Maximal Contraction Force Research Articles

Origami-Inspired Bionic Soft Robot Stomach with Self-Powered Sensing.

The stomach is a vital organ in the human digestive system, and its digestive condition is critical to human health. The physical movement of the stomach during digestion is controlled by the circular and oblique muscles. Existing stomach simulators are unable to realistically reproduce the physical movement of the stomach. Due to the complexity of gastric motility, it is challenging to simulate and sense gastric motility. This study proposes for the first time a bionic soft robotic stomach (BSRS) with an integrated drive and sensing structure inspired by origami and self-powered sensing technology. This soft stomach (SS) can realistically simulate and sense the movements of various parts of the human stomach in real-time. The contraction force and contraction rate of the BSRS are investigated with different viscosity contents, and the experimental values are similar to the physiological range (maximum contraction force is 3.2 N, and maximum contraction rate is 0.8). This paper provides an experimental basis for the study of gastric digestive medicine and food science by simulating the peristaltic motion of the BSRS according to the human stomach and by combining the triboelectric nanogenerator (TENG) sensing technology to monitor the motion of the BSRS in real-time.

The impact of cerebellar transcranial direct current stimulation on isometric bench press performance in trained athletes

Athletic development centers on optimizing performance, including technical skills and fundamental motor abilities such as strength and speed. Parameters such as maximum contraction force and rate of force development, influence athletic success, although performance gains become harder to achieve as athletic abilities increase. Non-invasive transcranial direct current stimulation of the cerebellum (CB-tDCS) has been used successfully to increase force production in novices, although the potential effects in athletes remain unexplored. The present study examined the effects of CB-tDCS on maximum isometric voluntary contraction force (MVCiso) and isometric rate of force development (RFDiso) during a bench press task in well-trained athletes. 21 healthy, male, strength-trained athletes participated in a randomized, sham-controlled, double-blinded crossover design. Each participant completed the isometric bench press (iBP) task on two separate days, with at least 5 days between sessions, while receiving either CB-tDCS or sham stimulation. Electromyography (EMG) recordings of three muscles involved in iBP were acquired bilaterally to uncover differences in neuromuscular activation and agonist-antagonist co-contraction between conditions. Contrary to our hypothesis, no significant differences in MVCiso and RFDiso were observed between CB-tDCS and sham conditions. Furthermore, no tDCS-induced differences in neuromuscular activation or agonist-antagonist co-contraction were revealed. Here, we argue that the effects of CB-tDCS on force production appear to depend on the individual's training status. Future research should study individual differences in tDCS responses between athletes and novices, as well as the potential of high-definition tDCS for precise brain region targeting to potentially enhance motor performance in athletic populations.

The effect of C60 fullerenes on the recovery of muscle soleus contraction dynamics in rats after chronic alcoholization

Background. It has been shown that the available therapeutic agents do not eliminate the consequences of miotic pathologies in chronic alcoholism, the most significant of which are disturbances in the dynamics of muscle contraction. A positive effect of biocompatible water-soluble C60 fullerenes on the contraction parameters of damaged muscles has been established. In addition, administration of C60 fullerene aqueous solution during chronic alcoholization of rats protects muscle tissue from damage caused by oxidative stress. Materials and Methods. Biomechanical parameters such as the values of the minimum and maximum contraction force and the muscle force impulse were evaluated using tensometry. The blood levels of creatine phosphokinase and lactate dehydrogenase, creatinine and lactate as well as the level of oxidative processes in muscle tissue of experimental animals (content of hydrogen peroxide, activity of catalase, glutathione peroxidase and superoxide dismutase) as markers of muscle damage were determined using methods of biochemical analysis. Results. The C60 fullerene aqueous solution effect on the skeletal muscle contraction dynamics in rats after chronic alcoholization for 9 months and cessation of alcohol consumption for 1 month was investigated. It was established that water-soluble C60 fullerenes (daily dose of 1 mg/kg) reduce the effects of chronic alcoholization by 35–40±2 % on the studied biomechanical parameters and by 20±1 % on the studied biochemical parameters compared to the group of alcoholized animals, thus increasing the energy capabilities of the muscular system. Conclusions. The obtained data indicate a pronounced protective effect of C60 fullerenes on the muscle soleus contraction dynamics during the development of alcoholic myopathy, which opens up the potential possibility of their use for the prevention and correction of miotic damage.

