Force Relaxation Research Articles

Ablation of skeletal muscle estrogen receptor alpha impairs contractility in male mice.

Estradiol and estrogen receptor α (ERα) have been shown to be important for the maintenance of skeletal muscle strength in females; however, little is known about the roles of estradiol and ERα in male muscle. The purpose of this study was to determine if skeletal muscle ERα is required for optimal contractility in male mice. We hypothesize that reduced ERα in skeletal muscle impairs contractility in male mice. Skeletal muscle-specific knockout (skmERαKO) male mice exhibited reduced strength across multiple muscles and several contractile parameters related to force generation and kinetics compared with wild-type littermates (skmERαWT). Isolated EDL muscle-specific isometric tetanic force, peak twitch force, peak concentric and peak eccentric forces, as well as the maximal rates of force development and relaxation were 11%-21% lower in skmERαKO compared with skmERαWT mice. In contrast, isolated soleus muscles from skmERαKO mice were not affected. In vivo peak torque of the anterior crural muscles was 20% lower in skmERαKO compared with skmERαWT mice. Muscle masses, contractile protein contents, fiber types, phosphorylation of the myosin regulatory light chain, and caffeine-elicited force did not differ between muscles of skmERαKO and skmERαWT mice, suggesting that strength deficits were not due to size, composition, or calcium release components of muscle contraction. These results indicate that in male mice, reduced skeletal muscle ERα blunts contractility to a magnitude similar to that previously reported in females; however, the mechanism may be sexually dimorphic.NEW & NOTEWORTHY We comprehensively measured in vitro and in vivo contractility of leg muscles with reduced estrogen receptor α (ERα) in male mice and reported that force generation and contraction kinetics are impaired. In contrast to findings in females, phosphorylation of myosin regulatory light chain cannot account for low force production in male skeletal muscle ERα knockout mice. These results indicate that ERα is required for optimal contractility in males and females but via sexually dimorphic means.

Viscoelastic phenotyping of red blood cells

Red blood cells (RBCs) are the simplest cell types with complex dynamical and viscoelastic phenomenology. While the mechanical rigidity and the flickering noise of RBCs have been extensively investigated, an accurate determination of the constitutive equations of the relaxational kinetics is lacking. Here we measure the force relaxation of RBCs under different types of tensional and compressive extension-jump protocols by attaching an optically trapped bead to the RBC membrane. Relaxational kinetics follows linear response from 60 pN (tensional) to −20 pN (compressive) applied forces, exhibiting a triple exponential function with three well-separated timescales over four decades (0.01–100 s). While the fast timescale (τF∼0.02(1)s) corresponds to the relaxation of the membrane, the intermediate and slow timescales (τI=4(1)s; τS=70(8)s) likely arise from the cortex dynamics and the cytosol viscosity. Relaxation is highly heterogeneous across the RBC population, yet the three relaxation times are correlated, showing dynamical scaling. Finally, we find that glucose depletion and laser illumination of RBCs lead to faster triple exponential kinetics and RBC rigidification. Viscoelastic phenotyping is a promising dynamical biomarker applicable to other cell types and active systems.

Analysis of frictionless contact between a spherical indenter and a poroviscoelastic medium with a constant contact radius

The research aims to understand the force relaxation that occurs when a spherical indenter is pressed into poroviscoelastic materials, which exhibit viscoelastic properties of solid network and drainage behavior of infiltrated fluid. To achieve this, an analytical approach is proposed to model spherical indentation on a poroviscoelastic medium under the condition of a constant contact radius. This analysis is conducted in the Laplace-transformed domain, and provides closed-form expressions in the transformed domain for both the normal approach and the contact force of the indenter while maintaining a fixed contact radius. These expressions are then numerically inverse-transformed to the time domain for practical analysis. To account for different scenarios, we consider various combinations of drainage conditions at the top and smoothness conditions at the bottom of the medium. We examine three categories of viscoelastic solid behavior, as understanding how they respond under indentation is crucial for characterizing their mechanical behavior. Additionally, we conduct finite element simulations of spherical indentation on poroviscoelastic media, serving as a comparison to the semi-analytic results obtained. Notably, the thickness of the medium relative to the contact radius and the Poisson's ratio play significant roles in the evolution of both the normal approach and contact force of the spherical indenter over time.

