In the conventional view a muscle is composed of intermediate structures before its further division into microscopic muscle fibers.Our experiments in mice have confirmed this intermediate structure is composed of the...In the conventional view a muscle is composed of intermediate structures before its further division into microscopic muscle fibers.Our experiments in mice have confirmed this intermediate structure is composed of the lamella cluster formed by motor endplates,the innervating nerve branches and the corresponding muscle fibers,which can be viewed as an independent structural and functional unit.In this study,we verified the presence of these muscle construction units in rabbits.The results showed that the muscular branch of the femoral nerve sent out 4–6 nerve branches into the quadriceps and the tibial nerve sent out 4–7 nerve branches into the gastrocnemius.When each nerve branch of the femoral nerve was stimulated from the most lateral to the medial,the contraction of the lateral muscle,intermediate muscle and medial muscle of the quadriceps could be induced by electrically stimulating at least one nerve branch.When stimulating each nerve branch of the tibial nerve from the lateral to the medial,the muscle contraction of the lateral muscle 1,lateral muscle 2,lateral muscle 3 and medial muscle of the gastrocnemius could be induced by electrically stimulating at least one nerve branch.Electrical stimulation of each nerve branch resulted in different electromyographical waves recorded in different muscle subgroups.Hematoxylin-eosin staining showed most of the nerve branches around the neuromuscular junctions consisted of one individual neural tract,a few consisted of two or more neural tracts.The muscles of the lower limb in the rabbit can be subdivided into different muscle subgroups,each innervated by different nerve branches,thereby allowing much more complex muscle activities than traditionally stated.Together,the nerve branches and the innervated muscle subgroups can be viewed as an independent structural and functional unit.This study was approved by the Animal Ethics Committee of Peking University People’s Hospital(approval No.2019 PHE027)on October 20,2019.展开更多
The forced lengthening of an activated skeletal muscle has been termed an eccentric contraction(EC).This review highlights the mechanically unique nature of the EC and focuses on the specific disruption of proteins wi...The forced lengthening of an activated skeletal muscle has been termed an eccentric contraction(EC).This review highlights the mechanically unique nature of the EC and focuses on the specific disruption of proteins within the cell known as cytoskeletal proteins.The major intermediate filament cytoskeletal protein,desmin,has been the focus of work in this area because changes to desmin occur within minutes of ECs and because desmin has been shown to play both a mechanical and biologic role in a muscle's response to EC.It is hoped that these types of studies will assist in decreasing the incidence of muscle injury in athletes and facilitating the development of new therapies to treat muscle injuries.展开更多
Neuromuscular activity is suppressed during maximal eccentric(ECC)muscle contraction in untrained subjects owing to attenuated levels of central activation and reduced spinal motor neuron(MN)excitability indicated by ...Neuromuscular activity is suppressed during maximal eccentric(ECC)muscle contraction in untrained subjects owing to attenuated levels of central activation and reduced spinal motor neuron(MN)excitability indicated by reduced electromyography signal amplitude,diminished evoked H-reflex responses,increased autogenic MN inhibition,and decreased excitability in descending corticospinal motor pathways.Maximum ECC muscle force recorded during maximal voluntary contraction can be increased by superimposed electrical muscle stimulation only in untrained individuals and not in trained strength athletes,indicating that the suppression in MN activation is modifiable by resistance training.In support of this notion,maximum ECC muscle strength can be increased by use of heavy-load resistance training owing to a removed or diminished suppression in neuromuscular activity.Prolonged(weeks to months)of heavy-load resistance training results in increased H-reflex and V-wave responses during maximal ECC muscle actions along with marked gains in maximal ECC muscle strength,indicating increased excitability of spinal MNs,decreased presynaptic and/or postsynaptic MN inhibition,and elevated descending motor drive.Notably,the use of supramaximal ECC resistance training can lead to selectively elevated V-wave responses during maximal ECC contraction,demonstrating that adaptive changes in spinal circuitry function and/or gains in descending motor drive can be achieved during maximal ECC contraction in response to heavy-load resistance training.展开更多
We employ a mechanical model of sarcomere to quantitatively investigate how adenosine triphosphate (ATP) concentration affects motor force regulation during skeletal muscle contraction. Our simulation indicates that t...We employ a mechanical model of sarcomere to quantitatively investigate how adenosine triphosphate (ATP) concentration affects motor force regulation during skeletal muscle contraction. Our simulation indicates that there can be negative cross-bridges resisting contraction within the sarcomere and higher ATP concentration would decrease the resistance force from negative cross-bridges by promoting their timely detachment. It is revealed that the motor force is well regulated only when ATP concentration is above a certain level. These predictions may provide insights into the role of ATP in regulating coordination among multiple motors.展开更多
In this work, mechanisms of influence of protein sensibility of an organism on contractile function of the isolated skeletal muscles of the mouse—“fast”—musculus extensor digitorum longus, “mixed”—musculus diap...In this work, mechanisms of influence of protein sensibility of an organism on contractile function of the isolated skeletal muscles of the mouse—“fast”—musculus extensor digitorum longus, “mixed”—musculus diaphragma and “slow”— musculus soleus are investigated. It is shown that at a protein sensitization all “fast”, “mixed” and “slow” skeletal muscles change the contractile properties. The vector of these changes for muscles with a various phenotypes carries opposite character. Force of the reduction caused carbacholine at a “slow” and “mixed” muscles increase, at “fast”—decreases. A vector of change of force of reduction on carbacholine at protein sensitization at these skeletal muscles correlates with changes of non-quantum secretion acetylcholine in a zone of a trailer plate. Opposite changes of functional properties of “fast” and “mixed” muscles and “slow” muscles of a shin of the mouse at protein sensitization are caused by dynamics cholinoceptive processes of excitation of membrane muscular fibers. It comes out with the assumption, that change of the contraction functions of skeletal muscles at protein sensitization is caused by changes of cholinoceptive processes of excitation of a membrane of muscular fibers, and other changes in system of electro-mechanical interface.展开更多
Previous research has shown that smooth muscle of the stomach undergoes developmental changes in the intracellular regulatory mechanism responsible for the contractile process. Whether these developmental changes rela...Previous research has shown that smooth muscle of the stomach undergoes developmental changes in the intracellular regulatory mechanism responsible for the contractile process. Whether these developmental changes relate to differences in the expression and/or activity of the key enzymes regulating smooth muscle contraction has not been previously evaluated. Therefore, we aimed to examine the expression and activation of the small monomeric G protein "Rho A" and Rho kinase(ROCK) as well as their correlation with the contraction of gastric smooth muscle cells(GSMCs) in newborn vs. adult rats. Freshly isolated single GSMCs from Sprague-Dawley rats at 1 week(newborn) and 3 months(adult) of age were used in the study. Protein and m RNA expression levels of both ROCK2 and total Rho A were higher in adult compared to newborn rats. Moreover, acetylcholine(ACh)-induced contractions of GSMCs in adult rats were significantly higher than that in newborn animals. Meanwhile,ROCK and Rho activation was higher in adult stomach cells compared to newborn ones. Pretreatment of GSMCs with Y-27632, the ROCK inhibitor, significantly reduced ACh-induced contraction in both groups of cells and greatly abolished contractile differences. In conclusion, our results indicate that Rho A/ROCK pathway and contraction of stomach muscle cells are under developmental regulation.展开更多