An electrical stimulation intervention protocol to prevent disuse atrophy and muscle strength decline: an experimental study in rat

BackgroundSkeletal muscle is negatively impacted by conditions such as spaceflight or prolonged bed rest, resulting in a dramatic decline in muscle mass, maximum contractile force, and muscular endurance. Electrical stimulation (ES) is an essential tool in neurophysiotherapy and an effective means of preventing skeletal muscle atrophy and dysfunction. Historically, ES treatment protocols have used either low or high frequency electrical stimulation (LFES/HFES). However, our study tests the use of a combination of different frequencies in a single electrical stimulation intervention in order to determine a more effective protocol for improving both skeletal muscle strength and endurance.MethodsAn adult male SD rat model of muscle atrophy was established through 4 weeks of tail suspension (TS). To investigate the effects of different frequency combinations, the experimental animals were treated with low (20 Hz) or high (100 Hz) frequency before TS for 6 weeks, and during TS for 4weeks. The maximum contraction force and fatigue resistance of skeletal muscle were then assessed before the animals were sacrificed. The muscle mass, fiber cross-sectional area (CSA), fiber type and related protein expression were examined and analyzed to gain insights into the mechanisms by which the ES intervention protocol used in this study regulates muscle strength and endurance.ResultsAfter 4 weeks of unloading, the soleus muscle mass and fiber CSA decreased by 39% and 58% respectively, while the number of glycolytic muscle fibers increased by 21%. The gastrocnemius muscle fibers showed a 51% decrease in CSA, with a 44% decrease in single contractility and a 39% decrease in fatigue resistance. The number of glycolytic muscle fibers in the gastrocnemius also increased by 29%. However, the application of HFES either prior to or during unloading showed an improvement in muscle mass, fiber CSA, and oxidative muscle fibers. In the pre-unloading group, the soleus muscle mass increased by 62%, while the number of oxidative muscle fibers increased by 18%. In the during unloading group, the soleus muscle mass increased by 29% and the number of oxidative muscle fibers increased by 15%. In the gastrocnemius, the pre-unloading group showed a 38% increase in single contractile force and a 19% increase in fatigue resistance, while in the during unloading group, a 21% increase in single contractile force and a 29% increase in fatigue resistance was observed, along with a 37% and 26% increase in the number of oxidative muscle fibers, respectively. The combination of HFES before unloading and LFES during unloading resulted in a significant elevation of the soleus mass by 49% and CSA by 90%, with a 40% increase in the number of oxidative muscle fibers in the gastrocnemius. This combination also resulted in a 66% increase in single contractility and a 38% increase in fatigue resistance.ConclusionOur results indicated that using HFES before unloading can reduce the harmful effects of muscle unloading on the soleus and gastrocnemius muscles. Furthermore, we found that combining HFES before unloading with LFES during unloading was more effective in preventing muscle atrophy in the soleus and preserving the contractile function of the gastrocnemius muscle.

Montelukast, a LRRC8A inhibitor, decreases the contractile response to Endothelin-1 in the vaginal smooth muscle of aged mice

Introduction: Vaginal smooth muscle (VaSM) is an important contributor to female sexual function, desire, and arousal. Increased vaginal blood flow via vasodilation of the vaginal blood vessels is key to the of lubrication and creating an enjoyable sexual experience. Female sexual dysfunction (FSD) is common in hypertensive and diabetic women, as well as many who suffer from hormonal imbalances, including menopause. Despite the substantial population that suffers from FSD, research into the mechanisms and non-hormonal treatments are limited. Leucine rich repeat containing channel 8A (LRRC8A) is a volume regulated anion channel (VRAC) that regulates Nox1 and can modulate the extracellular production of superoxide (O2∙-). In aged tissues, there are increased in extracellular ROS production as well as vascular and smooth muscle dysfunction. The objective of these experiments is to elucidate the mechanisms behind female sexual dysfunction that present with vascular and smooth muscle dysfunction and determine if the LRRC8A inhibitor, Montelukast, can alleviate some of the symptoms of FSD and improve quality of life. In this study, we hypothesize that the inhibition of LRRC8A in will decrease the contraction to Endothelin-1 in the vaginal smooth muscle of the aged mice. Methods: Aged (16 mo and 20 mo old) female lean mice underwent distal vaginal dissection. Vaginal tissue was cleaned and mounted on a strip myograph in Krebs solution and the contraction elicited by Endothelin-1 was performed in the absence and repeated in the presence of the LRRC8A inhibitor, Montelukast (1uM) after a 30-minute incubation. Data was analyzed using Prism. The maximal contraction in the absence of the inhibitor was taken as 100%, and the contraction in the presence of the inhibitor was calculated as a percentage of the maximal contraction attained in the absence of the inhibitor. Results: Contraction induced by Endothelin-1 (10-12 M to 3✕10 -8 M) alone compared to in the presence of Montelukast (1 uM) showed that Montelukast decreased both the potency and the maximum force of contraction in the aged VaSM. After incubation with 1 mM Montelukast, the EC50 and Emax were significantly different (0.0430 and <0.0001, respectively). Conclusion: This is the first study investigating the vaginal smooth muscle from the perspective of ROS production and the influence of LRRC8A in aged animals. The change in the contractile response in the treated animals may be due to the modulation of the production of O2∙-. Patients that suffer from FSD are a large and overlooked community in need of new therapeutic approaches. Treatment with LRRC8A offers a potential novel approach to treat FSD and should be further researched to observe its overall impact in FSD. 1R01DK132948-01, SMSNA Student Grant This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Acute Biomechanical Effects of Empagliflozin on Living Isolated Human Heart Failure Myocardium