Force relaxation response in the poroelastic axisymmetric Boussinesq problem for an indenter of arbitrary profiles I: Permeable and impermeable surface drainage conditions

In this study, we have derived a theoretical solution for the poroelastic axisymmetric Boussinesq problem when an indenter with arbitrary profiles is subjected to step displacement loading. The analysis is conducted within the framework of Biot’s theory, employing the McNamee–Gibson displacement function method. We explore two distinct scenarios for surface drainage boundary conditions: one where the surface allows full permeability and another where it is fully impermeable. The formulation of the mechanical boundary condition at the surface relies on an equation that establishes the relationship between the depth of indentation and the contact radius. Our solution encompasses two aspects: force asymptotes at the undrained and drained limits, and a normalized force relaxation that accounts for transient responses. Specific findings are presented for three indenter shapes: paraboloidal, conical, and cylindrical. Of particular significance, we demonstrate that for these specific indenter shapes, the normalized force relaxation at ω=0 can be expressed in closed form in the Laplace domain. In addition to this analytical breakthrough, we conducted numerical simulations employing actual indenters. Remarkably, the normalized force relaxation curves from actual indenters show negligible dependence on material properties and closely align with our closed-form solution at ω=0. This finding suggests that the closed-form solution could act as a universal master curve capable of characterizing the normalized force relaxation response in instances of a real indenter, irrespective of material properties.

Enhancement of neural crest formation by mechanical force in Xenopus development.

In vertebrate development, ectoderm is specified into neural plate (NP), neural plate border (NPB), and epidermis. Although such patterning is thought to be achieved by molecular concentration gradients, it has been revealed, mainly by in vitro analysis, that mechanical force can regulate cell specification. During in vivo patterning, cells deform and migrate, and this applies force to surrounding tissues, shaping the embryo. However, the role of mechanical force for cell specification in vivo is largely unknown. In this study, with an aspiration assay and atomic force microscopy, we have demonstrated that tension on ectodermal cells decreases laterally from the midline in Xenopus early neurula. Ectopically applied force laterally expanded the neural crest (NC) region, a derivative of the NPB, whereas force relaxation suppressed it. Furthermore, force application activated both the FGF and Wnt pathways, which are required for NC formation during neuroectodermal patterning. Taken together, mechanical force is necessary for NC formation in order to regulate signaling pathways. Furthermore, molecular signals specify the NP and generate force on neighboring tissue, the NPB, with its closure. This force activates signals, possibly determining the appropriate width of a narrow tissue, the NC.

Door Opening and Closing Considering Forces Using a Mobile Manipulator with an Admittance Controlled Arm

This study achieved four door operations, namely push-opening, push-closing, pull-opening, and pull-closing movements, using a mobile manipulator consisting of a commercially available arm robot and a mobile robot. We assumed that the arm robot is controlled by position commands at intervals of a few milliseconds, and that the mobile robot is guided by a simple straightforward linear trajectory. Ott, Borst, Bäuml, and Hirzinger proposed a push-opening method using impedance control in a cylindrical coordinate system for the arm robot. With this control, when the mobile robot advances toward and through the door, the arm robot moves passively and properly pushes the door open. However, their method is unsuitable for the above type of robot. Thus, we propose a method with two modifications: the use of admittance control and the improvement of force relaxation by considering a force obtained through a novel force decomposition. Furthermore, the proposed method was demonstrated not only in the push-opening movement but also in the push-closing, pull-opening, and pull-closing movements.

FMRI changes during multi-limb movements in Parkinson's disease.