In order to detect and assess the muscle fatigue state with the surface electromyography(sEMG) characteristic parameters,this paper carried out a series of isometric contraction experiments to induce the fatigue on th...In order to detect and assess the muscle fatigue state with the surface electromyography(sEMG) characteristic parameters,this paper carried out a series of isometric contraction experiments to induce the fatigue on the forearm muscles from four subjects,and recorded the sEMG signals of the flexor carpi ulnaris.sEMG's median frequency(MDF) and mean frequency(MF) were extracted by short term Fourier transform(STFT),and the root mean square(RMS) of wavelet coefficients in the frequency band of 5—45 Hz was obtained by continuous wavelet transform(CWT).The results demonstrate that both MDF and MF show downward trends within 1 min; however,RMS shows an upward trend within the same time.The three parameters are closely correlated with absolute values of mean correlation coefficients greater than 0.8.It is suggested that the three parameters above can be used as reliable indicators to evaluate the level of muscle fatigue during isometric contractions.展开更多
AIM: To investigate the effects of areca on the contractile activity of isolated colonic muscle strips in rats and mechanism involved. METHODS: Each strip (LMPC, longitudinal muscle of proximal colon; CMPC, circular m...AIM: To investigate the effects of areca on the contractile activity of isolated colonic muscle strips in rats and mechanism involved. METHODS: Each strip (LMPC, longitudinal muscle of proximal colon; CMPC, circular muscle of proximal colon; LMDC, longitudinal muscle of distal colon; CMDC, circular muscle of distal colon.) was suspended in a tissue chamber containing 5 mL Krebs solution (37 degrees C), bubbled continuously with 950 mL.L(-1) O(2) and 50 mL.L(-1) CO(2). The mean contractile amplitude (A), the resting tension (T), and the contractile frequency (F) were simultaneously recorded on recorders. RESULTS: Areca dose dependently increased the mean contractile amplitude, the resting tension of proximal and distal colonic smooth muscle strips in rats (P【0.05). It also partly increased the contractile frequency of colonic smooth muscle strips in rats (P【0.05). The effects were partly inhibited by atropine (the resting tension of LMPC decreased from 0.44 +/- 0.12 to 0.17 +/- 0.03; the resting tension of LMDC decreased from 0.71 +/- 0.14 to 0.03 +/- 0.01; the mean contractile amplitude of LMPC increased from -45.8 +/- 7.2 to -30.5 +/- 2.9; the motility index of CMDC decreased from 86.6 +/- 17.3 to 32.8 +/- 9.3; P【0.05 vs areca), but the effects were not inhibited by hexamethonium (P】0.05). CONCLUSION: Areca stimulated the motility of isolated colonic smooth muscle strips in rats. The stimulation of areca might be relevant with M receptor partly.展开更多
This study is aimed at assessing muscle fatigue during a static contraction using multifractal analysis and found that the surface electromyographic （SEMG） signals characterized multiffactality during a static contr...This study is aimed at assessing muscle fatigue during a static contraction using multifractal analysis and found that the surface electromyographic （SEMG） signals characterized multiffactality during a static contraction. By applying the method of direct determination ofthef（a） singularity spectrum, the area of the multifractal spectrum of the SEMG signals was computed. The results showed that the spectrum area significantly increased during muscle fatigue. Therefore the area could be used as an assessor of muscle fatigue. Compared with the median frequency （MDF）--the most popular indicator of muscle fatigue, the spectrum area presented here showed higher sensitivity during a static contraction. So the singularity spectrum area is considered to be a more effective indicator than the MDF for estimating muscle fatigue.展开更多
The spontaneous oscillatory contraction（SPOC） of myofibrils is the essential property inherent to the contractile system of muscle. Muscle contraction results from cyclic interactions between actin filament and myos...The spontaneous oscillatory contraction（SPOC） of myofibrils is the essential property inherent to the contractile system of muscle. Muscle contraction results from cyclic interactions between actin filament and myosin II which is a dimeric motor protein with two heads. Taking the two heads of myosin II as an indivisible element and considering the effects of cooperative behavior between the two heads on rate constants in the mechanochemical cycle, the present work proposes the tenstate mechanochemical cycle model for myosin II dimer. The simulations of this model show that the proportion of myosin II in different states periodically changes with time, which results in the sustained oscillations of contractive tension, and serves as the primary factor for SPOC. The good fit of this model to experimental results suggests that the cooperative interaction between the two heads of myosin II dimer may be one of the underlying mechanisms for muscle contraction.展开更多
AIM： To study the direct correlation between gastric dysrhythrnias and in vivo gastric muscle tone. METHODS： Five healthy dogs were implanted with 4 pairs of electrodes along the greater curvature, with a strain gau...AIM： To study the direct correlation between gastric dysrhythrnias and in vivo gastric muscle tone. METHODS： Five healthy dogs were implanted with 4 pairs of electrodes along the greater curvature, with a strain gauge （SG） being sutured parallel to the distal electrodes （2 cm above the pylorus）. Intravenous vasopressin was given to induce gastric dysrhythrnia. The percentage of regular slow waves and SG energy were calculated. RESULTS： （1） the regularity of gastric rnyoelectric activity （GMA） was reduced during and after infusion of vasopressin; （2） SG energy was significantly decreased during the infusion of vasopressin; （3） the decrease in SG energy was well correlated with the reduction in GMA regularity; （4） SG energy was negatively correlated with bradygastria and tachygastria. CONCLUSION： Vasopressin inhibits gastric contractions and impairs gastric slow waves; gastric dysrhythrnias are associated with the reduced antral muscle contractions, and are indicative of antral hypornotility.展开更多
AIM:To investigate the pathway(s)mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent,bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction...AIM:To investigate the pathway(s)mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent,bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction. METHODS:Circular smooth muscle strips from the antrum of Sprague-Dawley rats were mounted in muscle baths in Krebs buffer.Isometric tension was recorded.Cumulative concentration-response curves were obtained for(+)-cis- dioxolane(cD),a nonspecific muscarinic agonist,at 10^(-8)- 10^(-4)mol/L,in the presence of tetrodotoxin(TTX,10^(-7)mol/L). Results were normalized to cross sectional area.A repeat concentration-response curve was obtained after incubation of the muscle for 90 min with antagonists for M1(pirenzepine), M2(methoctramine)and M3(darifenadn)muscarinic receptor subtypes.The sensitivity to PTX was tested by the ip injection of 100 mg/kg of PTX 5 d before the experiment.The antral circular smooth muscles were removed from PTX-treated and non-treated rats as strips and dispersed smooth muscle cells to identify whether PTX-linked pathway mediated the contractility to bethanechol. RESULTS:A dose-dependent contractile response observed with bethanechol,was not affected by TTx.The pretreatment of rats with pertussis toxin decreased the contraction induced by bethanechol.Lack of calcium as well as the presence of the L-type calcium channel blocker,nifedipine,also inhibited the cholinergic contraction,with a reduction in response from 2.5±0.4 g/mm^2 to 1.2±0.4 g/mm^2(P<0.05).The dose- response curves were shifted to the right by muscarinic antagonists in the following order of affinity:darifenacin (M_3)>methocramine(M_2)>pirenzepine(M_1). CONCLUSION:The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pathway(s)involving pertussis-toxin sensitive GTP-binding proteins and to extracellular calcium via L-type voltage gated calcium channels.The presence of the residual contractile response after the treatment with nifedipine,suggests that an additional pathway could mediate the cholinergic contraction.The involvement of more than one muscarinic receptor(functionally predominant type 3 over type 2)also suggests more than one pathway mediating the cholinergic contraction in rat antrum.展开更多