PurposeMultiple randomized controlled trials have presented SGLT2 inhibitors (SGLT2i) as novel pharmacological therapy for patients with heart failure, resulting in reductions in hospitalization for heart failure and mortality. Given the absence of SGLT2 receptors in the heart, mechanisms of direct cardioprotective effects of SGLT2i are complex and remain to be investigated. In this study, we evaluated the direct biomechanical effects of SGLT2i empagliflozin on isolated myocardium from end-stage heart failure patients.MethodsVentricular tissue biopsies obtained from 7 patients undergoing heart transplantation or ventricular assist device implantation surgery were cut into 27 living myocardial slices (LMS) and mounted in custom-made cultivation chambers with mechanical preload and electrical stimulation, resulting in cardiac contractions. These 300 µm thick LMS were subjected to 10 µM empagliflozin and with continuous recording of biomechanical parameters.ResultsEmpagliflozin did not affect the maximum contraction force of the slices, however, increased total contraction duration by 13% (p = 0.002) which was determined by prolonged time to peak and time to relaxation (p = 0.009 and p = 0.003, respectively).ConclusionThe addition of empagliflozin to LMS from end-stage heart failure patients cultured in a biomimetic system improves contraction and relaxation kinetics by increasing total contraction duration without diminishing maximum force production. Therefore, we present convincing evidence that SGLT2i can directly act on the myocardium in absence of systemic influences from other organ systems.

Atrial cardiomyocytes from a canine model of atrial fibrillation demonstrate reduced force development and altered expression of contractile proteins.

Atrial fibrillation (AF) is the most common cardiac rhythm disturbance and associates with worse outcomes in cardiac contractile-related diseases including cardiomyopathy. As most studies surrounding AF focus on the electrophysiology of the disease, there is little known about cardiomyocyte contractile function in AF. We used atrial tissue from an established atrial tachypacing canine model of AF. Whole protein lysates were collected from the atria to conduct mass spectrometry analysis showing dysregulation of numerous molecular pathways, including contractility. Skinned atrial cardiomyocytes were isolated from the tissue for force calcium and passive tension experiments. Force calcium experiments showed a significant reduction in the maximum force of contraction of AF cardiomyocytes. To explain this, myosin heavy chain (MHC) isoform expression was evaluated because isoform switching is known to alter force of contraction. Decreased percent beta expression was found, explaining the reduction of force due to MHC alpha's capacity for reduced force of contraction. AF cardiomyocytes showed increased calcium sensitivity of force development, which may translate to prolonged contraction with slower relaxation in vivo. A significant reduction in S100A1 was seen in the AF samples via mass spectrometry, which is associated with increased calcium sensitivity. Prolonged contraction along with reduced force of each contraction could support the development of atrial clots. Atrial cardiomyocytes from the AF hearts demonstrated a significant reduction in the passive tension. Evaluation of titin isoform expression, which is known to alter passive tension, showed increased titin degradation, supporting the capacity for atrial dilation in vivo. Discerning the role of contractility in the pathology of atrial fibrillation could provide novel avenues of AF treatment, especially in instances where it is associated with contractile diseases.

