Modulation Of Contraction Research Articles

Effects of older age on contraction-induced intramyocellular acidosis and inorganic phosphate accumulation in vivo: A systematic review and meta-analysis.

Although it is clear that the bioenergetic basis of skeletal muscle fatigue (transient decrease in peak torque or power in response to contraction) involves intramyocellular acidosis (decreased pH) and accumulation of inorganic phosphate (Pi) in response to the increased energy demand of contractions, the effects of old age on the build-up of these metabolites has not been evaluated systematically. The purpose of this study was to compare pH and [Pi] in young (18-45 yr) and older (55+ yr) human skeletal muscle in vivo at the end of standardized contraction protocols. Full study details were prospectively registered on PROSPERO (CRD42022348972). PubMed, Web of Science, and SPORTDiscus databases were systematically searched and returned 12 articles that fit the inclusion criteria for the meta-analysis. Participant characteristics, contraction mode (isometric, dynamic), and final pH and [Pi] were extracted. A random-effects model was used to calculate the mean difference (MD) and 95% confidence interval (CI) for pH and [Pi] across age groups. A subgroup analysis for contraction mode was also performed. Young muscle acidified more than older muscle (MD = -0.12 pH; 95%CI = -0.18,-0.06; p<0.01). There was no overall difference by age in final [Pi] (MD = 2.14 mM; 95%CI = -0.29,4.57; p = 0.08), although sensitivity analysis revealed that removing one study resulted in greater [Pi] in young than older muscle (MD = 3.24 mM; 95%CI = 1.72,4.76; p<0.01). Contraction mode moderated these effects (p = 0.02) such that young muscle acidified (MD = -0.19 pH; 95%CI = -0.27,-0.11; p<0.01) and accumulated Pi (MD = 4.69 mM; 95%CI = 2.79,6.59; p<0.01) more than older muscle during isometric, but not dynamic, contractions. The smaller energetic perturbation in older muscle indicated by these analyses is consistent with its relatively greater use of oxidative energy production. During dynamic contractions, elimination of this greater reliance on oxidative energy production and consequently lower metabolite accumulations in older muscle may be important for understanding task-specific, age-related differences in fatigue.

Comparison of Isometric and Dynamic Bridging Exercises on Low Back Muscle Oxygenation.

Bridging exercises are commonly performed by people with low back pain (LBP). However, the effect of the contraction mode in a bridging exercise on the hemodynamics of the low back muscle has not been investigated in people with and without LBP. The objective of this study was to assess the effect of the mode of bridging exercise on oxygenation of the low back muscle. A near-infrared spectroscopy was used to measure hemodynamic responses of the erector spinae between isometric and dynamic bridging exercises in 16 healthy participants. The results demonstrated that during exercise, the isometric bridging exercise significantly decreased oxyhemoglobin and deoxy-hemoglobin compared to the dynamic bridging exercise (oxyhemoglobin, t=- 3.109, p=0.007, Cohen's d=0.68 and deoxy-hemoglobin, t=- 2.193, P=0.046, Cohen's d=0.60). The results also demonstrated that after exercise, the dynamic bridging exercise induced a significantly higher oxygenation response (oxygenation, t=- 2.178, P=0.048, Cohen's d=0.43). This study indicates that the dynamic bridging exercise is more effective in improving oxygenation of low back muscles.

RhoprCAPA-2 acts as a gonadotropin regulating reproduction in adult female, Rhodnius prolixus