AIM: To investigate the effect and the possible mechanism of ginsenoside Rb1 on small intestinal smooth muscle motility in mice. METHODS: Intestinal smooth muscle strips were isolated from male ICR mice (5 wk old), an...AIM: To investigate the effect and the possible mechanism of ginsenoside Rb1 on small intestinal smooth muscle motility in mice. METHODS: Intestinal smooth muscle strips were isolated from male ICR mice (5 wk old), and the effect of ginsenoside Rb1 on spontaneous contraction was recorded with an electrophysiolograph. The effect of ginsenoside Rb1 on ion channel currents, including the voltage-gated K + channel current (IK V ), calcium-activated potassium channel currents (IK Ca ), spontaneous transient outward currents and ATP-sensitive potassium channel current (IK ATP ), was recorded on freshly isolated single cells using the whole-cell patch clamp technique. RESULTS: Ginsenoside Rb1 dose-dependently inhibited the spontaneous contraction of intestinal smooth muscle by 21.15% ± 3.31%, 42.03% ± 8.23% and 67.23% ± 5.63% at concentrations of 25 μmol/L, 50 μmol/L and 100 μmol/L, respectively (n=5,P<0.05). The inhibitory effect of ginsenoside Rb1 on spontaneous contraction was significantly but incompletely blocked by 10 mmol/L tetraethylammonium or 0.5 mmol/L 4-aminopyridine, respectively (n=5, P<0.05). However, the inhibitory effect of ginsenoside Rb1 on spontaneous contraction was not affected by 10 μmol/L glibenclamide or 0.4 μmol/L tetrodotoxin. At the cell level, ginsenoside Rb1 increased outward potassium currents, and IK V was enhanced from 1137.71 ± 171.62 pA to 1449.73 ± 162.39 pA by 50 μmol/L Rb1 at +60 mV (n=6, P<0.05). Ginsenoside Rb1 increased IK Ca and enhanced the amplitudes of spontaneous transient outward currents from 582.77 ± 179.09 mV to 788.12 ± 278.34 mV (n=5, P<0.05). However, ginsenoside Rb1 (50 μmol/L) had no significant effect on IK ATP (n=3, P<0.05). CONCLUSION: These results suggest that ginsenoside Rb1 has an inhibitory effect on the spontaneous contraction of mouse intestinal smooth muscle mediated by the activation of IK V and IK Ca , but the K ATP channel was not involved in this effect.展开更多
BACKGROUND In the first studies of electrochemotherapy(ECT),small cutaneous metastases were treated and only mild or moderate pain was observed;therefore,pain was not considered a significant issue.As the procedure be...BACKGROUND In the first studies of electrochemotherapy(ECT),small cutaneous metastases were treated and only mild or moderate pain was observed;therefore,pain was not considered a significant issue.As the procedure began to be applied to larger cutaneous metastases,pain was reported more frequently.For that reason,reduction of both muscle contractions and pain have been investigated over the years.AIM To present an overview of different protocols described in literature that aim to reduce muscle contractions and pain caused by the electroporation(EP)effect in both ECT and irreversible EP treatments.METHODS Thirty-three studies published between January 1999 and November 2020 were included.Different protocol designs and electrode geometries that reduce patient pain and the number of muscle contractions and their intensity were analysed.RESULTS The analysis showed that both high frequency and bipolar/biphasic pulses can be used to reduce pain and muscle contractions in patients who undergo EP treatments.Moreover,adequate electrode design can decrease EP-related morbidity.Particularly,needle length,diameter and configuration of the distance between the needles can be optimised so that the muscle volume crossed by the current is reduced as much as possible.Bipolar/biphasic pulses with an inadequate pulse length seem to have a less evident effect on the membrane permeability compared with the standard pulse protocol.For that reason,the number of pulses and the voltage amplitude,as well as the pulse duration and frequency,must be chosen so that the dose of delivered energy guarantees EP efficacy.CONCLUSION Pain reduction in EP-based treatments can be achieved by appropriately defining the protocol parameters and electrode design.Most results can be achieved with high frequency and/or bipolar/biphasic pulses.However,the efficacy of these alternative protocols remains a crucial point to be assessed further.展开更多
Muscle unloading due to long-term exposure of weightlessness or simulated weightlessness causes atrophy, loss of functional capacity, impaired locomotor coordination, and decreased resistance to fatigue in the antigra...Muscle unloading due to long-term exposure of weightlessness or simulated weightlessness causes atrophy, loss of functional capacity, impaired locomotor coordination, and decreased resistance to fatigue in the antigravity muscles of the lower limbs. Besides reducing astronauts' mobility in space and on returning to a gravity environment, the molecular mechanisms for the adaptation of skeletal muscle to unloading also play an important medical role in conditions such as disuse and paralysis. The tail-suspended rat model was used to simulate the effects of weightlessness on skeletal muscles and to induce muscle unloading in the rat hindlimb. Our series studies have shown that the maximum of twitch tension and the twitch duration decreased significantly in the atrophic soleus muscles, the maximal tension of high-frequency tetanic contraction was significantly reduced in 2-week unloaded soleus muscles, however, the fatigability of highfrequency tetanic contraction increased after one week of unloading. The maximal isometric tension of intermittent tetanic contraction at optimal stimulating frequency did not alter in 1-and 2-week unloaded soleus, but significantly decreased in 4-week unloaded soleus. The 1-week unloaded soleus, but not extensor digitorum longus(EDL), was more susceptible to fatigue during intermittent tetanic contraction than the synchronous controls. The changes in K+ channel characteristics may increase the fatigability during high-frequency tetanic contraction in atrophic soleus muscles. High fatigability of intermittent tetanic contraction may be involved in enhanced activity of sarcoplasmic reticulum Ca2+-ATPase(SERCA) and switching from slow to fast isoform of myosin heavy chain, tropomyosin, troponin I and T subunit in atrophic soleus muscles. Unloaded soleus muscle also showed a decreased protein level of neuronal nitric oxide synthase(nNOS), and the reduction in nNOS-derived NO increased frequency of calcium sparks and elevated intracellular resting Ca2+ concentration([Ca2+]i) in unloaded soleus muscles. High [Ca2+]i activated calpain-1 which induced a higher degradation of desmin. Desmin degradation may loose connections between adjacent myofibrils and further misaligned Z-disc during repeated tetanic contractions. Passive stretch in unloaded muscle could preserve the stability of sarcoplasmic reticulum Ca2+ release channels by means of keeping nNOS activity, and decrease the enhanced protein level and activity of calpain to control levels in unloaded soleus muscles. Therefore, passive stretch restored normal appearance of Z-disc and resisted in part atrophy of unloaded soleus muscles. The above results indicate that enhanced fatigability of high-frequency tetanic contraction is associated to the alteration in K+ channel characteristics, and elevated SERCA activity and slow to fast transition of myosin heavy chain(MHC) isoforms increases fatigability of intermittent tetanic contraction in atrophic soleus muscle. The sarcomeric damage induced by tetanic contraction can be retarded by stretch in atrophic soleus muscles.展开更多