Comparison of arterial storage conditions for delayed arterial ring testing

ObjectiveArterial ring testing is the gold standard for measuring arterial function. Increased arterial tone through arterial contraction and impaired endothelial relaxation (endothelial dysfunction) are key metrics of impaired arterial health in peripheral arterial disease (PAD). To allow for comparative testing of arteries during standard laboratory hours, storage buffers and conditions have been used to extend the functional life of arteries. Various storage conditions have been compared, but there has not been a robust comparison or validation in human arteries. The objective of this work is to optimize storage of arterial segments for endothelial cell (EC) testing in a murine model and to test EC function in human PAD arteries. We hypothesized that certain storage conditions would be superior to others. MethodsHealthy murine aortas were harvested from 10- to 14-week-old C57/Bl6J male and female mice and compared under different storage protocols (24 hours) to immediate arterial testing. The storage conditions tested were: Opti-MEM (37°C or 4°C), Krebs-HEPES with 1.8 mmol/L or 2.5 mmol/L calcium (4°C), or Wisconsin (WI) solution at 4°C. Vascular function was evaluated by isometric force testing. Endothelium-dependent and -independent relaxation were measured after precontraction with addition of methacholine or sodium nitroprusside, respectively. Arterial contraction was stimulated with potassium chloride or phenylephrine. Analysis of variance was used to determine significance compared with immediate testing with P < .05. Under institutional review board approval, 28 PAD arteries were collected at amputation and underwent vascular function testing as described. Disturbed flow conditions were determined by indirect (upstream occlusion) flow to the harvested tibial arteries. Stable flow arteries had in-line flow. Arterial calcification was quantified manually as present or not present. ResultsWe found that 4°C WI and 37°C Opti-MEM best preserved endothelium-dependent relaxation and performed similarly to immediately testing aortas (termed fresh for freshly tested) (P > .95). Other storage conditions were inferior to freshly tested aortas (P < .05). Vascular smooth muscle function was tested by endothelial-independent relaxation and contractility. All storage conditions preserved endothelial-independent relaxation and contractility similar to freshly tested arteries. However, 4°C WI and 37°C Opti-MEM storage conditions most closely approximated the maximum force of contraction of freshly tested arteries in response to potassium chloride (P > .39). For human arterial testing, 28 tibial arteries were tested for relaxation and contraction with 16 arteries with peripheral artery occlusive disease (PAD with disturbed flow) and 12 without peripheral artery occlusive disease (PAD with stable flow), of which 14 were calcified and 14 were noncalcified. Endothelial-dependent relaxation data was measurable in 9 arteries and arterial contraction data was measurable in 14 arteries. When comparing flow conditions, arteries exposed to disturbed flow (n = 4) had significantly less relaxation (2% vs 59%; P = .03) compared with stable flow conditions (n = 5). In contrast, presence the (n = 6) or absence of calcification (n = 3) did not impact arterial relaxation. Arterial contraction was not different between groups in either comparison by flow (n = 9 disturbed; n = 5 stable) or calcification (n = 6 present; n = 8 absent). ConclusionsIn healthy murine aortas, arterial storage for 24 hours in 4°C WI or 37°C Opti-MEM both preserved endothelium-dependent relaxation and maximum force of contraction. In human PAD arteries stored in 4° WI, flow conditions before arterial harvest, but not arterial calcification, led to differences in arterial relaxation in human PAD arteries. Arterial contractility was more robust (11/28 arteries) compared with arterial relaxation (7/28 arteries), but was not significantly different under flow or calcification parameters. This work defines ideal storage conditions for arterial ring testing and identifies that EC dysfunction from disturbed flow may persist in delayed ex vivo arterial testing.

Effect of 40 Hz Magnetic Field Application in Posttraumatic Muscular Atrophy Development on Muscle Mass and Contractions in Rats

Muscle atrophy refers to the deterioration of muscle tissue due to a long-term decrease in muscle function. In the present study, we simulated rectus femoris muscle atrophy experimentally and investigated the effect of pulsed electromagnetic field (PEMF) application on the atrophy development through muscle mass, maximal contraction force, and contraction-relaxation time. A quadriceps tendon rupture with a total tenotomy was created on the rats' hind limbs, inhibiting knee extension for 6 weeks, and this restriction of the movement led to the development of disuse atrophy, while the control group underwent no surgery. The operated and control groups were divided into subgroups according to PEMF application (1.5 mT for 45 days) or no PEMF. All groups were sacrificed after 6 weeks and had their entire rectus femoris removed. To measure the contraction force, the muscles were placed in an organ bath connected to a transducer. As a result of the atrophy, muscle mass and strength were reduced in the operated group, while no muscle mass loss was observed in the operated PEMF group. Furthermore, measurements of single, incomplete and full tetanic contraction force and contraction time (CT) did not change significantly in the operated group that received the PEMF application. The PEMF application prevented atrophy resulting from 6 weeks of immobility, according to the contraction parameters. The effects of PEMF on contraction force and CT provide a basis for further studies in which PEMF is investigated as a noninvasive therapy for disuse atrophy development. © 2022 Bioelectromagnetics Society.

