MUs (including eight slow, 23 fast resistant to fatigue, and 26 fast fatigable) to ascertain a maximum excitatory signal when all MUs were recruited into the contraction. The mean firing frequency of each MU depended upon the twitch contraction time, whereas the recruitment order was determined according to increasing forces (the size principle). The synchronization of firings of individual MUs was simulated using four different modes and inducing the synchronization of firings within three time windows (± 2, ± 4, and ± 6 ms) for four different combinations of MUs. The synchronization was estimated using two parameters, the correlation coefficient and the cross-interval synchronization index. The four scenarios of synchronization increased the values of the root-mean-square, range, and maximum force in correlation with the increase of the time window. Greater synchronization index values resulted in higher root-mean-square, range, and maximum of force outcomes for all MU types as well as for the whole muscle output; however, the mean spectral frequency of the forces decreased, whereas the mean force remained nearly unchanged. The range of variability and the root-mean-square of forces were higher for fast MUs than for slow MUs; meanwhile, the relative values of these parameters were highest for slow MUs, indicating their important contribution to muscle tremor, especially during weak contractions.Author summaryThe synchronization of firings of motor units (MUs), the smallest functional elements of skeletal muscle increases fluctuations in muscle force, known as physiological tremor, which can disturb high-precision movements. In this study, we adopted a recently proposed muscle model consisting of MUs of three different types (fast fatigable, fast resistant to fatigue, and slow) to study four different scenarios of MU synchronization during a steady level of excitatory input to motoneurons. The discharge patterns were synchronized between pairs of MUs by shifting in time individual pulses, which occurred within a short time interval, and a degree of synchronization was then estimated. The increased synchronization index resulted in increased force variability for all MU types as well as for the whole muscle output; however, the mean force levels remained nearly unchanged, whereas the frequencies of the force oscillations were decreased. The absolute range of force variability was higher for fast than for slow MUs, indicating their dominant influence on muscle tremor at strong contractions, but the highest relative increase in force variability was observed for synchronized slow MUs, indicating their significant contribution to tremor during weak contractions, in which only slow MUs are active.

scholarly journals A model of the rat medial gastrocnemius muscle based on inputs to motoneurons and on an algorithm for prediction of the motor unit force

2018 ◽  
Vol 120 (4) ◽  
pp. 1973-1987 ◽  
Author(s):  
R. Raikova ◽  
J. Celichowski ◽  
S. Angelova ◽  
P. Krutki
Keyword(s):  
Motor Unit ◽  
Input Data ◽  
Gastrocnemius Muscle ◽  
Muscle Force ◽  
Motor Units ◽  
Contractile Properties ◽  
Medial Gastrocnemius ◽  
Physiological Data ◽  
Excitation Signal ◽  
Medial Gastrocnemius Muscle

The muscle force is the sum of forces of multiple motor units (MUs), which have different contractile properties. During movements, MUs develop unfused tetani, which result from summation of twitch-shape responses to individual stimuli, which are variable in amplitude and duration. The aim of the study was to develop a realistic muscle model that would integrate previously developed models of MU contractions and an algorithm for the prediction of tetanic forces. The proposed model of rat medial gastrocnemius muscle is based on physiological data: excitability and firing frequencies of motoneurons, contractile properties, and the number and proportion of MUs in the muscle. The MU twitches were modeled by a six-parameter analytical function. The excitability of motoneurons was modeled according to a distribution of their rheobase currents measured experimentally. Processes of muscle force regulation were modeled according to a common drive hypothesis. The excitation signal to motoneurons was modeled by two form types: triangular and trapezoid. The discharge frequencies of MUs, calculated individually for each MU, corresponded to those recorded for rhythmic firing of motoneurons. The force of the muscle was calculated as the sum of all recruited MUs. Participation of the three types of MUs in the developed muscle force was presented at different levels of the excitation signal to motoneurons. The model appears highly realistic and open for input data from various skeletal muscles with different compositions of MU types. The results were compared with three other models with different distribution of the input parameters.NEW & NOTEWORTHY The proposed mathematical model of rat medial gastrocnemius muscle is highly realistic because it is based strictly on experimentally determined motor unit contractile parameters and motoneuron properties. It contains the actual number and proportion of motor units and takes into consideration their different contributions to the whole muscle force, depending on the level of the excitation signal. The model is open for input data from other muscles, and additional physiological parameters can also be included.

The effect of long-term immobilization on the motor unit population of the cat medial gastrocnemius muscle

Neuroscience ◽  
1981 ◽  
Vol 6 (4) ◽  
pp. 725-739 ◽  
Author(s):  
R.F. Mayer ◽  
R.E. Burke ◽  
J. Toop ◽  
J.A. Hodgson ◽  
K. Kanda ◽  
...  
Keyword(s):  
Motor Unit ◽  
Gastrocnemius Muscle ◽  
Medial Gastrocnemius ◽  
Medial Gastrocnemius Muscle

Voluntary control of forward leaning posture relates to low-frequency neural inputs to the medial gastrocnemius muscle

2019 ◽  
Vol 68 ◽  
pp. 187-192 ◽  
Author(s):  
Tatsunori Watanabe ◽  
Ippei Nojima ◽  
Hideshi Sugiura ◽  
Basma Yacoubi ◽  
Evangelos A. Christou
Keyword(s):  
Gastrocnemius Muscle ◽  
Low Frequency ◽  
Voluntary Control ◽  
Medial Gastrocnemius ◽  
Medial Gastrocnemius Muscle

Activity and motor unit size in partially denervated rat medial gastrocnemius

1994 ◽  
Vol 76 (6) ◽  
pp. 2663-2671 ◽  
Author(s):  
L. J. Einsiedel ◽  
A. R. Luff
Keyword(s):  
Motor Unit ◽  
Gastrocnemius Muscle ◽  
Motor Units ◽  
Ventral Root ◽  
Treadmill Walking ◽  
Medial Gastrocnemius ◽  
Unit Size ◽  
Partial Denervation ◽  
Motoneuron Activity ◽  
Medial Gastrocnemius Muscle

The aim of the study was to determine whether increased motoneuron activity induced by treadmill walking would alter the extent of motoneuron sprouting in the partially denervated rat medial gastrocnemius muscle. An extensive partial denervation was effected by unilateral section of the L5 ventral root, and it is very likely that all units remaining in the medial gastrocnemius were used in treadmill walking. Rats were trained for 1.5 h/day and after 14 days were walking at least 1 km/day. Motor unit characteristics were determined 24 days after the partial denervation and were compared with units from partially denervated control (PDC) animals and with units from normal (control) animals. In PDC rats, force developed by slow, fast fatigue-resistant, and fast intermediate-fatigable motor units increased substantially compared with control animals; that of fast-fatigable units did not increase. In partially denervated exercised animals, force developed by slow and fast-fatigue-resistant units showed no further increase, but fast-intermediate- and fast-fatigable units showed significant increases compared with those in PDC animals. The changes in force were closely paralleled by changes in innervation ratios. We concluded that neuronal activity is an important factor in determining the rate of motoneuron sprouting.

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