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The synchronized firings of active motor units (MUs) increase the oscillations of muscle force, observed as physiological tremor. 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.
Rositsa Raikova; Vessela Krasteva; Piotr Krutki; Hanna Drzymała-Celichowska; Katarzyna Kryściak; Jan Celichowski. Effect of synchronization of firings of different motor unit types on the force variability in a model of the rat medial gastrocnemius muscle. PLOS Computational Biology 2021, 17, e1008282 .
AMA StyleRositsa Raikova, Vessela Krasteva, Piotr Krutki, Hanna Drzymała-Celichowska, Katarzyna Kryściak, Jan Celichowski. Effect of synchronization of firings of different motor unit types on the force variability in a model of the rat medial gastrocnemius muscle. PLOS Computational Biology. 2021; 17 (4):e1008282.
Chicago/Turabian StyleRositsa Raikova; Vessela Krasteva; Piotr Krutki; Hanna Drzymała-Celichowska; Katarzyna Kryściak; Jan Celichowski. 2021. "Effect of synchronization of firings of different motor unit types on the force variability in a model of the rat medial gastrocnemius muscle." PLOS Computational Biology 17, no. 4: e1008282.
Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of largely unknown pathophysiology, characterized by the progressive loss of motoneurons (MNs). We review data showing that in presymptomatic ALS mice, MNs display reduced intrinsic excitability and impaired level of excitatory inputs. The loss of repetitive firing specifically affects the large MNs innervating fast contracting muscle fibers, which are the most vulnerable MNs in ALS. Interventions that aimed at restoring either the intrinsic excitability or the synaptic excitation result in a decrease of disease markers in MNs and delayed neuromuscular junction denervation. We then focus on trans‐spinal direct current stimulation (tsDCS), a noninvasive tool, since it modulates the activity of spinal neurons and networks. Effects of tsDCS depend on the polarity of applied current. Recent work shows that anodal tsDCS induces long‐lasting enhancement of MN excitability and synaptic excitation of spinal MNs. Moreover, we show preliminary results indicating that anodal tsDCS enhances the excitatory synaptic inputs to MNs in ALS mice. In conclusion, we suggest that chronic application of anodal tsDCS might be useful as a complementary method in the management of ALS patients.
Marcin Bączyk; Piotr Krutki; Daniel Zytnicki. Is there hope that transpinal direct current stimulation corrects motoneuron excitability and provides neuroprotection in amyotrophic lateral sclerosis? Physiological Reports 2021, 9, e14706 .
AMA StyleMarcin Bączyk, Piotr Krutki, Daniel Zytnicki. Is there hope that transpinal direct current stimulation corrects motoneuron excitability and provides neuroprotection in amyotrophic lateral sclerosis? Physiological Reports. 2021; 9 (2):e14706.
Chicago/Turabian StyleMarcin Bączyk; Piotr Krutki; Daniel Zytnicki. 2021. "Is there hope that transpinal direct current stimulation corrects motoneuron excitability and provides neuroprotection in amyotrophic lateral sclerosis?" Physiological Reports 9, no. 2: e14706.
The study aimed to provide evidence on the impact of indoor cycling (IC) in reducing cardiometabolic risk factors. The study compares the effects of a 3 month IC program involving three 55 min sessions per week on women aged 40–60 years, with obesity (OW, n = 18) vs. women with normal body weight (NW, n = 8). At baseline and at the end of the study, anthropometric parameters, oxygen uptake (VO2 peak), and serum parameters: glucose, total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and triglycerides (TG), insulin, human anti-oxidized low-density lipoprotein antibody (OLAb), total blood antioxidant capacity (TAC), thiobarbituric acid reactive substances (TBARS), endothelial nitric oxide synthase (eNOS), C-reactive protein (CRP), lipid accumulation product (LAP), and homeostasis model assessment of insulin resistance index (HOMA IR) were determined. Before the intervention, VO2 peak and HDL-C levels were significantly lower and levels of TG, LAP, insulin, HOMA-IR, and CRP were significantly higher in the OW group compared to those in the NW group. After the intervention, only the OW group saw a decrease in body mass, total cholesterol, OLAb, TBARS, and CRP concentration and an increase in total body skeletal muscle mass and HDL-C concentration. In response to the IC training, measured indicators in the OW group were seen to approach the recommended values, but all between-group differences remained significant. Our results demonstrate that IC shows promise for reducing cardiometabolic risk factors, especially dyslipidemia. After 12 weeks of regular IC, the metabolic function of the OW group adapted in many aspects to be more like that of the NW group.
Marzena Ratajczak; Damian Skrypnik; Piotr Krutki; Joanna Karolkiewicz. Effects of an Indoor Cycling Program on Cardiometabolic Factors in Women with Obesity vs. Normal Body Weight. International Journal of Environmental Research and Public Health 2020, 17, 8718 .