P.31 A multiparametric quantitative NMR study at rest and during exercise in subjects between 22 and 65 years of age: Preliminary results

The progressive decline in muscle strength and performance during ageing negatively affects the quality of life in the elderly and increases the risk of falls, disability and frailty. The age-related loss of muscle mass, strength and quality is a multifactorial process whose mechanisms are incompletely understood. Nuclear magnetic resonance (NMR) allows evaluating anatomical, structural and physiological aspects of muscle tissue non-invasively. Functional NMR also enables, for instance, to image during an exercise paradigm the tissue blood flow (BF) or energy metabolism using ³¹P MR spectroscopy (MRS). Here, we designed a protocol where multiple quantitative and complementary biomarkers were acquired in the lower leg in a single exam. Acquisitions were done at 3 T (Siemens Prisma) on 26 subjects (22 to 65 y.o., 15 women). Variables studied were muscle-specific cross-sectional area (CSA), intramuscular fat fraction (FF), muscle water T1 (T1_H2O) and T2 (T2_H2O ) values; and pH and concentrations of phosphocreatine (PCr), inorganic phosphate (Pi), phosphodiesters (PDE) and phosphomonoesters (PME) in the triceps. Dynamic simultaneous BF, T2* and 31P MRS measurements were done during a 13-min plantar flexion exercise. A linear model and ANOVA using gender and age as fixed factors were used for analysis. Preliminary results showed several statistically significant (p < 0.05) changes related to age: increased T1_H2O and FF in all the lower leg muscles (gastroc. med. & lat., soleus, tibial. ant. & post, peron.); increased PDE/ATP and PME/ATP ratios; and a modest CSA increase of the extensor and fibular muscles (unlike the quadriceps muscles). Pi/PCr at the end of exercise increased with age in male subjects. No other age-related changes were found for functional NMR variables, grip strength or triceps maximal contraction force. Our results show that age-related structural and basal metabolic changes can be observed with a multiparametric NMR approach in the muscle. The ongoing recruitment of additional subjects will allow us to confirm our findings.

Analysis of Biomechanical and Biochemical Markers of Rat Muscle Soleus Fatigue Processes Development during Long-Term Use of C60 Fullerene and N-Acetylcysteine.

The development of an effective therapy aimed at restoring muscle dysfunctions in clinical and sports medicine, as well as optimizing working activity in general remains an urgent task today. Modern nanobiotechnologies are able to solve many clinical and social health problems, in particular, they offer new therapeutic approaches using biocompatible and bioavailable nanostructures with specific bioactivity. Therefore, the nanosized carbon molecule, C60 fullerene, as a powerful antioxidant, is very attractive. In this study, a comparative analysis of the dynamic of muscle soleus fatigue processes in rats was conducted using 50 Hz stimulation for 5 s with three consistent pools after intraperitoneal administration of the following antioxidants: C60 fullerene (a daily dose of 1 mg/kg one hour prior to the start of the experiment) and N-acetylcysteine (NAC; a daily dose of 150 mg/kg one hour prior to the start of the experiment) during five days. Changes in the integrated power of muscle contraction, levels of the maximum and minimum contraction force generation, time of reduction of the contraction force by 50% of its maximum value, achievement of the maximum force response, and delay of the beginning of a single contraction force response were analyzed as biomechanical markers of fatigue processes. Levels of creatinine, creatine phosphokinase, lactate, and lactate dehydrogenase, as well as pro- and antioxidant balance (thiobarbituric acid reactive substances, hydrogen peroxide, reduced glutathione, and catalase activity) in the blood of rats were analyzed as biochemical markers of fatigue processes. The obtained data indicate that applied therapeutic drugs have the most significant effects on the 2nd and especially the 3rd stimulation pools. Thus, the application of C60 fullerene has a (50–80)% stronger effect on the resumption of muscle biomechanics after the beginning of fatigue than NAC on the first day of the experiment. There is a clear trend toward a positive change in all studied biochemical parameters by about (12–15)% after therapeutic administration of NAC and by (20–25)% after using C60 fullerene throughout the experiment. These findings demonstrate the promise of using C60 fullerenes as potential therapeutic nanoagents that can reduce or adjust the pathological conditions of the muscular system that occur during fatigue processes in skeletal muscles.