Given recent technological developments, ultrasound Doppler can provide valuable measurements of blood velocity/flow in the conduit artery with high temporal resolution. In human-applied science such as exercise physi...Given recent technological developments, ultrasound Doppler can provide valuable measurements of blood velocity/flow in the conduit artery with high temporal resolution. In human-applied science such as exercise physiology, hemodynamic measurements in the conduit artery is commonly performed by blood flow feeding the exercising muscle, as the increase in oxygen uptake (calculated as a product of arterial blood flow to the exercising limb and the arterio-venous oxygen difference) is directly proportional to the work performed. The increased oxygen demand with physical activity is met through a central mechanism, an increase in cardiac output and blood pressure, as well as a peripheral mechanism, an increase in vascular conductance and oxygen extraction (a major part of the whole exercising muscles) from the blood. The increase in exercising muscle blood flow in relation to the target workload (quantitative response) may be one indicator in circulatory adjustment for the ac- tivity of muscle metabolism. Therefore, the determination of local blood flow dynamics (potential oxygen supply) feeding repeated (rhythmic) muscle contractions can contribute to the understanding of the factors limiting work capacity including, for instance, muscle metabolism, substance utilization and magnitude of vasodilatation in the exercising muscle. Using non-invasive measures of pulsed Doppler ultrasound, the validity of blood velocity/flow in the forearm or lower limb conduit artery feeding to the muscle has been previously demonstrated during rhythmic muscle exercise. For the evaluation of exercising blood flow, not only muscle contraction induced internal physiological variability, or fluctuations in the magnitude of blood velocity due to spontaneous muscle contraction and relaxation induced changes in force curve intensity, superimposed in cardiac beat-by-beat, but also the alterations in the blood velocity (external variability) due to a temporary sudden change in the achieved workload, compared to the target workload, should be considered. Furthermore, a small amount of inconsistency in the voluntary muscle contraction force at each kick seems to be unavoidable, and may influence exercising muscle blood flow, although subjects attempt to perform precisely similar repeated voluntary muscle contractions at target workload (muscle contraction force). This review presents the methodological considerations for the variability of exercising blood velocity/flow in the limb conduit artery during dynamic leg exercise assessed by pulsed Doppler ultrasound in relation to data previously reported in original research.展开更多
We aimed to investigate the association between mobility and skeletal muscle strength by using magnetic resonance diffusion tensor imaging (DTI). This study included 20 healthy male volunteers (mean age, 21.8 ± 1...We aimed to investigate the association between mobility and skeletal muscle strength by using magnetic resonance diffusion tensor imaging (DTI). This study included 20 healthy male volunteers (mean age, 21.8 ± 1.1 years). The maximum voluntary strength (MVC) of each participant was measured with the ankle joint in plantar and dorsal flexion using an instrument for measuring muscle strength. Moreover, magnetic resonance imaging (MRI) was performed with the ankle joint at rest, in plantar flexion, and in dorsal flexion. For imaging, a 1.5-T MRI device was used, and a diffusion-weighted stimulated echo-planar imaging pulse sequence. Tensor eigenvalues (λ), fractional anisotropy (FA), and the apparent diffusion coefficient (ADC) were calculated from data obtained by DTI. The resulting MRI data were compared to the data on muscle mobility or strength and statistically analyzed. Regarding changes in DTI indices during muscle movements, anisotropy of the tibialis anterior was significantly increased from rest to plantar flexion (P < 0.01), whereas no significant change was observed in dorsal flexion (n.s.). In contrast, the extent of significant changes in anisotropy of the medial gastrocnemius (mGC) and soleus (SOL) was small at plantar flexion (mGC, P < 0.01;SOL, n.s.), whereas the indices were significantly increased at dorsal flexion (P < 0.01). Regarding the correlation between MVC of each skeletal muscle and the DTI indices, FA and λ3 were significantly correlated in movements involving the muscles, whereas no significant correlation was observed in movements not involving them. Changes in intramuscular water molecules by elongation and contraction of the skeletal muscle fibers could be assumed to affect changes in diffusional anisotropy. When muscles contract, the space between myocytes was reduced and they might become increasingly dense. Moreover, diffusional anisotropy increased with increasing MVC, whereas ADC remained unchanged. DTI was suggested to produce measurements similar to the degree of muscle strength.展开更多
We developed an eccentric contraction induced electrical stimulation (ES) training system. The purpose of this study was to investigate whether the eccentric contraction induced ES enhance the knee extension torque co...We developed an eccentric contraction induced electrical stimulation (ES) training system. The purpose of this study was to investigate whether the eccentric contraction induced ES enhance the knee extension torque compared with typical ES. Twenty-two young untrained men (age: 23 ± 3 years) in the acute response trial (single training) and seven untrained men in the long period training trial (for 6 weeks) were studied. We measured muscle thickness and knee extension torque evoked by ES with eccentric contraction training system (ES + ECC) or ES alone for the quadriceps muscle of men. The levels of pain and discomfort were evaluated using numeric rating scale (NRS) and heart rate variability. The knee extension torque of ES + ECC was higher than that of ES alone in the acute response trial. There were no significant differences in the levels of pain and discomfort between ES and ES + ECC. Additionally, ES + ECC training for 6 weeks was effective on the quadriceps muscle thickness and knee extension torque. In contrast, the ES alone training failed to increase muscle thickness and knee extension torque. These results suggest that eccentric contraction induced ES would have the potential to become an effective intervention to promote muscle strengthening.展开更多
AIM:To study the pharmacological profile and inhibition of smooth muscle contraction by YFa and its analogs in conjunction with their receptor selectivity. METHODS:The effects of YFa and its analogs (D-Ala2) YFa, Y (D...AIM:To study the pharmacological profile and inhibition of smooth muscle contraction by YFa and its analogs in conjunction with their receptor selectivity. METHODS:The effects of YFa and its analogs (D-Ala2) YFa, Y (D-Ala2) GFMKKKFMRF amide and Des-Phe-YGGFMKKKFMR amide in guinea pig ileum (GPI) and mouse vas deferens (MVD) motility were studied using an isolated tissue organ bath system, and morphine and DynA (1-13) served as controls. Acetylcholine was used for muscle stimulation. The observations were validated by specific antagonist pretreatment experiments using naloxonazine, naltrindole and norbinaltor-phimine norBNI. RESULTS:YFa did not demonstrate significant inhibition of GPI muscle contraction as compared with mor-phine (15% vs 62%, P = 0.0002), but moderate inhibition of MVD muscle contraction, indicating the role of κ opioid receptors in the contraction. A moderate inhibition of GPI muscles by (Des-Phe) YFa revealed the role of anti-opiate receptors in the smooth muscle contraction. (D-Ala-2) YFa showed significant inhibition of smooth muscle contraction, indicating the involvement of mainly δ receptors in MVD contraction. These results were supported by specific antagonist pretreatment assays. CONCLUSION:YFa revealed its side-effect-free analgesic properties with regard to arrest of gastroin-testinal transit. The study provides evidences for the involvement of κ and anti-opioid receptors in smooth muscle contraction.展开更多
The aim of this study was to determine the within-day and between-days reliability of surface electromyographic (EMG) power spectral analysis in assessing fatigability of the vastus medialis (VM) muscle during knee an...The aim of this study was to determine the within-day and between-days reliability of surface electromyographic (EMG) power spectral analysis in assessing fatigability of the vastus medialis (VM) muscle during knee and hip flexion under constant load application. The subjects were 13 healthy adult men free of knee abnormalities. Surface EMG was recorded from vastus medialis obliquus (VMO) and vastus medialis longus (VML) during sustained isometric contractions at 60% of maximal voluntary contraction until exhaustion on the leg press machine (static leg press test). Linear regression analysis was applied to median frequency (MF) time series to calculate initial MF and MF slope. For VMO and VML, the initial MF showed moderate to high reliability, while the MF slope showed high reliability (Intraclass correlation coefficient (ICC) = initial MF: 0.63 - 0.92, MF slope: 0.70 - 0.86). The results demonstrated that spectral analysis of surface EMG recording during isometric VM muscle contraction has high within-day and between-days reliability in the assessment of fatigability of the VMO and VML.展开更多