AMA StyleMarzena Ratajczak, Damian Skrypnik, Piotr Krutki, Joanna Karolkiewicz. Effects of an Indoor Cycling Program on Cardiometabolic Factors in Women with Obesity vs. Normal Body Weight. International Journal of Environmental Research and Public Health. 2020; 17 (23):8718.
Chicago/Turabian StyleMarzena Ratajczak; Damian Skrypnik; Piotr Krutki; Joanna Karolkiewicz. 2020. "Effects of an Indoor Cycling Program on Cardiometabolic Factors in Women with Obesity vs. Normal Body Weight." International Journal of Environmental Research and Public Health 17, no. 23: 8718.
Recently, it has been shown that spinal cord polarization considerably modulates motoneuron activity, with certain observed changes in motoneuron membrane and firing properties outlasting the duration of polarization. The purpose of this study was to determine whether repeated sessions of transcutaneous transspinal direct current stimulation (tsDCS) induce adaptive changes in motoneuron properties. In this study, adult male Wistar rats under isoflurane anesthesia were subjected to anodal (n=6) or cathodal (n=6) tsDCS (100 uA, 15 min) 5 days per week for 5 weeks. Sham control group rats (n=6) served as a reference. Intracellular recordings from lumbar spinal motoneurons were performed under pentobarbital anesthesia one day after the final tsDCS session to analyze membrane and firing properties. Anodal polarization appeared to be effective in evoking significant adaptive changes toward the facilitation of motoneuron firing. When compared to the sham polarization group, these adaptations were expressed by the increased input resistance (P=0.0077), decreased voltage threshold for spike generation (P=0.0248) and doublet threshold (P=0.0311), increased maximum SSF frequency (P=0.0073), SSF frequency range (P=0.0075), and slope of the frequency-current relationship (P=0.0111). However, the effects of cathodal polarization were modest and generally not significant in regard to the sham control. These novel findings support the existing knowledge on alterations in spinal neuronal network excitability in response to polarization and provide the direct evidence of adaptive neuroplasticity of spinal motoneurons in response to chronically applied tsDCS.
Marcin Bączyk; Hanna Drzymała-Celichowska; Włodzimierz Mrówczyński; Piotr Krutki. Polarity-dependent adaptations of motoneuron electrophysiological properties after 5-week transcutaneous spinal direct current stimulation in rats. Journal of Applied Physiology 2020, 129, 1 .
AMA StyleMarcin Bączyk, Hanna Drzymała-Celichowska, Włodzimierz Mrówczyński, Piotr Krutki. Polarity-dependent adaptations of motoneuron electrophysiological properties after 5-week transcutaneous spinal direct current stimulation in rats. Journal of Applied Physiology. 2020; 129 (4):1.
Chicago/Turabian StyleMarcin Bączyk; Hanna Drzymała-Celichowska; Włodzimierz Mrówczyński; Piotr Krutki. 2020. "Polarity-dependent adaptations of motoneuron electrophysiological properties after 5-week transcutaneous spinal direct current stimulation in rats." Journal of Applied Physiology 129, no. 4: 1.
Oscillations 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.
Rositsa Raikova; Vessela Krasteva; Piotr Krutki; Hanna Drzymała-Celichowska; Katarzyna Kryściak; Jan Celichowski. Effect of synchronization of firings of different motor unit types on the force variability in a model of the rat medial gastrocnemius muscle. 2020, 1 .
AMA StyleRositsa Raikova, Vessela Krasteva, Piotr Krutki, Hanna Drzymała-Celichowska, Katarzyna Kryściak, Jan Celichowski. Effect of synchronization of firings of different motor unit types on the force variability in a model of the rat medial gastrocnemius muscle. . 2020; ():1.
Chicago/Turabian StyleRositsa Raikova; Vessela Krasteva; Piotr Krutki; Hanna Drzymała-Celichowska; Katarzyna Kryściak; Jan Celichowski. 2020. "Effect of synchronization of firings of different motor unit types on the force variability in a model of the rat medial gastrocnemius muscle." , no. : 1.
Thus far, the differences in effect of auditory or visual feedback in motor learning have presented results derived from mixed groups and sex differences have not been considered. However, perception and processing of auditory stimuli and performance of visual motor tasks appear to be sex-related. The purpose of this study was to investigate the learning of the simple motor task of maintaining a requested handgrip force in separate male and female groups. A total of 31 volunteers (15 males, 16 females) were randomly assigned to one of four experimental groups with defined sex and training conditions (audio or visual feedback). Participants performed training sessions over a period of six days, for which auditory or visual feedback was provided, and the effectiveness of both types of signals was compared. The evident learning effect was found in all groups, and the main effect of sex was significant among visual groups in favor of the males (p < 0.05). On the other hand, the main effect of feedback conditions was found to be significant among females, beneficially in the case of auditory displays (p < 0.05). The results lead to the conclusion that an equal number of males and females in mixed experimental groups may be supportive to obtain reliable results. Moreover, in motor-learning studies conducted on females only, a design including auditory feedback would be more suitable.