BackgroundWhile motor coordination problems are frequently reported among individuals with Parkinson’s disease (PD), the effects of the disease on the performance of multi-limb movements and the brain changes underlying impaired coordination are not well-documented.ObjectiveFunctional magnetic resonance imaging (fMRI) was used to examine differences in brain activity during a task that involved the coordination of non-homologous limbs (i.e., ipsilateral hand and foot) in individuals with and without PD.MethodsParticipants included 20 PD and 20 healthy control participants (HC). They were instructed to generate force in a coordinated manner by simultaneously contracting their ipsilateral hand and foot. PD were tested off their antiparkinsonian medication and on their more affected side, whereas the side in controls was randomized.ResultsAlthough both groups were able to coordinate the two limbs to produce the expected level of force, PD had a slower rate of force production and relaxation compared to HC. Additionally, their globus pallidus and primary motor cortex were underactive, whereas their pre-supplementary motor area (pre-SMA) and lateral cerebellum were overactive relative to HC. Importantly, in PD, the fMRI activity within the pre-SMA correlated with the rate of force decrease.ConclusionMulti-limb force control deficits in PD appear to be related to widespread underactivation within the basal ganglia-cortical loop. An overactivation of higher-level motor regions within the prefrontal cortex and lateral cerebellum may reflect increased cognitive control and performance monitoring that emerges during more complex motor tasks such as those that involve the coordination of multiple limbs.

Neuromechanical characterization of the abductor hallucis and its potential role in upright postural control.

There is growing evidence to support a role for the abductor hallucis (AH) in standing balance control; however, functional properties of the muscle that may provide more insight into AH's specific contribution to upright posture have yet to be characterized. This study was conducted to quantify functional neuromechanical properties of the AH and correlate the measures with standing balance variables. We quantified strength and voluntary activation during maximal voluntary isometric contractions of the great toe abductor in nine (3 females and 6 males) healthy, young participants. During electrically evoked twitch and tetanic contractions, we measured great toe abduction peak force and constructed a force-frequency curve. We also evaluated peak abduction force, contraction time (CT), half-relaxation time (HRT), rate of force development (RFD), and relaxation rate (RR) from twitch contractions evoked using doublet stimuli. Strength, VA, CT, HRT, RFD, and RR were correlated to centre of pressure standard deviation (COP SD) and velocity (COP VEL) variables of the traditional COP trace and its rambling and trembling components during single-legged stance. AH twitch properties (e.g., CT: 169.8±32.3ms; HRT: 124.1±29.2ms) and force-frequency curve were similar to other slow contractile muscles. Contractile speed related negatively with COP VEL, suggesting AH may be appropriate for slow, prolonged tasks such as ongoing postural balance control. Correlation coefficient outcomes for all variables were similar between rambling and trembling components. Our results provide further evidence for the importance of AH neuromechanical function for standing balance control, at least during a challenging single-legged posture.

A compatible uniaxial Bouc–Wen model for accurate estimation of residual deformation of seismically isolated structures

Bouc–Wen (BW) model is commonly used to model lead rubber bearings (LRBs) in seismically isolated buildings. However, the original BW model violates the Drucker’s or Ilyushin’s postulate of plasticity by displaying the displacement drift, force relaxation, and non-closure of hysteretic loops. These deficiencies can significantly impact the seismic performance of the isolated structures, leading to unrealistic evaluation of residual deformation concentrated in the isolation layer. To address these issues, a step-by-step amendment algorithm is proposed to develop a compatible uniaxial BW (CBW) model that conforms to the basic physical rules. The proposed algorithm involves adding a reinforcement factor to the short-path reloading branches, defining reversal and reloading points to identify reloading behavior. Furthermore, it develops an adaptive limit to distinguish between the short-path and full-path reloading branches. The proposed algorithm was validated using various short unloading–reloading scenarios. Subsequently, a simplified single degree of freedom (SDOF) model representing a seismically isolated building was defined. Incremental dynamic analysis was performed to evaluate the seismic responses of the isolated building designed with the original BW, CBW, and bilinear models. Results indicate that although the peak displacement and seismic force of the isolation layer induced by the three models produce small deviations, considerable errors in residual displacement are observed. Compared with the original BW model, the bilinear model produces unrealistic sharp yielding transition and overestimates the residual displacement. However, it can reduce displacement drift and force relaxation. By contrast, the proposed CBW with the improved algorithm can effectively correct the defects of the original BW and bilinear models. The CBW model can be used to accurately estimate the residual deformation of the seismically isolated buildings.