基金supported by Peking University Clinical Scientist Program of China,No.BMU2019LCKXJ005the Fundamental Research Funds for the Central Universities,Key Laboratory of Trauma and Neural Regeneration,Ministry of Education of China,No.BMU2019XY007-01(both to BGJ)。
文摘In the conventional view a muscle is composed of intermediate structures before its further division into microscopic muscle fibers.Our experiments in mice have confirmed this intermediate structure is composed of the lamella cluster formed by motor endplates,the innervating nerve branches and the corresponding muscle fibers,which can be viewed as an independent structural and functional unit.In this study,we verified the presence of these muscle construction units in rabbits.The results showed that the muscular branch of the femoral nerve sent out 4–6 nerve branches into the quadriceps and the tibial nerve sent out 4–7 nerve branches into the gastrocnemius.When each nerve branch of the femoral nerve was stimulated from the most lateral to the medial,the contraction of the lateral muscle,intermediate muscle and medial muscle of the quadriceps could be induced by electrically stimulating at least one nerve branch.When stimulating each nerve branch of the tibial nerve from the lateral to the medial,the muscle contraction of the lateral muscle 1,lateral muscle 2,lateral muscle 3 and medial muscle of the gastrocnemius could be induced by electrically stimulating at least one nerve branch.Electrical stimulation of each nerve branch resulted in different electromyographical waves recorded in different muscle subgroups.Hematoxylin-eosin staining showed most of the nerve branches around the neuromuscular junctions consisted of one individual neural tract,a few consisted of two or more neural tracts.The muscles of the lower limb in the rabbit can be subdivided into different muscle subgroups,each innervated by different nerve branches,thereby allowing much more complex muscle activities than traditionally stated.Together,the nerve branches and the innervated muscle subgroups can be viewed as an independent structural and functional unit.This study was approved by the Animal Ethics Committee of Peking University People’s Hospital(approval No.2019 PHE027)on October 20,2019.
文摘The forced lengthening of an activated skeletal muscle has been termed an eccentric contraction(EC).This review highlights the mechanically unique nature of the EC and focuses on the specific disruption of proteins within the cell known as cytoskeletal proteins.The major intermediate filament cytoskeletal protein,desmin,has been the focus of work in this area because changes to desmin occur within minutes of ECs and because desmin has been shown to play both a mechanical and biologic role in a muscle's response to EC.It is hoped that these types of studies will assist in decreasing the incidence of muscle injury in athletes and facilitating the development of new therapies to treat muscle injuries.
文摘Neuromuscular activity is suppressed during maximal eccentric(ECC)muscle contraction in untrained subjects owing to attenuated levels of central activation and reduced spinal motor neuron(MN)excitability indicated by reduced electromyography signal amplitude,diminished evoked H-reflex responses,increased autogenic MN inhibition,and decreased excitability in descending corticospinal motor pathways.Maximum ECC muscle force recorded during maximal voluntary contraction can be increased by superimposed electrical muscle stimulation only in untrained individuals and not in trained strength athletes,indicating that the suppression in MN activation is modifiable by resistance training.In support of this notion,maximum ECC muscle strength can be increased by use of heavy-load resistance training owing to a removed or diminished suppression in neuromuscular activity.Prolonged(weeks to months)of heavy-load resistance training results in increased H-reflex and V-wave responses during maximal ECC muscle actions along with marked gains in maximal ECC muscle strength,indicating increased excitability of spinal MNs,decreased presynaptic and/or postsynaptic MN inhibition,and elevated descending motor drive.Notably,the use of supramaximal ECC resistance training can lead to selectively elevated V-wave responses during maximal ECC contraction,demonstrating that adaptive changes in spinal circuitry function and/or gains in descending motor drive can be achieved during maximal ECC contraction in response to heavy-load resistance training.
基金supported by the National Natural Science Foundation of China (Grants 11372279, 11572285)
文摘We employ a mechanical model of sarcomere to quantitatively investigate how adenosine triphosphate (ATP) concentration affects motor force regulation during skeletal muscle contraction. Our simulation indicates that there can be negative cross-bridges resisting contraction within the sarcomere and higher ATP concentration would decrease the resistance force from negative cross-bridges by promoting their timely detachment. It is revealed that the motor force is well regulated only when ATP concentration is above a certain level. These predictions may provide insights into the role of ATP in regulating coordination among multiple motors.
文摘In this work, mechanisms of influence of protein sensibility of an organism on contractile function of the isolated skeletal muscles of the mouse—“fast”—musculus extensor digitorum longus, “mixed”—musculus diaphragma and “slow”— musculus soleus are investigated. It is shown that at a protein sensitization all “fast”, “mixed” and “slow” skeletal muscles change the contractile properties. The vector of these changes for muscles with a various phenotypes carries opposite character. Force of the reduction caused carbacholine at a “slow” and “mixed” muscles increase, at “fast”—decreases. A vector of change of force of reduction on carbacholine at protein sensitization at these skeletal muscles correlates with changes of non-quantum secretion acetylcholine in a zone of a trailer plate. Opposite changes of functional properties of “fast” and “mixed” muscles and “slow” muscles of a shin of the mouse at protein sensitization are caused by dynamics cholinoceptive processes of excitation of membrane muscular fibers. It comes out with the assumption, that change of the contraction functions of skeletal muscles at protein sensitization is caused by changes of cholinoceptive processes of excitation of a membrane of muscular fibers, and other changes in system of electro-mechanical interface.
基金supported by Jordan University of Science&Technology,Irbid,Jordan(Grant No.20180087)
文摘Previous research has shown that smooth muscle of the stomach undergoes developmental changes in the intracellular regulatory mechanism responsible for the contractile process. Whether these developmental changes relate to differences in the expression and/or activity of the key enzymes regulating smooth muscle contraction has not been previously evaluated. Therefore, we aimed to examine the expression and activation of the small monomeric G protein "Rho A" and Rho kinase(ROCK) as well as their correlation with the contraction of gastric smooth muscle cells(GSMCs) in newborn vs. adult rats. Freshly isolated single GSMCs from Sprague-Dawley rats at 1 week(newborn) and 3 months(adult) of age were used in the study. Protein and m RNA expression levels of both ROCK2 and total Rho A were higher in adult compared to newborn rats. Moreover, acetylcholine(ACh)-induced contractions of GSMCs in adult rats were significantly higher than that in newborn animals. Meanwhile,ROCK and Rho activation was higher in adult stomach cells compared to newborn ones. Pretreatment of GSMCs with Y-27632, the ROCK inhibitor, significantly reduced ACh-induced contraction in both groups of cells and greatly abolished contractile differences. In conclusion, our results indicate that Rho A/ROCK pathway and contraction of stomach muscle cells are under developmental regulation.