Different K+-release in distal myogenic and neurogenic muscular weakness during non-ischemic exercise

IntroductionIn myotonic dystrophy, an increased potassium release upon ischemic forearm exercise has been previously described. However, it remains unclear whether this is specific for myotonic dystrophies or just due to distal muscular weakness. MethodsNon-ischemic forearm test (NIFET) was performed and venous K+ concentration was measured at rest and at three different force levels (20–30%, 50–60%, 70–80%) related to maximal contraction force (MCF) in patients with distal myogenic (n = 7), neurogenic (n = 7) muscular weakness and healthy volunteers (n = 12). The specific K+ release was defined as K+ increase related to workload as force-time-integral during repetitive contraction. ResultsWorkload was lower at all force levels in both disease groups compared to the control group. With increasing workload, the K+ concentrations increased in all study groups. Analysing individual force levels related to the maximum contraction force (MCF), a higher specific K+ release was measured at low force levels in myopathies (20–30% MCF) in comparison to higher force levels (p = 0.02). At 20–30% MCF, the specific K+ release was significantly higher in myogenic compared to neurogenic muscular weakness (p = 0.005). At 50–60% and 70–80% MCF, the specific K+ values converged and did not significantly differ between the three groups (p = 0.09 and p = 0.37). DiscussionAt low force levels, K+ efflux related to workload is higher in patients with myogenic in comparison to neurogenic distal paresis. Our results indicate a different regulation of K+ balance in neurogenic and myogenic muscular weakness possibly due to a different recruitment behaviour of motor units and the firing rate of motor neurons.

P 45. Different K+-release in distal myopathy and motor neuropathy during non-ischemic exercise

Background. In myotonic dystrophy, a significantly increased potassium release upon exercise was previously described. However, it remained unclear so far whether this is a specific feature of myotonic dystrophies or a consequence of distal muscular weakness in general. Methods. We performed non-ischemic forearm exercise test (NIFET) and measured venous K + concentration at rest and at three different force levels (20–30%, 50–60%, 70–80%) related to maximal contraction force (MCF) in patients with different myopathies ( n = 7), motor neuropathies ( n = 8) with distal phenotype and healthy volunteers ( n = 12). The specific K + production was defined as venous K+ increase related to workload. Results. Maximal contraction force, workload and venous K + increase were lower at all force levels in both myopathy and neuropathy groups compared to the control group. With increasing workload, the control group showed a quasi-linear increase in K + release, resulting in a nearly constant specific K + production within the three force levels ( p = 0.752, Kruskal-Wallis-Test). In contrast, in myopathies a higher specific K + production was measured at low force levels (20-30% MCF) in comparison to higher force levels ( p = 0.015, Kruskal-Wallis test). In neuropathies, the lowest specific K + production was obtained at 20–30% MCF. At this force level, the specific K + production was significantly higher in myopathies compared to neuropathies (Fig. 1; p = 0.005, Mann-Whitney U Test). At 50–60% and 70–80% MCF, the specific K + values increasingly converged and did not significantly differ between the three groups (Fig. 1; p = 0.09 and p = 0.37, Kruskal-Wallis test). Conclusion. In our study, increased K + efflux related to workload occurred in patients with myogenic in comparison to neurogenic distal muscular weakness at low force levels. High specific K + production does not seem to be an exclusive feature of myotonic dystrophies but of myogenic muscular weakness in general. Our results point to a different regulation of K+ balance in neurogenic and myogenic muscular weakness possibly due to a different recruitment behaviour of motor units and the action potential frequency of motor neurons in neurogenic and myogenic processes. Fig. 1.

Experimentally Identified Models of McKibben Soft Actuators as Primary Movers and Passive Structures

Abstract Soft robots join body and actuation, forming their structure from the same elements that induce motion. Soft actuators are commonly modeled or characterized as primary movers, but their second role as support structure introduces strain–pressure combinations outside of normal actuation. This article examines a more complete set of possible strain–pressure combinations for McKibben actuators, including passive or unpressurized, deformation, pressurized extension and compression of a pressurized actuator beyond the maximum actuation strain. Each region is investigated experimentally, and empirical force–displacement–pressure relationships are identified. Particular focus is placed on ensuring that empirical relationships are consistent at boundaries between an actuator’s strain–pressure regions. The presented methodology is applied to seven McKibben actuator designs, which span variations in wall thickness, enclosure material, and actuator diameter. Empirical results demonstrate a trade-off between maximum contraction strain and force required to passively extend. The results also show that stiffer elastomers require an extreme increase in pressure to contract without a compensatory increase in maximum achieved force. Empirical force–displacement–pressure models were developed for each variant across all the studied strain–pressure regions, enabling future design variation studies for soft robots that use actuators as structures.