Jacek Tarnas; Rafał Stemplewski; Piotr Krutki. Sex Differences in Maintaining the Requested Handgrip Force Enhanced by Auditory or Visual Feedback. International Journal of Environmental Research and Public Health 2020, 17, 5158 .
AMA StyleJacek Tarnas, Rafał Stemplewski, Piotr Krutki. Sex Differences in Maintaining the Requested Handgrip Force Enhanced by Auditory or Visual Feedback. International Journal of Environmental Research and Public Health. 2020; 17 (14):5158.
Chicago/Turabian StyleJacek Tarnas; Rafał Stemplewski; Piotr Krutki. 2020. "Sex Differences in Maintaining the Requested Handgrip Force Enhanced by Auditory or Visual Feedback." International Journal of Environmental Research and Public Health 17, no. 14: 5158.
Intracellular recording of spinal motoneurons in vivo provides a “gold standard” for determining the cells’ electrophysiological characteristics in the intact spinal network and holds significant advantages relative to classical in vitro or extracellular recording techniques. An advantage of in vivo intracellular recordings is that this method can be performed on adult animals with a fully mature nervous system, and therefore many observed physiological mechanisms can be translated to practical applications. In this methodological paper, we describe this procedure combined with externally applied constant current stimulation, which mimics polarization processes occurring within spinal neuronal networks. Trans-spinal direct current stimulation (tsDCS) is an innovative method increasingly used as a neuromodulatory intervention in rehabilitation after various neurological injuries as well as in sports. The influence of tsDCS on the nervous system remains poorly understood and the physiological mechanisms behind its actions are largely unknown. The application of the tsDCS simultaneously with intracellular recordings enables us to directly observe changes of motoneuron membrane properties and characteristics of rhythmic firing in response to the polarization of the spinal neuronal network, which is crucial for the understanding of tsDCS actions. Moreover, when the presented protocol includes the identification of the motoneuron with respect to an innervated muscle and its function (flexor versus extensor) as well as the physiological type (fast versus slow) it provides an opportunity to selectively investigate the influence of tsDCS on identified components of spinal circuitry, which seem to be differently affected by polarization. The presented procedure focuses on surgical preparation for intracellular recordings and stimulation with an emphasis on the steps which are necessary to achieve preparation stability and reproducibility of results. The details of the methodology of the anodal or cathodal tsDCS application are discussed while paying attention to practical and safety issues.
Marcin Bączyk; Piotr Krutki. In Vivo Intracellular Recording of Type-Identified Rat Spinal Motoneurons During Trans-Spinal Direct Current Stimulation. Journal of Visualized Experiments 2020, e61439 .
AMA StyleMarcin Bączyk, Piotr Krutki. In Vivo Intracellular Recording of Type-Identified Rat Spinal Motoneurons During Trans-Spinal Direct Current Stimulation. Journal of Visualized Experiments. 2020; (159):e61439.
Chicago/Turabian StyleMarcin Bączyk; Piotr Krutki. 2020. "In Vivo Intracellular Recording of Type-Identified Rat Spinal Motoneurons During Trans-Spinal Direct Current Stimulation." Journal of Visualized Experiments , no. 159: e61439.
Trans‐spinal direct current stimulation (tsDCS) is a novel neuromodulatory technique that has been used during neurological rehabilitation and sports to modulate muscle activation. However, the physiological mechanisms that underly the long‐lasting functional effects of polarization are not yet fully understood, nor are their relationships with specific neuronal populations. The acute facilitatory and depressive effects of anodal and cathodal polarization on motoneurons have been recently demonstrated, and the aim of this study was to determine whether tsDCS‐evoked modulations of motoneuron properties are able to persist over several hours. Intracellular recordings from multiple antidromically identified rat motoneurons were performed both before and after the application of tsDCS (0.1 mA for 15 minutes), at various time points up to 180 minutes after the offset of anodal or cathodal tsDCS. The examined effects of anodal polarization included decreased rheobase, voltage threshold, the minimum and maximum currents necessary for rhythmic firing, increased rhythmic firing frequencies, and the slope of the f–I relationship. The majority of these facilitatory changes to threshold and firing properties were sustained for 30 to 60 minutes after polarization. In contrast, the significant effects of cathodal polarization were absent, except the short‐lasting decreased ability for motoneurons to induce rhythmic activity. This study provides direct evidence that a single polarization session can alter the electrophysiological properties of motoneurons for at least one hour and provides a basis for the further use of tsDCS techniques under conditions where the sustained modification of motoneuron firing is desired.
Marcin Bączyk; Hanna Drzymała‐Celichowska; Włodzimierz Mrówczyński; Piotr Krutki. Long‐lasting modifications of motoneuron firing properties by trans‐spinal direct current stimulation in rats. European Journal of Neuroscience 2019, 51, 1743 -1755.
AMA StyleMarcin Bączyk, Hanna Drzymała‐Celichowska, Włodzimierz Mrówczyński, Piotr Krutki. Long‐lasting modifications of motoneuron firing properties by trans‐spinal direct current stimulation in rats. European Journal of Neuroscience. 2019; 51 (8):1743-1755.