CAPA peptides play diverse roles in insects, modulating muscle contraction, regulating fluid balance, and reproduction. In Rhodnius prolixus, a hematophagous insect and a vector for human Chagas disease, three CAPA peptides are encoded by the capability gene, including RhoprCAPA-1, RhoprCAPA-2, and RhoprCAPA-PK-1. RhoprCAPA-2 is an anti-diuretic hormone in R. prolixus. Here, we explore the involvement of RhoprCAPA-2 in reproduction in adult female R. prolixus. Double-label immunohistochemistry reveals co-localization of RhoprCAPA-2-like and the glycoprotein hormone (GPA2/GPB5) subunit GPB5-like immunoreactivity in neurosecretory cells in the mesothoracic ganglionic mass and in their neurohemal sites, suggesting these peptides can be co-released to regulate physiological processes. qPCR analysis reveals changes in transcript expression levels of the RhoprCAPA receptor (CAPAR) in the fat body and reproductive tissues after feeding in adult female R. prolixus. RNA interference-mediated knockdown of CAPAR transcript decreases egg production and reduces hatching rate and survival rate in female R. prolixus. Downregulation of CAPAR decreases vitellogenin RhoprVg1 transcript expression in the fat body and deceases its receptor RhoprVgR transcript level in the ovaries; accompanied by a reduction in vitellogenin content in the fat body and hemolymph. Incubation of fat body and ovaries in vitro with RhoprCAPA-2 increases RhoprVg1 transcript expression in the fat body, vitellogenin content in the fat body culture medium, and increases RhoprVgR transcript in the ovaries. These findings implicate the CAPA signaling pathway in reproduction, with RhoprCAPA-2 acting as a gonadotropin in adult female R. prolixus.

Eccentric contraction increases hydrogen peroxide levels and alters gene expression through Nox2 in skeletal muscle of male mice.

Hydrogen peroxide (H2O2) is one of the key signaling factors regulating skeletal muscle adaptation to muscle contractions. Eccentric (ECC) and concentric (CONC) contractions drive different muscle adaptations with ECC resulting in greater changes. The present investigation tested the hypothesis that ECC produces higher cytosolic and mitochondrial H2O2 concentrations [H2O2] and alters gene expression more than CONC. Cytosolic and mitochondrial H2O2-sensitive fluorescent proteins, HyPer7 and MLS-HyPer7, were expressed in the anterior tibialis muscle of C57BL6J male mice. Before and for 60 min after either CONC or ECC (100 Hz, 50 contractions), [H2O2]cyto and [H2O2]mito were measured by in vivo fluorescence microscopy. RNA sequencing was performed in control (noncontracted), CONC, and ECC muscles to identify genes impacted by the contractions. [H2O2]cyto immediately after ECC was greater than after CONC (CONC: +6%, ECC: +11% vs. rest, P < 0.05) and remained higher for at least 60 min into recovery. In contrast, the elevation of [H2O2]mito was independent of the contraction modes (time; P < 0.0042, contraction mode; P = 0.4965). The impact of ECC on [H2O2]cyto was abolished by NADPH oxidase 2 (Nox2) inhibition (GSK2795039). Differentially expressed genes were not present after CONC or ECC + GSK but were found after ECC and were enriched for vascular development and apoptosis-related genes, among others. In conclusion, in mouse anterior tibialis, ECC, but not CONC, evokes a pronounced cytosolic H2O2 response, caused by Nox2, that is mechanistically linked to gene expression modifications.NEW & NOTEWORTHY This in vivo model successfully characterized the effects of eccentric (ECC) and concentric (CONC) contractions on cytosolic and mitochondrial [H2O2] in mouse skeletal muscle. Compared with CONC, ECC induced higher and more sustained [H2O2]cyto-an effect that was abolished by Nox2 inhibition. ECC-induced [H2O2]cyto elevations were requisite for altered gene expression.

Functional control of myosin motors in the cardiac cycle.