Fast skeletal myosin-binding protein-C regulates fast skeletal muscle contraction

Fast skeletal myosin-binding protein-C (fMyBP-C) is one of three MyBP-C paralogs and is predominantly expressed in fast skeletal muscle. Mutations in the gene that encodes fMyBP-C, MYBPC2, are associated with distal arthrogryposis, while loss of fMyBP-C protein is associated with diseased muscle. However, the functional and structural roles of fMyBP-C in skeletal muscle remain unclear. To address this gap, we generated a homozygous fMyBP-C knockout mouse (C2-/-) and characterized it both in vivo and in vitro compared to wild-type mice. Ablation of fMyBP-C was benign in terms of muscle weight, fiber type, cross-sectional area, and sarcomere ultrastructure. However, grip strength and plantar flexor muscle strength were significantly decreased in C2-/- mice. Peak isometric tetanic force and isotonic speed of contraction were significantly reduced in isolated extensor digitorum longus (EDL) from C2-/- mice. Small-angle X-ray diffraction of C2-/- EDL muscle showed significantly increased equatorial intensity ratio during contraction, indicating a greater shift of myosin heads toward actin, while MLL4 layer line intensity was decreased at rest, indicating less ordered myosin heads. Interfilament lattice spacing increased significantly in C2-/- EDL muscle. Consistent with these findings, we observed a significant reduction of steady-state isometric force during Ca2+-activation, decreased myofilament calcium sensitivity, and sinusoidal stiffness in skinned EDL muscle fibers from C2-/- mice. Finally, C2-/- muscles displayed disruption of inflammatory and regenerative pathways, along with increased muscle damage upon mechanical overload. Together, our data suggest that fMyBP-C is essential for maximal speed and force of contraction, sarcomere integrity, and calcium sensitivity in fast-twitch muscle.

Use of Ballistocardiography to Monitor Cardiovascular Hemodynamics in Preeclampsia.

Objective: Pregnancy requires a complex physiological adaptation of the maternal cardiovascular system, which is disrupted in women with pregnancies complicated by preeclampsia, putting them at higher risk of future cardiovascular events. The measurement of body movements in response to cardiac ejection via ballistocardiogram (BCG) can be used to assess cardiovascular hemodynamics noninvasively in women with preeclampsia.Methods: Using a previously validated, modified weighing scale for assessment of cardiovascular hemodynamics through measurement of BCG and electrocardiogram (ECG) signals, we collected serial measurements throughout pregnancy and postpartum and analyzed data in 30 women with preeclampsia and 23 normotensive controls. Using BCG and ECG signals, we extracted measures of cardiac output, J-wave amplitude × heart rate (J-amp × HR). Mixed-effect models with repeated measures were used to compare J-amp × HRs between groups at different time points in pregnancy and postpartum.Results: In normotensive controls, the J-amp × HR was significantly lower early postpartum (E-PP) compared with the second trimester (T2; p = 0.016) and third trimester (T3; p = 0.001). Women with preeclampsia had a significantly lower J-amp × HR compared with normotensive controls during the first trimester (T1; p = 0.026). In the preeclampsia group, there was a trend toward an increase in J-amp × HR from T1 to T2 and then a drop in J-amp × HR at T3 and further drop at E-PP.Conclusions: We observe cardiac hemodynamic changes consistent with those reported using well-validated tools. In pregnancies complicated by preeclampsia, the maximal force of contraction is lower, suggesting lower cardiac output and a trend in hemodynamics consistent with the hyperdynamic disease model of preeclampsia.

Measurement of maximal muscle contraction force induced by high-frequency magnetic stimulation: a preliminary study on the identification of the optimal stimulation site.

To identify the optimal stimulation site and technique for inducing strong muscle contraction using a high-frequency magnetic stimulator. High-frequency magnetic stimulation was administered to the right vastus lateralis (VL) of eight healthy adults at maximal intensity within the range of tolerable pain. The stimulation sites were as follows: section A, the area between the lateral edge of the base of the patella (LEBP) and the distal one-third of the thigh (point D); section B, the area between point D and the proximal one-third of the thigh (point P). Isometric maximal muscle contraction forces induced by magnetic stimulation (Stim-MCF) were compared between the two sections. The Stim-MCF was significantly higher in section B than in section A. Additionally, the sites susceptible to stimulation were confined to a narrow area near point D in section A and the central part between points D and P in section B. The degree of pain was very low in both sections. The optimal site for magnetic stimulation of the VL was limited to the central part of the thigh. In addition to the superficial proximal sub-branch, the deep proximal sub-branch and/or deeply clustered motor nerve endings may have been stimulated. Our results suggested that moving the probe was a useful way to identify the site that elicited the strongest muscle contraction force.