Chicago/Turabian StyleMarcin Bączyk; Hanna Drzymała‐Celichowska; Włodzimierz Mrówczyński; Piotr Krutki. 2019. "Long‐lasting modifications of motoneuron firing properties by trans‐spinal direct current stimulation in rats." European Journal of Neuroscience 51, no. 8: 1743-1755.
Spinal polarization evoked by direct current stimulation [trans-spinal direct current stimulation (tsDCS)] is a novel method for altering spinal network excitability; however, it remains not well understood. The aim of this study was to determine whether tsDCS influences spinal motoneuron activity. Twenty Wistar rats under general pentobarbital anesthesia were subjected to 15 min anodal ( n = 10) or cathodal ( n = 10) tsDCS of 0.1 mA intensity, and the electrophysiological properties of their motoneurons were intracellularly measured before, during, and after direct current application. The major effects of anodal intervention included increased minimum firing frequency and the slope of the frequency-current ( f-I) relationship, as well as decreased rheobase and currents evoking steady-state firing (SSF). The effects of cathodal polarization included decreased maximum SSF frequency, decreased f-I slope, and decreased current evoking the maximum SSF. Notably, the majority of observed effects appeared immediately after the current onset, developed during polarization, and outlasted it for at least 15 min. Moreover, the effects of anodal polarization were generally more pronounced and uniform than those evoked by cathodal polarization. Our study is the first to present polarity-dependent, long-lasting changes in spinal motoneuron firing following tsDCS, which may aid in the development of more safe and accurate application protocols in medicine and sport. NEW & NOTEWORTHY Trans-spinal direct current stimulation induces significant polarity-dependent, long-lasting changes in the threshold and firing properties of spinal motoneurons. Anodal polarization potentiates motoneuron firing whereas cathodal polarization acts mainly toward firing inhibition. The alterations in rheobase and rhythmic firing properties are not restricted to the period of current application and can be observed long after the current offset.
Marcin Baczyk; Hanna Drzymala-Celichowska; Włodzimierz Mrówczyński; Piotr Krutki. Motoneuron firing properties are modified by trans-spinal direct current stimulation in rats. Journal of Applied Physiology 2019, 126, 1232 -1241.
AMA StyleMarcin Baczyk, Hanna Drzymala-Celichowska, Włodzimierz Mrówczyński, Piotr Krutki. Motoneuron firing properties are modified by trans-spinal direct current stimulation in rats. Journal of Applied Physiology. 2019; 126 (5):1232-1241.
Chicago/Turabian StyleMarcin Baczyk; Hanna Drzymala-Celichowska; Włodzimierz Mrówczyński; Piotr Krutki. 2019. "Motoneuron firing properties are modified by trans-spinal direct current stimulation in rats." Journal of Applied Physiology 126, no. 5: 1232-1241.
Jan Celichowski; Piotr Krutki. Motor Units and Muscle Receptors. Muscle and Exercise Physiology 2019, 51 -91.
AMA StyleJan Celichowski, Piotr Krutki. Motor Units and Muscle Receptors. Muscle and Exercise Physiology. 2019; ():51-91.
Chicago/Turabian StyleJan Celichowski; Piotr Krutki. 2019. "Motor Units and Muscle Receptors." Muscle and Exercise Physiology , no. : 51-91.
The sag phenomenon can be observed in fast motor units (MUs) as a transitional decline in force during unfused tetanic contractions; however, its mechanisms are poorly understood. The study aimed to identify in the rat muscle factors that contribute to sag in two types of fast MUs: fast fatigable (FF) and fast resistant to fatigue (FR). First, we performed mathematical decomposition of sagging tetanic contractions of FF and FR MUs into twitch-like responses to consecutive stimuli. This process indicated an increase in the amplitudes of a few initial responses (up to the 2nd–3rd for FF and up to the 2nd–7th for FR MUs), followed by a decrease in the amplitudes of later responses. In comparison to the first twitch, the relative increase in force amplitudes of the several subsequent decomposed responses was smaller, and their contraction and relaxation times were shorter for FF than for FR units, which corresponded to observed differences in their sag profiles. Additionally, after occlusion of the blood circulation, sag disappeared, but it reappeared after restoration of the blood supply. This indicates that the presence of sag depends on the proper circulation in the muscle.
K. Kryściak; Jan Celichowski; P. Krutki; R. Raikova; H. Drzymała-Celichowska. Factors contributing to sag in unfused tetanic contractions of fast motor units in rat medial gastrocnemius. Journal of Electromyography and Kinesiology 2018, 44, 70 -77.
AMA StyleK. Kryściak, Jan Celichowski, P. Krutki, R. Raikova, H. Drzymała-Celichowska. Factors contributing to sag in unfused tetanic contractions of fast motor units in rat medial gastrocnemius. Journal of Electromyography and Kinesiology. 2018; 44 ():70-77.