Contraction of the heart is driven by cyclical interactions between myosin and actin filaments powered by ATP hydrolysis. The modular structure of heart muscle and the organ-level synchrony of the heartbeat ensure tight reciprocal coupling between this myosin ATPase cycle and the macroscopic cardiac cycle. The myosin motors respond to the cyclical activation of the actin and myosin filaments to drive the pressure changes that control the inflow and outflow valves of the heart chambers. Opening and closing of the valves in turn switches the myosin motors between roughly isometric and roughly isotonic contraction modes. Peak filament stress in the heart is much smaller than in fully activated skeletal muscle, although the myosin filaments in the two muscle types have the same number of myosin motors. Calculations indicate that only ~5% of the myosin motors in the heart are needed to generate peak systolic pressure, although many more motors are needed to drive ejection. Tight regulation of the number of active motors is essential for the efficient functioning of the healthy heart - this control is commonly disrupted by gene variants associated with inherited heart disease, and its restoration might be a useful end point in the development of novel therapies.

The investigation of piezoelectric features of lead-free barium titanate ceramic materials at different initial temperatures in the tetragonal phase using molecular dynamics simulation

This study used molecular dynamics simulation to investigate how temperature changes the piezoelectric properties of crystal barium titanate in its tetragonal form. Consistent with the results, the oxygen diffusion coefficient in the simulated sample increased to 0.35 Å2/ns (expansion mode) and 0.56 Å2/ns (contraction mode) by increasing the temperature from 300 to 400 K. Moreover, the piezoelectric coefficient of samples decreased from 267.22 to 162.56 in an expansion mode and from 189.96 to 145.21 in a contraction mode by increasing temperature. On the other hand, increasing the temperature decreased saturation polarization (from 0.372 to 0.290 C/m2), coercivity field (from 0.259 to 0.155 MV/m), and residual polarization (from 0.154 to 0.084). This decrease may be due to approaching the critical temperature and changing the structure from tetragonal to cubic. Finally, the results show that the dielectric coefficients were found by raising the temperatures to 400 K (expansion mode) and getting 73, 70, 68, and 64. For the contraction mode, they were 70, 66, 55, and 63.

Resilience and Flexibility for Clinical Nurses: A Latent Class Analysis

Aim. To explore potential resilience and psychological flexibility patterns in nurses and analyze the effects of related factors such as growth mindset and professional recognition of categories. Background. Resilience and psychological flexibility can help nurses resist occupational pressure and play essential roles in promoting personal growth and professional development. Methods. A latent category approach was used to examine the patterns of heterogeneity in resilience and flexibility among 805 nurses. Differences in the influences related to resilience and flexibility were analyzed using univariate and multivariate logistic regressions, with demographic information, growth mindset, and career recognition as covariates. Results. Participants were divided into three potential categories: toughness-flexible (32.8%), power-deficit-emotional (23.1%), and toughness-rigid (44.1%). The results of multivariate logistic regression analysis showed that monthly income, mode of employment, growth mindset, and professional identity were influential factors in the potential categories of nurse resilience and flexibility. Conclusion. One cohort of nurses had high resilience and low flexibility, and psychological rigidity was related to the fact that the monthly income was less than RMB 5,000 and the contractual mode of employment. An excellent growth mindset and a high professional identity indicate that nurses are resilient and flexible. Implications for Nursing Management. Hospitals and nursing managers should pay attention to nurses’ different career development needs and implement appropriate safeguards.

Does It Matter? Isometric or Isokinetic Assessment of Quadriceps Strength Symmetry 9 Months After ACLR in Collegiate Athletes.