Hind Foot Drumming: Muscle Architecture of the Hind Limb in Three Bathyergidae Species

The relationship between muscle architectural properties and hind foot drumming of African mole-rats has yet to be determined using established methodology. Therefore, the internal structure of 32 hind limb muscles was evaluated in two drumming and one non-drumming species of Bathyergidae. The muscle mass (MM), fascicle length (Lf), and angle of pennation were measured to calculate the physiological cross-sectional area (PCSA) as well as estimate the maximum isometric force of contraction (Fmax). The most significant differences for the various muscle architecture parameters analyzed in synergistic muscle groups and individual muscles were observed between the rapid drumming Georychus capensis and the non-drumming Cryptomys hottentotus natalensis. The PCSA values of the hip extensors, hip adductors, knee extensors, and knee flexors of G. capensis were significantly larger than that of C. h. natalensis. Additionally, the hip extensors and knee flexors of both the drumming species (G. capensis and Bathyergus suillus) were shown to be capable of higher power output compared to the non-drumming species, and the hip adductors of G. capensis capable of faster contraction. M. gracilis anticus may play a key role in facilitating hind foot drumming as it was the only muscle to be significantly different in G. capensis and C. h. natalensis for all three muscle architecture parameters analyzed. Furthermore, it features in the high shortening capacity quadrant of the functional space plot of both G. capensis and B. suillus but not the non-drumming C. h. natalensis.

Hot Tearing Behavior in Double Ternary Eutectic Alloy System: Mg-Ce-Al Alloys

The hot tearing behavior of the double ternary eutectic alloy system, Al-6Mg-xSi (0 to 6.0 wt pct Si) alloys, was evaluated by a constrained rod casting mold equipped with a thermocouple and a load cell connected to a data acquisition system. Experimental results were compared with the results calculated by Scheil’s model using Pandat software to predict the occurrence of hot tearing in Al-6Mg-xSi alloys. The curve of hot tearing susceptibility contained two peaks, which were mainly affected by the double ternary eutectic reactions and the solidification phases evolution. And it agreed with the Kou’s hot tearing index precisely. The types and fractions of solidification phases (Al3Mg2, Mg2Si, and eutectic Si) determined by the addition of Si content changed the freezing range and eutectic liquid fraction greatly. In addition, the types, fractions, sizes, and distributions of solidification phases affected the nucleation, propagation, and healing of hot tear cracks. The maximum contraction force value decreased as the reduction of volume shrinkage coefficient due to the addition of Si content. The drop-in force value on the contraction force curve could indicate the occurrence of hot tearing, and predict the hot tearing susceptibility when considering the shrinkage coefficient.

Effects of Trans-Cinnamaldehyde on Reperfused Ischemic Skeletal Muscle and the Relationship to Laminin

Purpose Ischemia-reperfusion (I-R) injury is a serious problem caused by vascular trauma, tourniquet use and/or compartment syndrome. Studies have reported that skeletal muscle function is impaired due to the lower extremity I-R injury. There are insufficient studies on the treatment methods used for the recovery of dysfunction. This study is designed to investigate the effects of trans-cinnamaldehyde (TCA), a volatile oil of cinnamon structure, on the contractile dysfunction due to I-R injury of rat extensor-digitorum-longus (EDL) muscle. Materials and methods Sprague-Dawley rats were randomly divided into three groups. Except for the animals in the control group, all animals received saline (3-ml/kg) or TCA solution (30-mg/kg) which was administered orally three times with an 8-h interval before ischemia. After 24-hours, experimental groups were subjected to 3-h of lower extremity ischemia followed by 5-h reperfusion period. Then, the compound muscle action potential (CMAP) and mechanical activity of muscle were recorded using the standard electro-biophysical techniques. Results There was a decrease in the maximum contractile force in I-R group compared to the control group (p < 0.05). Oxidative damage indicator (MDA) and antioxidant indicator (CAT) increased in the EDL muscle and serum samples in the I-R group (p < 0.05). Laminin expression showed a reduction in the I-R group (p < 0.05). It was seen that TCA achieve again the maximum contraction force in the EDL muscle (p < 0.05) and maintain the expression of laminin (p > 0.05). Conclusion We concluded that TCA has a potential protective effect with antioxidant effects against I-R injury and may maintain laminin levels.