Chicago/Turabian StyleK. Kryściak; Jan Celichowski; P. Krutki; R. Raikova; H. Drzymała-Celichowska. 2018. "Factors contributing to sag in unfused tetanic contractions of fast motor units in rat medial gastrocnemius." Journal of Electromyography and Kinesiology 44, no. : 70-77.
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.
Rositsa Raikova; Jan Celichowski; Silvija Angelova; Piotr Krutki. A model of the rat medial gastrocnemius muscle based on inputs to motoneurons and on an algorithm for prediction of the motor unit force. Journal of Neurophysiology 2018, 120, 1973 -1987.
AMA StyleRositsa Raikova, Jan Celichowski, Silvija Angelova, Piotr Krutki. A model of the rat medial gastrocnemius muscle based on inputs to motoneurons and on an algorithm for prediction of the motor unit force. Journal of Neurophysiology. 2018; 120 (4):1973-1987.
Chicago/Turabian StyleRositsa Raikova; Jan Celichowski; Silvija Angelova; Piotr Krutki. 2018. "A model of the rat medial gastrocnemius muscle based on inputs to motoneurons and on an algorithm for prediction of the motor unit force." Journal of Neurophysiology 120, no. 4: 1973-1987.
This study aimed at investigating the effects of 2, 4 and 8 weeks of endurance training on the contractile properties of slow (S), fast fatigue resistant (FR) and fast fatigable (FF) motor units (MUs) in rat medial gastrocnemius (MG) in relation to the changes in muscle mitochondrial biogenesis. The properties of functionally isolated MUs were examined in vivo. Mitochondrial biogenesis was judged based on the changes in mitochondrial DNA copy number (mtDNA), the content of the electron transport chain (ETC) proteins and PGC-1α in the MG. Moreover, the markers of mitochondria remodeling mitofusins (Mfn1, Mfn2) and dynamin-like protein (Opa1) were studied using qPCR. A proportion of FR MUs increased from 37.9% to 50.8% and a proportion of FF units decreased from 44.7% to 26.6% after 8 weeks of training. The increased fatigue resistance, shortened twitch duration, and increased ability to potentiate force were found as early as after 2 weeks of endurance training, predominantly in FR MUs. Moreover, just after 2 weeks of the training an enhancement of the mitochondrial network remodeling was present as judged by an increase in expression of Mfn1, Opa1 and an increase in PGC-1α in the slow part of MG. Interestingly, no signs of intensification of mitochondrial biogenesis assessed by ETC proteins content and mtDNA in slow and fast parts of gastrocnemius were found at this stage of the training. Nevertheless, after 8 weeks of training an increase in the ETC protein content was observed, but mainly in the slow part of gastrocnemius. Concluding, the functional changes in MUs' contractile properties leading to the enhancement of muscle performance accompanied by an activation of signalling that controls the muscle mitochondrial network reorganisation and mitochondrial biogenesis belong to an early muscle adaptive responses that precede an increase in mitochondrial ETC protein content.
Katarzyna Kryściak; Joanna Majerczak; Jakub Kryściak; Dawid Łochyński; Dominik Kaczmarek; Hanna Drzymała-Celichowska; Piotr Krutki; Anna Gawedzka; Magdalena Guzik; Michal Korostynski; Zbigniew Szkutnik; Elżbieta Pyza; Wiesława Jarmuszkiewicz; Jerzy A. Zoladz; Jan Celichowski. Adaptation of motor unit contractile properties in rat medial gastrocnemius to treadmill endurance training: Relationship to muscle mitochondrial biogenesis. PLOS ONE 2018, 13, e0195704 .
AMA StyleKatarzyna Kryściak, Joanna Majerczak, Jakub Kryściak, Dawid Łochyński, Dominik Kaczmarek, Hanna Drzymała-Celichowska, Piotr Krutki, Anna Gawedzka, Magdalena Guzik, Michal Korostynski, Zbigniew Szkutnik, Elżbieta Pyza, Wiesława Jarmuszkiewicz, Jerzy A. Zoladz, Jan Celichowski. Adaptation of motor unit contractile properties in rat medial gastrocnemius to treadmill endurance training: Relationship to muscle mitochondrial biogenesis. PLOS ONE. 2018; 13 (4):e0195704.
Chicago/Turabian StyleKatarzyna Kryściak; Joanna Majerczak; Jakub Kryściak; Dawid Łochyński; Dominik Kaczmarek; Hanna Drzymała-Celichowska; Piotr Krutki; Anna Gawedzka; Magdalena Guzik; Michal Korostynski; Zbigniew Szkutnik; Elżbieta Pyza; Wiesława Jarmuszkiewicz; Jerzy A. Zoladz; Jan Celichowski. 2018. "Adaptation of motor unit contractile properties in rat medial gastrocnemius to treadmill endurance training: Relationship to muscle mitochondrial biogenesis." PLOS ONE 13, no. 4: e0195704.