Greater quadriceps strength symmetry is associated with better outcomes after anterior cruciate ligament reconstruction (ACLR). Isometric and isokinetic assessments of quadriceps strength inform therapeutic exercise prescription and return-to-sport decisions. It is unclear whether isometric and isokinetic measures provide similar information post-ACLR. Quadriceps strength symmetry is similar between isometric and isokinetic assessments. Isokinetic and isometric strength symmetries have similar associations to functional knee kinetics and self-reported knee function. Cross-sectional study. Level 3. NCAA Division I athletes (N = 35), 8.9 ± 2.5 months post-ACLR completed isometric and isokinetic quadriceps strength assessments, countermovement jumps (CMJs), and treadmill running. Self-reported knee function was assessed using the International Knee Documentation Committee Subjective Knee Form (IKDC). Agreement between isometric and isokinetic strength symmetry was assessed using Bland-Altman analysis, with associations to functional knee kinetics and IKDC assessed using Pearson correlations and linear regressions. Mean difference in quadriceps strength symmetry between isokinetic and isometric assessments was 1.0% (95% limits of agreement of -25.1% to 23.0%). Functional knee kinetics during running and CMJ were moderately to strongly associated with isometric strength symmetry (r = 0.64-0.80, P < 0.01) and moderately associated with isokinetic strength symmetry (r = 0.41-0.58, P < 0.01). IKDC scores were weakly to moderately associated with isometric (r = 0.39, P = 0.02) and isokinetic (r = 0.49, P < 0.01) strength symmetry. Isokinetic and isometric assessments of quadriceps strength symmetry in collegiate athletes 9 months post-ACLR demonstrated strong agreement. Quadriceps strength symmetry is associated with functional knee kinetic symmetry post-ACLR. Considerable individual variation suggests mode of contraction should be consistent throughout postoperative assessment. Isometric strength symmetry may be a better indicator of functional knee kinetic symmetry, while isokinetic strength symmetry may be associated more closely with patient-reported outcomes.

When royalties impede technology transfer

AbstractWe use data on over 800 early-stage technology transaction negotiations to model the impact of different types of risk on whether the transaction was executed and then test for contractual factors that may ameliorate these risks. Our data highlight the importance of project risk in determining which negotiations result in a signed contract. We find that transactions aiming to sell early-stage technology to large corporates are less likely to be executed when the buyer is large, and the contract contains royalties, holding constant five different types of risk involved in the transaction. Other risk-reducing contract modes do not appear to increase the probability of an executed contract. Our results support the view that technology sellers’ reliance on royalties may reflect organisational preferences or capabilities which may not be economically or managerially optimal. We also find that ‘people risk’ matters more than ‘technological’, ‘market’, ‘appropriation’ and ‘freedom-to-operate’ risks.

Evolutionary Game Analysis on Cooperative Behavior of Major Projects’ Technology Innovation Subjects under General Contracting Mode

Major projects are the important platform for enhancing a country’s comprehensive national power and strengthening its capacity for independent innovation. Although major projects in China have made remarkable achievements, willingness to cooperate and innovate has not achieved the desired target. In this paper, the evolutionary game model of cooperative innovation behavior of general contractors and subcontractors is constructed by considering reputational factors. Through theoretical derivation, the influence of the distribution ratio of collaborative innovation benefit, spillover technology absorption capacity, and reputation discounting coefficient on innovation behavior is analyzed. Finally, MATLAB software is used to simulate the dynamic evolution process of strategy selection. The results show that (1) a reasonable benefit distribution coefficient can promote the evolution of innovation behavior in a positive direction; (2) both the reduction of innovation cost and the increase of spillover technology absorption capacity can make the innovation subject more inclined to choose the active collaborative innovation strategy; and (3) it is the higher-than-threshold reputation loss that can effectively inhibit the “free-rider” behavior. The research conclusions and managerial implications can provide reference for improving the willingness to cooperate in major projects’ technology innovation.

Research on Energy Performance Contracting mode of demand-side reactive power compensation

Demand-side reactive power compensation achieves the purpose of saving energy and protecting the environment by improving the efficiency of electricity consumption and optimizing the way of electricity consumption, reducing electricity consumption and power demand while completing the same power consumption function. However, some users are facing the problems of insufficient funds and immature technical means, and cannot independently carry out demand-side reactive compensation. This paper proposes the demand-side reactive power compensation Energy Performance Contracting model, describes in detail the participants and operation modes in this mode, and uses Shapley value theory to distribute the benefits between the energy-saving service company and the user, and obtains the preliminary revenue distribution scheme. Three factors, namely the proportion of input, risk sharing and negotiating position, were adopted to revise it, and revised again in combination with the degree of implementation contribution to make the distribution of benefits more scientific and reasonable.