基金Supported by the National Natural Science Foundation of China(No.81222021 and No.31011130042)the National Key Technology R&D Program of the Ministry of Science and Technology of China(No.2012BAI34B02)
文摘In order to detect and assess the muscle fatigue state with the surface electromyography(sEMG) characteristic parameters,this paper carried out a series of isometric contraction experiments to induce the fatigue on the forearm muscles from four subjects,and recorded the sEMG signals of the flexor carpi ulnaris.sEMG's median frequency(MDF) and mean frequency(MF) were extracted by short term Fourier transform(STFT),and the root mean square(RMS) of wavelet coefficients in the frequency band of 5—45 Hz was obtained by continuous wavelet transform(CWT).The results demonstrate that both MDF and MF show downward trends within 1 min; however,RMS shows an upward trend within the same time.The three parameters are closely correlated with absolute values of mean correlation coefficients greater than 0.8.It is suggested that the three parameters above can be used as reliable indicators to evaluate the level of muscle fatigue during isometric contractions.
基金the Natural Scientific Foundation of Shandong Province,No.Y2001C06
文摘AIM: To investigate the effects of areca on the contractile activity of isolated colonic muscle strips in rats and mechanism involved. METHODS: Each strip (LMPC, longitudinal muscle of proximal colon; CMPC, circular muscle of proximal colon; LMDC, longitudinal muscle of distal colon; CMDC, circular muscle of distal colon.) was suspended in a tissue chamber containing 5 mL Krebs solution (37 degrees C), bubbled continuously with 950 mL.L(-1) O(2) and 50 mL.L(-1) CO(2). The mean contractile amplitude (A), the resting tension (T), and the contractile frequency (F) were simultaneously recorded on recorders. RESULTS: Areca dose dependently increased the mean contractile amplitude, the resting tension of proximal and distal colonic smooth muscle strips in rats (P【0.05). It also partly increased the contractile frequency of colonic smooth muscle strips in rats (P【0.05). The effects were partly inhibited by atropine (the resting tension of LMPC decreased from 0.44 +/- 0.12 to 0.17 +/- 0.03; the resting tension of LMDC decreased from 0.71 +/- 0.14 to 0.03 +/- 0.01; the mean contractile amplitude of LMPC increased from -45.8 +/- 7.2 to -30.5 +/- 2.9; the motility index of CMDC decreased from 86.6 +/- 17.3 to 32.8 +/- 9.3; P【0.05 vs areca), but the effects were not inhibited by hexamethonium (P】0.05). CONCLUSION: Areca stimulated the motility of isolated colonic smooth muscle strips in rats. The stimulation of areca might be relevant with M receptor partly.
基金Project (No. 2005CB724303) supported by the National Basic Re-search Program (973) of China
文摘This study is aimed at assessing muscle fatigue during a static contraction using multifractal analysis and found that the surface electromyographic （SEMG） signals characterized multiffactality during a static contraction. By applying the method of direct determination ofthef（a） singularity spectrum, the area of the multifractal spectrum of the SEMG signals was computed. The results showed that the spectrum area significantly increased during muscle fatigue. Therefore the area could be used as an assessor of muscle fatigue. Compared with the median frequency （MDF）--the most popular indicator of muscle fatigue, the spectrum area presented here showed higher sensitivity during a static contraction. So the singularity spectrum area is considered to be a more effective indicator than the MDF for estimating muscle fatigue.
基金Project supported by Research Program of Science and Technology at Universities of Inner Mongolia Autonomous Region,China(Grant Nos.NJZY16493and NJZC17458)
文摘The spontaneous oscillatory contraction（SPOC） of myofibrils is the essential property inherent to the contractile system of muscle. Muscle contraction results from cyclic interactions between actin filament and myosin II which is a dimeric motor protein with two heads. Taking the two heads of myosin II as an indivisible element and considering the effects of cooperative behavior between the two heads on rate constants in the mechanochemical cycle, the present work proposes the tenstate mechanochemical cycle model for myosin II dimer. The simulations of this model show that the proportion of myosin II in different states periodically changes with time, which results in the sustained oscillations of contractive tension, and serves as the primary factor for SPOC. The good fit of this model to experimental results suggests that the cooperative interaction between the two heads of myosin II dimer may be one of the underlying mechanisms for muscle contraction.
文摘AIM： To study the direct correlation between gastric dysrhythrnias and in vivo gastric muscle tone. METHODS： Five healthy dogs were implanted with 4 pairs of electrodes along the greater curvature, with a strain gauge （SG） being sutured parallel to the distal electrodes （2 cm above the pylorus）. Intravenous vasopressin was given to induce gastric dysrhythrnia. The percentage of regular slow waves and SG energy were calculated. RESULTS： （1） the regularity of gastric rnyoelectric activity （GMA） was reduced during and after infusion of vasopressin; （2） SG energy was significantly decreased during the infusion of vasopressin; （3） the decrease in SG energy was well correlated with the reduction in GMA regularity; （4） SG energy was negatively correlated with bradygastria and tachygastria. CONCLUSION： Vasopressin inhibits gastric contractions and impairs gastric slow waves; gastric dysrhythrnias are associated with the reduced antral muscle contractions, and are indicative of antral hypornotility.
文摘AIM:To investigate the pathway(s)mediating rat antral circular smooth muscle contractile responses to the cholinomimetic agent,bethanechol and the subtypes of muscarinic receptors mediating the cholinergic contraction. METHODS:Circular smooth muscle strips from the antrum of Sprague-Dawley rats were mounted in muscle baths in Krebs buffer.Isometric tension was recorded.Cumulative concentration-response curves were obtained for(+)-cis- dioxolane(cD),a nonspecific muscarinic agonist,at 10^(-8)- 10^(-4)mol/L,in the presence of tetrodotoxin(TTX,10^(-7)mol/L). Results were normalized to cross sectional area.A repeat concentration-response curve was obtained after incubation of the muscle for 90 min with antagonists for M1(pirenzepine), M2(methoctramine)and M3(darifenadn)muscarinic receptor subtypes.The sensitivity to PTX was tested by the ip injection of 100 mg/kg of PTX 5 d before the experiment.The antral circular smooth muscles were removed from PTX-treated and non-treated rats as strips and dispersed smooth muscle cells to identify whether PTX-linked pathway mediated the contractility to bethanechol. RESULTS:A dose-dependent contractile response observed with bethanechol,was not affected by TTx.The pretreatment of rats with pertussis toxin decreased the contraction induced by bethanechol.Lack of calcium as well as the presence of the L-type calcium channel blocker,nifedipine,also inhibited the cholinergic contraction,with a reduction in response from 2.5±0.4 g/mm^2 to 1.2±0.4 g/mm^2(P<0.05).The dose- response curves were shifted to the right by muscarinic antagonists in the following order of affinity:darifenacin (M_3)>methocramine(M_2)>pirenzepine(M_1). CONCLUSION:The muscarinic receptors-dependent contraction of rat antral circular smooth muscles was linked to the signal transduction pathway(s)involving pertussis-toxin sensitive GTP-binding proteins and to extracellular calcium via L-type voltage gated calcium channels.The presence of the residual contractile response after the treatment with nifedipine,suggests that an additional pathway could mediate the cholinergic contraction.The involvement of more than one muscarinic receptor(functionally predominant type 3 over type 2)also suggests more than one pathway mediating the cholinergic contraction in rat antrum.