Resistance training, with repeated short-term and high-intensity exercises, is responsible for an increase in muscle mass and force. The aim of this study was to determine whether such training induces adaptations in the electrophysiological properties of motoneurons innervating the trained muscles and to relate these adaptive changes to previous observations made on motor unit contractile properties. The study was performed on adult male Wistar rats. Animals from the training group were subjected to a 5-wk voluntary progressive weight-lifting program, whereas control rats were restricted to standard cage activity. Intracellular recordings from lumbar spinal motoneurons were made under pentobarbital anesthesia. Membrane properties were measured, and rhythmic firing of motoneurons was analyzed. Strength training evoked adaptive changes in both slow- and fast-type motoneurons, indicating their increased excitability. A shorter spike duration, a higher input resistance, a lower rheobase, a decrease in the minimum current required to evoke rhythmic firing, an increase in the maximum frequencies of the early-state firing (ESF) and the steady-state firing (SSF), and an increase in the respective slopes of the frequency-current ( f/ I) relationship were observed in fast motoneurons of the trained group. The increase in the maximum ESF and SSF frequencies and an increase in the SSF f/ I slope were also present in slow motoneurons. Higher maximum firing rates of motoneurons as well as higher discharge frequencies evoked at the same level of intracellular depolarization current imply higher levels of tetanic forces developed by motor units over the operating range of force production after strength training. NEW & NOTEWORTHY Neuronal responses to weight-lifting training can be observed in altered properties of both slow and fast motoneurons. Motoneurons of trained animals are more excitable, require lower intracellular currents to evoke rhythmic firing, and have the ability to evoke higher maximum discharge frequencies during repetitive firing.
Piotr Krutki; Włodzimierz Mrówczyński; Marcin Bączyk; Dawid Łochyński; Jan Celichowski. Adaptations of motoneuron properties after weight-lifting training in rats. Journal of Applied Physiology 2017, 123, 664 -673.
AMA StylePiotr Krutki, Włodzimierz Mrówczyński, Marcin Bączyk, Dawid Łochyński, Jan Celichowski. Adaptations of motoneuron properties after weight-lifting training in rats. Journal of Applied Physiology. 2017; 123 (3):664-673.
Chicago/Turabian StylePiotr Krutki; Włodzimierz Mrówczyński; Marcin Bączyk; Dawid Łochyński; Jan Celichowski. 2017. "Adaptations of motoneuron properties after weight-lifting training in rats." Journal of Applied Physiology 123, no. 3: 664-673.
An unfused tetanus of a motor unit (MU) evoked by a train of pulses at variable interpulse intervals is the sum of non-equal twitch-like responses to these stimuli. A tool for a precise prediction of these successive contractions for MUs of different physiological types with different contractile properties is crucial for modeling the whole muscle behavior during various types of activity. The aim of this paper is to develop such a general mathematical algorithm for the MUs of the medial gastrocnemius muscle of rats. For this purpose, tetanic curves recorded for 30 MUs (10 slow, 10 fast fatigue-resistant and 10 fast fatigable) were mathematically decomposed into twitch-like contractions. Each contraction was modeled by the previously proposed 6-parameter analytical function, and the analysis of these six parameters allowed us to develop a prediction algorithm based on the following input data: parameters of the initial twitch, the maximum force of a MU and the series of pulses. Linear relationship was found between the normalized amplitudes of the successive contractions and the remainder between the actual force levels at which the contraction started and the maximum tetanic force. The normalization was made according to the amplitude of the first decomposed twitch. However, the respective approximation lines had different specific angles with respect to the ordinate. These angles had different and non-overlapping ranges for slow and fast MUs. A sensitivity analysis concerning this slope was performed and the dependence between the angles and the maximal fused tetanic force normalized to the amplitude of the first contraction was approximated by a power function. The normalized MU contraction and half-relaxation times were approximated by linear functions depending on the normalized actual force levels at which each contraction starts. The normalization was made according to the contraction time of the first contraction. The actual force levels were calculated initially from the recorded tetanic curves and subsequently from the modeled curves obtained from the summation of all models of the preceding contractions (the so called “full prediction”). The preciseness of the prediction was verified by two coefficients estimating the error between the modeled and the experimentally recorded curves. The proposed approach was tested for 30 MUs from the database and for three additional MUs, not included in the initial set. It was concluded that this general algorithm can be successfully used for modeling of a unfused tetanus course of a single MU of fast and slow type.
Rositsa Raikova; Piotr Krutki; Jan Celichowski. A General Mathematical Algorithm for Predicting the Course of Unfused Tetanic Contractions of Motor Units in Rat Muscle. PLOS ONE 2016, 11, e0162385 .
AMA StyleRositsa Raikova, Piotr Krutki, Jan Celichowski. A General Mathematical Algorithm for Predicting the Course of Unfused Tetanic Contractions of Motor Units in Rat Muscle. PLOS ONE. 2016; 11 (9):e0162385.