Becoming a freelancer or contractor? Drivers’ contractual mode and schedule decisions in a dual sourcing market

In the ride-hailing market, the platforms could recruit contractors subject to prescriptive schedules to reduce the labor supply uncertainty and balance the demand and supply, and the drivers are entitled to become a freelancer or a contractor and choose the schedule they would like to provide the service. This paper proposes an analytical framework to capture the drivers’ decisions of becoming a freelancer and contractor as well as how to arrange their work schedules in a dual sourcing market. The utility structures for two kinds of drivers, freelancers and contractors, are defined and a time-expanded network is adopted to portray the drivers’ work schedule choices. With this setting, the drivers’ simultaneous contractual mode and work schedule selection model is formulated and the algorithm is designed. The numerical examples are conducted to investigate the characteristics of the equilibrium solutions. The results show that a dual-sourcing market is always advantageous to contractors and conditionally beneficial to the platform, freelancers and customers. When there is low potential demand, higher fixed salary is preferred for the platform to attract contractor and complement the labor supply. When the market is thriving, the effect of the profits’ increment by dual-sourcing is not obvious. This work could provide new insights on how to manage a dual-sourcing market for the platform.

Botulinum toxin therapy for management of phantom and residual limb pain following amputation: A systematic review.

Chronic pain following amputation is debilitating. Due to its mechanisms in modulating muscle contraction and pain, botulinum toxin has been investigated as a treatment option for phantom limb pain (PLP) and residual limb pain (RLP). The objective of this study was to determine the efficacy of botulinum toxin injection in the management of PLP and RLP following major limb amputation using a systematic review of the literature. The databases Medline, CINAHL, EMBASE, Scopus, Web of Science, and Cochrane were searched from inception through October 30, 2023. The search identified 50 articles; 37 underwent full-text review, and 11 were included in the final review. Eighty-nine individuals with pain were investigated by the included studies; 53 had RLP and 63 had PLP. There was significant variation in botulinum toxin type, injection method, and dosage. Twenty-one (53.9%) and 27 (64.3%) participants had improvement in PLP and RLP following botulinum toxin injection, respectively. Therefore, there is potential for use of botulinum toxin for the treatment of PLP and RLP. However, due to the minimal number of studies, small sample sizes, and heterogenous methodologies, our ability to conclude with certainty the efficacy of botulinum toxin injection on the treatment of PLP and RLP following amputation is limited.

Resolving an inconsistency in the estimation of the energy for excitation of cardiac muscle contraction.

In the excitation of muscle contraction, calcium ions interact with transmembrane transporters. This process is accompanied by energy consumption and heat liberation. To quantify this activation energy or heat in the heart or cardiac muscle, two non-pharmacological approaches can be used. In one approach using the "pressure-volume area" concept, the same estimate of activation energy is obtained regardless of the mode of contraction (either isovolumic/isometric or ejecting/shortening). In the other approach, an accurate estimate of activation energy is obtained only when the muscle contracts isometrically. If the contraction involves muscle shortening, then an additional component of heat associated with shortening is liberated, over and above that of activation. The present study thus examines the reconcilability of the two approaches by performing experiments on isolated muscles measuring contractile force and heat output. A framework was devised from the experimental data to allow us to replicate several mechanoenergetics results gleaned from the literature. From these replications, we conclude that the choice of initial muscle length (or ventricular volume) underlies the divergence of the two approaches in the estimation of activation energy when the mode of contraction involves shortening (ejection). At low initial muscle lengths, the heat of shortening is relatively small, which can lead to the misconception that activation energy is contraction mode independent. In fact, because cardiac muscle liberates heat of shortening when allowed to shorten, estimation of activation heat must be performed only under isometric (isovolumic) contractions. We thus recommend caution when estimating activation energy using the "pressure-volume area" concept.