基金Supported by The National Natural Science Foundation of China, No. 30873328The State Administration of Traditional Chinese Medicine of the People’s Republic of China, No. 06-075930
文摘AIM: To investigate the effect and the possible mechanism of ginsenoside Rb1 on small intestinal smooth muscle motility in mice. METHODS: Intestinal smooth muscle strips were isolated from male ICR mice (5 wk old), and the effect of ginsenoside Rb1 on spontaneous contraction was recorded with an electrophysiolograph. The effect of ginsenoside Rb1 on ion channel currents, including the voltage-gated K + channel current (IK V ), calcium-activated potassium channel currents (IK Ca ), spontaneous transient outward currents and ATP-sensitive potassium channel current (IK ATP ), was recorded on freshly isolated single cells using the whole-cell patch clamp technique. RESULTS: Ginsenoside Rb1 dose-dependently inhibited the spontaneous contraction of intestinal smooth muscle by 21.15% ± 3.31%, 42.03% ± 8.23% and 67.23% ± 5.63% at concentrations of 25 μmol/L, 50 μmol/L and 100 μmol/L, respectively (n=5,P<0.05). The inhibitory effect of ginsenoside Rb1 on spontaneous contraction was significantly but incompletely blocked by 10 mmol/L tetraethylammonium or 0.5 mmol/L 4-aminopyridine, respectively (n=5, P<0.05). However, the inhibitory effect of ginsenoside Rb1 on spontaneous contraction was not affected by 10 μmol/L glibenclamide or 0.4 μmol/L tetrodotoxin. At the cell level, ginsenoside Rb1 increased outward potassium currents, and IK V was enhanced from 1137.71 ± 171.62 pA to 1449.73 ± 162.39 pA by 50 μmol/L Rb1 at +60 mV (n=6, P<0.05). Ginsenoside Rb1 increased IK Ca and enhanced the amplitudes of spontaneous transient outward currents from 582.77 ± 179.09 mV to 788.12 ± 278.34 mV (n=5, P<0.05). However, ginsenoside Rb1 (50 μmol/L) had no significant effect on IK ATP (n=3, P<0.05). CONCLUSION: These results suggest that ginsenoside Rb1 has an inhibitory effect on the spontaneous contraction of mouse intestinal smooth muscle mediated by the activation of IK V and IK Ca , but the K ATP channel was not involved in this effect.
文摘BACKGROUND In the first studies of electrochemotherapy(ECT),small cutaneous metastases were treated and only mild or moderate pain was observed;therefore,pain was not considered a significant issue.As the procedure began to be applied to larger cutaneous metastases,pain was reported more frequently.For that reason,reduction of both muscle contractions and pain have been investigated over the years.AIM To present an overview of different protocols described in literature that aim to reduce muscle contractions and pain caused by the electroporation(EP)effect in both ECT and irreversible EP treatments.METHODS Thirty-three studies published between January 1999 and November 2020 were included.Different protocol designs and electrode geometries that reduce patient pain and the number of muscle contractions and their intensity were analysed.RESULTS The analysis showed that both high frequency and bipolar/biphasic pulses can be used to reduce pain and muscle contractions in patients who undergo EP treatments.Moreover,adequate electrode design can decrease EP-related morbidity.Particularly,needle length,diameter and configuration of the distance between the needles can be optimised so that the muscle volume crossed by the current is reduced as much as possible.Bipolar/biphasic pulses with an inadequate pulse length seem to have a less evident effect on the membrane permeability compared with the standard pulse protocol.For that reason,the number of pulses and the voltage amplitude,as well as the pulse duration and frequency,must be chosen so that the dose of delivered energy guarantees EP efficacy.CONCLUSION Pain reduction in EP-based treatments can be achieved by appropriately defining the protocol parameters and electrode design.Most results can be achieved with high frequency and/or bipolar/biphasic pulses.However,the efficacy of these alternative protocols remains a crucial point to be assessed further.
基金supported by a Natural Science Foundation of China Grant(30770805)
文摘Muscle unloading due to long-term exposure of weightlessness or simulated weightlessness causes atrophy, loss of functional capacity, impaired locomotor coordination, and decreased resistance to fatigue in the antigravity muscles of the lower limbs. Besides reducing astronauts' mobility in space and on returning to a gravity environment, the molecular mechanisms for the adaptation of skeletal muscle to unloading also play an important medical role in conditions such as disuse and paralysis. The tail-suspended rat model was used to simulate the effects of weightlessness on skeletal muscles and to induce muscle unloading in the rat hindlimb. Our series studies have shown that the maximum of twitch tension and the twitch duration decreased significantly in the atrophic soleus muscles, the maximal tension of high-frequency tetanic contraction was significantly reduced in 2-week unloaded soleus muscles, however, the fatigability of highfrequency tetanic contraction increased after one week of unloading. The maximal isometric tension of intermittent tetanic contraction at optimal stimulating frequency did not alter in 1-and 2-week unloaded soleus, but significantly decreased in 4-week unloaded soleus. The 1-week unloaded soleus, but not extensor digitorum longus(EDL), was more susceptible to fatigue during intermittent tetanic contraction than the synchronous controls. The changes in K+ channel characteristics may increase the fatigability during high-frequency tetanic contraction in atrophic soleus muscles. High fatigability of intermittent tetanic contraction may be involved in enhanced activity of sarcoplasmic reticulum Ca2+-ATPase(SERCA) and switching from slow to fast isoform of myosin heavy chain, tropomyosin, troponin I and T subunit in atrophic soleus muscles. Unloaded soleus muscle also showed a decreased protein level of neuronal nitric oxide synthase(nNOS), and the reduction in nNOS-derived NO increased frequency of calcium sparks and elevated intracellular resting Ca2+ concentration([Ca2+]i) in unloaded soleus muscles. High [Ca2+]i activated calpain-1 which induced a higher degradation of desmin. Desmin degradation may loose connections between adjacent myofibrils and further misaligned Z-disc during repeated tetanic contractions. Passive stretch in unloaded muscle could preserve the stability of sarcoplasmic reticulum Ca2+ release channels by means of keeping nNOS activity, and decrease the enhanced protein level and activity of calpain to control levels in unloaded soleus muscles. Therefore, passive stretch restored normal appearance of Z-disc and resisted in part atrophy of unloaded soleus muscles. The above results indicate that enhanced fatigability of high-frequency tetanic contraction is associated to the alteration in K+ channel characteristics, and elevated SERCA activity and slow to fast transition of myosin heavy chain(MHC) isoforms increases fatigability of intermittent tetanic contraction in atrophic soleus muscle. The sarcomeric damage induced by tetanic contraction can be retarded by stretch in atrophic soleus muscles.