Chicago/Turabian StyleRositsa Raikova; Piotr Krutki; Jan Celichowski. 2016. "A General Mathematical Algorithm for Predicting the Course of Unfused Tetanic Contractions of Motor Units in Rat Muscle." PLOS ONE 11, no. 9: e0162385.
Effects of the summation of forces generated by functionally isolated slow-twitch motor units (MU) of the rat soleus muscle were examined in this study. Initially, the twitch, fused tetanic and unfused tetanic contractions evoked by trains of stimuli at variable interpulse intervals were recorded for each MU. Then, two, three or four MUs were co-activated, and the recorded forces were compared to the algebraic sum of the forces of individual MUs. The mean cumulative force of twitches and the mean cumulative force of fused tetani were not statistically different from the respective algebraic sums of forces, which revealed a high degree of linearity in the summation. However, relaxation of the recorded tetanic contractions (either fused or unfused) was faster than that predicted by the linear summation of individual contractions. Moreover, for twitch and tetanic contractions, a tendency to shorten relaxation with an increasing number of co-active MUs was noted. The results indicate that forces of rat soleus slow MUs sum up more linearly than in the respective cat muscle as well as more linearly than for fast MUs in the medial gastrocnemius muscle.
Hanna Drzymała-Celichowska; Piotr Kaczmarek; Piotr Krutki; Jan Celichowski. Summation of slow motor unit forces at constant and variable interpulse intervals in rat soleus muscle. Journal of Electromyography and Kinesiology 2016, 30, 1 -8.
AMA StyleHanna Drzymała-Celichowska, Piotr Kaczmarek, Piotr Krutki, Jan Celichowski. Summation of slow motor unit forces at constant and variable interpulse intervals in rat soleus muscle. Journal of Electromyography and Kinesiology. 2016; 30 ():1-8.
Chicago/Turabian StyleHanna Drzymała-Celichowska; Piotr Kaczmarek; Piotr Krutki; Jan Celichowski. 2016. "Summation of slow motor unit forces at constant and variable interpulse intervals in rat soleus muscle." Journal of Electromyography and Kinesiology 30, no. : 1-8.
Slow motor units (MUs) have no sag in their unfused tetani. This study in anesthetized rats shows that the sag can be observed in slow soleus MUs after prolonged activity. Twitches and unfused tetanic contractions were recorded from male (n=35) and female (n=39) MUs before and after the four minutes of the fatigue test (trains of 13 pulses at 40 Hz repeated every second). After this activity twitch contractions potentiated and a shift in the steep part of the force-frequency curve towards lower frequencies was observed in both sexes. Initially no sag was visible in unfused tetani, but after the fatigue test the phenomenon was observed in 77% of male, while in 13% of female MUs, the result consistent with the previously reported higher content of IIa myosin and faster contraction of MUs in male soleus. The decomposition of tetani with sag into trains of twitch-shape responses to consecutive stimuli revealed higher forces of initial decomposed twitches than later. The revealed alterations the force development due to long-lasting activation of slow MUs were sex-related and more pronounced in male soleus.
Hanna Drzymała-Celichowska; Rositsa Raikova; Piotr Krutki. Prolonged activity evokes potentiation and the “sag” phenomenon in slow motor units of rat soleus. Acta Neurobiologiae Experimentalis 2016, 76, 152 -157.
AMA StyleHanna Drzymała-Celichowska, Rositsa Raikova, Piotr Krutki. Prolonged activity evokes potentiation and the “sag” phenomenon in slow motor units of rat soleus. Acta Neurobiologiae Experimentalis. 2016; 76 (2):152-157.
Chicago/Turabian StyleHanna Drzymała-Celichowska; Rositsa Raikova; Piotr Krutki. 2016. "Prolonged activity evokes potentiation and the “sag” phenomenon in slow motor units of rat soleus." Acta Neurobiologiae Experimentalis 76, no. 2: 152-157.
Introduction: The influence of long‐term muscle overload on force regulation and electrical properties of motor units (MUs) was investigated in rats. Methods: Compensatory overload of the medial gastrocnemius was induced by tenotomy of its synergists. Electrophysiological experiments were performed on functionally isolated MUs 3 months after the surgery. Results: Force‐frequency curves for overloaded MUs were shifted rightwards to control, thus MUs developed the same relative tetanic forces at higher frequencies. Higher force increase was achieved in response to an increase in stimulation frequency in overloaded fast MUs in comparison to control. The optimal tetanic contraction, characterized by the highest force‐time area per pulse, was evoked at higher stimulation frequencies for all overloaded MUs except FF. Only minor adaptive changes in MU action potentials occurred. Conclusions: Compensatory muscle overload leads to substantial modifications in MU force development mechanisms, which are MU type‐specific and influence whole muscle force regulation. This article is protected by copyright. All rights reserved.
Katarzyna Kryściak; Jan Celichowski; Hanna Drzymała-Celichowska; Phillip F. Gardiner; Piotr Krutki. Force regulation and electrical properties of motor units in overloaded muscle. Muscle & Nerve 2015, 53, 96 -106.