Finding relative negative ions concentration in dc glow discharges during undergraduate laboratory work

In this paper, we present a laboratory work implementing a simple method for finding the relative concentration of negative ions in the plasma of a contracted positive column of DC glow discharge. With this method, university students can study processes in gas discharge plasmas in technological gases during their undergraduate laboratory work. The method is based on measuring the positive column radius after the glow discharge transition from a diffuse to a contracted mode. The basics of the physical processes in electronegative plasma and conditions of the positive column contraction are discussed in the paper as well as the practical implementation of the proposed technique. We describe our experimental setup and conditions, and present the experimental data illustrating the method capabilities. Values of the relative concentration of negative ions found with the offered method reasonably agree with other authors’ data obtained by widely accepted diagnostic techniques.

Magnitude and direction of elbow torque asymmetries in manual wheelchair users.

The aims of the present study are to investigate the magnitude and direction of the elbow torque asymmetries in manual wheelchair users and to verify the agreement levels of the asymmetry's direction between different velocities and contraction modes in the isokinetic test. The sample was composed of 14 manual wheelchair users (four women, 10 men). The peak torque of the elbow flexors and extensors were measured on the dominant and non-dominant limbs, using a set of concentric/eccentric contractions at speeds of 60° s-1 and 180° s-1. Asymmetries were calculated by a specific equation, and the levels of agreement of the asymmetry's direction were calculated using Kappa coefficient. The main results showed a large variability in the magnitude of the asymmetries, ranging from -73.1% (ND) to 59.9% (D) between participants. The agreement levels of the elbow flexors and extensors between the different contraction modes were great (k = 0.71-0.85) for most of the velocities [except for flexors of 60° s-1 (k = 0.29)], but the agreement levels were only slight to fair (k = 0.16-0.31) for most of the contraction modes when comparing between velocities [except for flexors eccentric (k = 0.71)]. In conclusion, the elbow torque asymmetries are highly variable between subjects in terms of magnitude. In addition, in general, the limb favored by the asymmetry is the same when comparing between velocities, but not when comparing between contraction modes.

A three‐stage economy optimization method for the aggregator based on electric vehicle user response volumes

AbstractWith the development of intelligent distribution networks and the proposal of the carbon peaking and carbon neutrality goals, the importance of demand‐side management for the improvement of flexible power operation systems is becoming increasingly prominent. To solve the problems of the excessive peak–valley load differences, the insufficient utilization of demand‐side resources, and the unreasonable pricing of aggregators, this paper proposes a three‐stage economy optimization method for the aggregator based on EV(electric vehicle) user response volumes. To gain the advantages of different types of EVs while increasing the dispatchable capacity, the contract mode between the aggregator and EVs is divided into three categories: complete dispatching, rolling reward and punishment mechanism dispatching, and free dispatching. Based on the cloud model, considering loss aversion, the user's own time flexibility, and the impact of the tariff set by the aggregator on the user's decision‐making, we introduced indicator weights to obtain the improved cloud model. Based on the improved cloud model, a user response volume model is obtained. Then, the aggregator performs a three‐stage pricing optimization operation for EVs based on the bid‐winning peak shaving capacity. In the first stage, the attraction between EVs and charging stations is determined based on the law of gravity, and the charging and discharging reward electricity price is set. In the second stage, the dynamic electricity price of three types of EVs and the charging punishment electricity prices of the rolling reward and punishment mechanism dispatching type are determined. In the third stage, the electricity price of the rolling reward and punishment dispatching EVs is further optimized based on their lack of peak shaving capacity. The method proposed in the paper has been verified to be effective in increasing aggregator profits, increasing EV dispatch capacity, and reducing EV charging costs through the example analysis.