文摘Given recent technological developments, ultrasound Doppler can provide valuable measurements of blood velocity/flow in the conduit artery with high temporal resolution. In human-applied science such as exercise physiology, hemodynamic measurements in the conduit artery is commonly performed by blood flow feeding the exercising muscle, as the increase in oxygen uptake (calculated as a product of arterial blood flow to the exercising limb and the arterio-venous oxygen difference) is directly proportional to the work performed. The increased oxygen demand with physical activity is met through a central mechanism, an increase in cardiac output and blood pressure, as well as a peripheral mechanism, an increase in vascular conductance and oxygen extraction (a major part of the whole exercising muscles) from the blood. The increase in exercising muscle blood flow in relation to the target workload (quantitative response) may be one indicator in circulatory adjustment for the ac- tivity of muscle metabolism. Therefore, the determination of local blood flow dynamics (potential oxygen supply) feeding repeated (rhythmic) muscle contractions can contribute to the understanding of the factors limiting work capacity including, for instance, muscle metabolism, substance utilization and magnitude of vasodilatation in the exercising muscle. Using non-invasive measures of pulsed Doppler ultrasound, the validity of blood velocity/flow in the forearm or lower limb conduit artery feeding to the muscle has been previously demonstrated during rhythmic muscle exercise. For the evaluation of exercising blood flow, not only muscle contraction induced internal physiological variability, or fluctuations in the magnitude of blood velocity due to spontaneous muscle contraction and relaxation induced changes in force curve intensity, superimposed in cardiac beat-by-beat, but also the alterations in the blood velocity (external variability) due to a temporary sudden change in the achieved workload, compared to the target workload, should be considered. Furthermore, a small amount of inconsistency in the voluntary muscle contraction force at each kick seems to be unavoidable, and may influence exercising muscle blood flow, although subjects attempt to perform precisely similar repeated voluntary muscle contractions at target workload (muscle contraction force). This review presents the methodological considerations for the variability of exercising blood velocity/flow in the limb conduit artery during dynamic leg exercise assessed by pulsed Doppler ultrasound in relation to data previously reported in original research.
文摘We aimed to investigate the association between mobility and skeletal muscle strength by using magnetic resonance diffusion tensor imaging (DTI). This study included 20 healthy male volunteers (mean age, 21.8 ± 1.1 years). The maximum voluntary strength (MVC) of each participant was measured with the ankle joint in plantar and dorsal flexion using an instrument for measuring muscle strength. Moreover, magnetic resonance imaging (MRI) was performed with the ankle joint at rest, in plantar flexion, and in dorsal flexion. For imaging, a 1.5-T MRI device was used, and a diffusion-weighted stimulated echo-planar imaging pulse sequence. Tensor eigenvalues (λ), fractional anisotropy (FA), and the apparent diffusion coefficient (ADC) were calculated from data obtained by DTI. The resulting MRI data were compared to the data on muscle mobility or strength and statistically analyzed. Regarding changes in DTI indices during muscle movements, anisotropy of the tibialis anterior was significantly increased from rest to plantar flexion (P < 0.01), whereas no significant change was observed in dorsal flexion (n.s.). In contrast, the extent of significant changes in anisotropy of the medial gastrocnemius (mGC) and soleus (SOL) was small at plantar flexion (mGC, P < 0.01;SOL, n.s.), whereas the indices were significantly increased at dorsal flexion (P < 0.01). Regarding the correlation between MVC of each skeletal muscle and the DTI indices, FA and λ3 were significantly correlated in movements involving the muscles, whereas no significant correlation was observed in movements not involving them. Changes in intramuscular water molecules by elongation and contraction of the skeletal muscle fibers could be assumed to affect changes in diffusional anisotropy. When muscles contract, the space between myocytes was reduced and they might become increasingly dense. Moreover, diffusional anisotropy increased with increasing MVC, whereas ADC remained unchanged. DTI was suggested to produce measurements similar to the degree of muscle strength.
文摘We developed an eccentric contraction induced electrical stimulation (ES) training system. The purpose of this study was to investigate whether the eccentric contraction induced ES enhance the knee extension torque compared with typical ES. Twenty-two young untrained men (age: 23 ± 3 years) in the acute response trial (single training) and seven untrained men in the long period training trial (for 6 weeks) were studied. We measured muscle thickness and knee extension torque evoked by ES with eccentric contraction training system (ES + ECC) or ES alone for the quadriceps muscle of men. The levels of pain and discomfort were evaluated using numeric rating scale (NRS) and heart rate variability. The knee extension torque of ES + ECC was higher than that of ES alone in the acute response trial. There were no significant differences in the levels of pain and discomfort between ES and ES + ECC. Additionally, ES + ECC training for 6 weeks was effective on the quadriceps muscle thickness and knee extension torque. In contrast, the ES alone training failed to increase muscle thickness and knee extension torque. These results suggest that eccentric contraction induced ES would have the potential to become an effective intervention to promote muscle strengthening.
基金Supported by Council of Scientific and Industrial Research,Delhi
文摘AIM:To study the pharmacological profile and inhibition of smooth muscle contraction by YFa and its analogs in conjunction with their receptor selectivity. METHODS:The effects of YFa and its analogs (D-Ala2) YFa, Y (D-Ala2) GFMKKKFMRF amide and Des-Phe-YGGFMKKKFMR amide in guinea pig ileum (GPI) and mouse vas deferens (MVD) motility were studied using an isolated tissue organ bath system, and morphine and DynA (1-13) served as controls. Acetylcholine was used for muscle stimulation. The observations were validated by specific antagonist pretreatment experiments using naloxonazine, naltrindole and norbinaltor-phimine norBNI. RESULTS:YFa did not demonstrate significant inhibition of GPI muscle contraction as compared with mor-phine (15% vs 62%, P = 0.0002), but moderate inhibition of MVD muscle contraction, indicating the role of κ opioid receptors in the contraction. A moderate inhibition of GPI muscles by (Des-Phe) YFa revealed the role of anti-opiate receptors in the smooth muscle contraction. (D-Ala-2) YFa showed significant inhibition of smooth muscle contraction, indicating the involvement of mainly δ receptors in MVD contraction. These results were supported by specific antagonist pretreatment assays. CONCLUSION:YFa revealed its side-effect-free analgesic properties with regard to arrest of gastroin-testinal transit. The study provides evidences for the involvement of κ and anti-opioid receptors in smooth muscle contraction.
文摘The aim of this study was to determine the within-day and between-days reliability of surface electromyographic (EMG) power spectral analysis in assessing fatigability of the vastus medialis (VM) muscle during knee and hip flexion under constant load application. The subjects were 13 healthy adult men free of knee abnormalities. Surface EMG was recorded from vastus medialis obliquus (VMO) and vastus medialis longus (VML) during sustained isometric contractions at 60% of maximal voluntary contraction until exhaustion on the leg press machine (static leg press test). Linear regression analysis was applied to median frequency (MF) time series to calculate initial MF and MF slope. For VMO and VML, the initial MF showed moderate to high reliability, while the MF slope showed high reliability (Intraclass correlation coefficient (ICC) = initial MF: 0.63 - 0.92, MF slope: 0.70 - 0.86). The results demonstrated that spectral analysis of surface EMG recording during isometric VM muscle contraction has high within-day and between-days reliability in the assessment of fatigability of the VMO and VML.