AMA StyleKatarzyna Kryściak, Jan Celichowski, Hanna Drzymała-Celichowska, Phillip F. Gardiner, Piotr Krutki. Force regulation and electrical properties of motor units in overloaded muscle. Muscle & Nerve. 2015; 53 (1):96-106.
Chicago/Turabian StyleKatarzyna Kryściak; Jan Celichowski; Hanna Drzymała-Celichowska; Phillip F. Gardiner; Piotr Krutki. 2015. "Force regulation and electrical properties of motor units in overloaded muscle." Muscle & Nerve 53, no. 1: 96-106.
Mathematical decomposition of tetanic contractions of slow motor units (MUs) of the rat heterogeneous medial gastrocnemius muscle revealed immense variability of twitch-shape responses to successive pulses, contrary to results obtained for fast MUs. The aim of this study in rat soleus muscle, almost exclusively composed of slow MUs, was to reveal whether such variability of twitch-shape decomposed components was a common property of slow MUs in the two studied muscles, and whether ranges of the force amplitude or time parameters of these decomposed twitches showed sex differences. Unfused tetanic contractions evoked by stimulation at variable interpulse intervals were analyzed for 10 MUs of males and 10 MUs of females. Significantly higher variability between parameters of the decomposed responses was observed for male soleus MUs, as the mean ratio of forces of the strongest decomposed twitch and the first (the weakest) decomposed twitch amounted to 3.8 for males and 2.8 for females. The ratios of the contraction times of the longest decomposed to the first twitch were much more similar between male and female MUs, 2.6 and 2.9, respectively. Consequently, the mean ratio of the force-time area for the strongest decomposed to the first twitch was much bigger in male than female MUs (7.35 vs. 5.07, respectively). Our observations indicate that high variability of responses to successive stimuli is a general property of slow MUs in different rat muscles, but the mechanisms of summation of individual twitches into tetanic contractions of MUs are not identical for male and female rats.
Hanna Drzymała-Celichowska; Rositsa Raikova; Piotr Krutki. Decomposition of motor unit tetanic contractions of rat soleus muscle: Differences between males and females. Journal of Biomechanics 2015, 48, 3097 -3102.
AMA StyleHanna Drzymała-Celichowska, Rositsa Raikova, Piotr Krutki. Decomposition of motor unit tetanic contractions of rat soleus muscle: Differences between males and females. Journal of Biomechanics. 2015; 48 (12):3097-3102.
Chicago/Turabian StyleHanna Drzymała-Celichowska; Rositsa Raikova; Piotr Krutki. 2015. "Decomposition of motor unit tetanic contractions of rat soleus muscle: Differences between males and females." Journal of Biomechanics 48, no. 12: 3097-3102.
More accurate muscle models require appropriate modelling of individual twitches of motor units (MUs) and their unfused tetanic contractions. It was shown in our previous papers, using a few MUs, that modelling of unfused tetanic force curves by summation of equal twitches is not accurate, especially for slow MUs. The aim of this study was to evaluate this inaccuracy using a statistical number of MUs of the rat medial gastrocnemius muscle (15 of slow, 15 of fast resistant and 15 of fast fatigable type). Tetanic contractions were evoked by trains of 41 stimuli at random interpulse intervals and different mean frequencies, resembling discharge patterns observed during natural muscle activity. The tetanic curves were calculated by the summation of equal twitches according to the respective experimental patterns. The previously described 6-parameter analytical function for twitch modelling was used. Comparisons between the experimental and the modelled curves were made using two coefficients: the fit coefficient and the area coefficient. The errors between modelled and experimental tetanic forces were substantially different between the three MU types. The error was the most significant for slow MUs, which develop much higher forces in real contractions than could be predicted based on the summation of equal twitches, while the smallest error was observed for FF MUs – their recorded tetanic forces were similar to those predicted by modelling. The obtained results indicate the importance of the inclusion of the type-specific non-linearity in the summation of successive twitch-like contractions of MUs in order to increase the reliability of modelling skeletal muscle force.
Rositsa Raikova; Hristo Aladjov; Piotr Krutki; Jan Celichowski. Estimation of the error between experimental tetanic force curves of MUs of rat medial gastrocnemius muscle and their models by summation of equal successive contractions. Computer Methods in Biomechanics and Biomedical Engineering 2015, 19, 763 -770.
AMA StyleRositsa Raikova, Hristo Aladjov, Piotr Krutki, Jan Celichowski. Estimation of the error between experimental tetanic force curves of MUs of rat medial gastrocnemius muscle and their models by summation of equal successive contractions. Computer Methods in Biomechanics and Biomedical Engineering. 2015; 19 (7):763-770.
Chicago/Turabian StyleRositsa Raikova; Hristo Aladjov; Piotr Krutki; Jan Celichowski. 2015. "Estimation of the error between experimental tetanic force curves of MUs of rat medial gastrocnemius muscle and their models by summation of equal successive contractions." Computer Methods in Biomechanics and Biomedical Engineering 19, no. 7: 763-770.