Allatotropic peptides modulate muscle contraction of the female reproductive system in Rhodnius prolixus (STÄL)

Allatotropin (AT) acts as a myoregulator at the level of the dorsal vessel (DV) and midgut (MG) in triatominae insects. Previous analyses of the expression of the AT receptor in Rhodnius prolixus showed that AT is expressed in the DV and MG, but also in the reproductive system in females. To further study the activity of AT on female reproductive organs we analyzed the response by adult females in different physiological conditions, including unfed (virgin and mated), and fed mated females (gravid), to doses ranging between 10-14 and 10-6M. Myoregulatory activity was evaluated in vivo, by recording independently the frequency of contractions of each organ after treatment. The results show that the effect of AT varies depending on the organs and on the physiological state of the female. Whilst unfed virgin females did not show response to the peptide for neither of the applied doses, the ovaries showed a differential response, presenting the highest frequency of contractions in gravid individuals. An increase in the frequency of contractions of the oviducts was only observed in mated females. Uterus and spermathecae responded in both gravid and mated females, with maximum activity in the latter. In the bursa, responses were only detected in gravid females. The differential response of the organs seems to be associated to particular moments along the reproductive cycle, such as with the spermathecae that reacted to AT in both unfed mated and gravid females, when the movement of spermatozoids is physiologically crucial. Testes and accessory glands of the male, expressed the mRNA of AT precursor, suggesting that the male would modulate the contractile behavior of the female reproductive system after copula. The ovaries also expressed AT mRNA suggesting the existence of a paracrine/autocrine system modulating muscle contraction.

Contractile and torsional dual-responsive artificial muscles actuated by electric heating and water droplet

Artificial muscle is a kind of soft actuators that can mimic biological muscles to realize contraction, torsion, and other action modes. Since the artificial muscles based on stimuli-responsive materials can drive the robots to achieve bionic motions under different external stimuli, they are expected to be used in various scenarios. Due to high requirements for the component fibrous materials, the artificial muscles capable of responding to two or more forms of stimuli and integrating multiple functions are rarely reported. Although some valuable attempts (host-guest, sheath-core, hybrid spinning methods) have been made to realize multi-responsive and functional artificial muscles, very complicated and demanding preparation processes are usually needed. Here, we used a direct and effective method to develop dual-responsive artificial muscles without excessive requirements on materials: by plying the viscose and silver-coated nylon coiled yarns (in response to water and electric heating, respectively) into double-helix structure, or tying them into single-strand serial structure, the contractile and torsional muscles can be fabricated readily and conveniently. Under concerted or alternate stimulation of water and electric heating, the dual-responsive muscles can exhibit significant performance improvements (in contractile stroke, output force, durability, etc) and achieve new actuation mode (bidirectional torsion) through the interaction and cooperation of the two component yarns. The moisture detectors based on the dual-responsive muscles were also demonstrated. This work provides a feasible way to prepare dual-/multi-responsive muscles using ordinary stimulus-responsive materials. Besides, the multiple stimuli and the interactions between the muscle components can be fully utilized to improve the muscle performances and extend new functions. These methods and concepts will facilitate the development of multi-responsive and functional artificial muscles, and promote their wide applications.

Gravity-efficient motor control is associated with contraction-dependent intracortical inhibition

In humans, moving efficiently along the gravity axis requires shifts in muscular contraction modes. Raising the arm up involves shortening contractions of arm flexors, whereas the reverse movement can rely on lengthening contractions with the help of gravity. Although this control mode is universal, the neuromuscular mechanisms that drive gravity-oriented movements remain unknown. Here, we designed neurophysiological experiments that aimed to track the modulations of cortical, spinal, and muscular outputs of arm flexors during vertical movements with specific kinematics (i.e., optimal motor commands). We report a specific drop of corticospinal excitability during lengthening versus shortening contractions, with an increase of intracortical inhibition and no change in spinal motoneuron responsiveness. We discuss these contraction-dependent modulations of the supraspinal motor output in the light of feedforward mechanisms that may support gravity-tuned motor control. Generally, these results shed a new perspective on the neural policy that optimizes movement control along the gravity axis.