Effect of force adjustment modalities on characteristics for force generation and relaxation

BACKGROUND: The systematic characteristics of force generation and relaxation have been investigated using a graded isometric task for several target levels and magnitudes in the upper and lower limb. However, whether a relaxation modality affects the accuracy or speed of grading remains unclear. In addition, speed characteristics are still unclear in both force generation and relaxation modalities. OBJECTIVE: To investigate the effect of force adjustment modalities on force generation and relaxation characteristics. METHODS: Participants were instructed to match a target force level as quickly and as accurately as possible under peak and keep adjustment modalities. The force generation task was increased from 10% to 30%, 50%, and 70% of the maximum voluntary force (MVF). The force relaxation task was decreased from 70% to 50%, 30%, and 10% MVF. The recorded force was analyzed. Errors in reproduction were computed in both modalities and target levels of force. RESULTS: The errors of the peak adjustment modality were greater than those of the keep adjustment modality in both tasks. The reaction time was longer with the peak adjustment modality than with the keep adjustment modality in both tasks. CONCLUSION: Speed was affected by the choice of adjustment modality.

Effect of the Novel Myotrope Danicamtiv on Cross-Bridge Behavior in Human Myocardium.

Background Omecamtiv mecarbil (OM) and danicamtiv both increase myocardial force output by selectively activating myosin within the cardiac sarcomere. Enhanced force generation is presumably due to an increase in the total number of myosin heads bound to the actin filament; however, detailed comparisons of the molecular mechanisms of OM and danicamtiv are lacking. Methods and Results The effect of OM and danicamtiv on Ca2+ sensitivity of force generation was analyzed by exposing chemically skinned myocardial samples to a series of increasing Ca2+ solutions. The results showed that OM significantly increased Ca2+ sensitivity of force generation, whereas danicamtiv showed similar Ca2+ sensitivity of force generation to untreated preparations. A direct comparison of OM and danicamtiv on dynamic cross-bridge behavior was performed at a concentration that produced a similar force increase when normalized to predrug levels at submaximal force (pCa 6.1). Both OM and danicamtiv-treated groups slowed the rates of cross-bridge detachment from the strongly bound state and cross-bridge recruitment into the force-producing state. Notably, the significant OM-induced prolongation in the time to reach force relaxation and subsequent commencement of force generation following rapid stretch was dramatically reduced in danicamtiv-treated myocardium. Conclusions This is the first study to directly compare the effects of OM and danicamtiv on cross-bridge kinetics. At a similar level of force enhancement, danicamtiv had a less pronounced effect on the slowing of cross-bridge kinetics and, therefore, may provide a similar improvement in systolic function as OM without excessively prolonging systolic ejection time and slowing cardiac relaxation facilitating diastolic filling at the whole-organ level.

High stretching tuned GO decorated non-shrinkable polyacrylic acid-based composite fiber and its excellent performance as a Fenton catalyst

Mixed valent iron ions were used to create a flexible ionic crosslinking network through coordination, making PAA fiber highly stretchable, and the fiber was highly stretched to tear graphene oxide (GO) sheets into discontinuously-dispersed monolayer sheets. The monolayer sheets could construct many hydrogen bonds with PAA chains to serve as knots to hinder chain movement, controlling the shrinkage of stretched fiber. Co-solvent formamide could improve the heat resistance of PAA fiber through special calorific effect; thus the highly-stretched fiber could tolerate high temperature heat setting. Due to the advanced structure induced by stretching, internal force relaxation caused by heat setting, and the existence of knots, the resulting fiber possessed the features of high strength and no shrinkage. High strength made the fiber mechanically applicable, and the unshrinkability could help it to maintain large specific surface area and strong iron ions-immobilizing capability. As a result, the catalytic activity of non-shrinkable fiber was increased by 25% compared with that of shrinkable fiber for methylene blue (MB) decolorization, and iron ion loading ratio was increased by 174.5%; however, iron ion leaching ratio was decreased by 76.5%, which was conducive to reusability improvement. Thereby, the resulting fiber could be repeatedly used to decolorize MB.

The rate of force relaxation scaling factor is highly sensitive to detect upper and lower extremity motor deficiencies in mildly affected people with multiple sclerosis.

The motor symptoms affecting upper and lower extremity functioning in people with multiple sclerosis (PwMS) are considered the cardinal symptoms of multiple sclerosis. There is still a need for outcome measures that can sensitively evaluate these symptoms. We aimed to investigate the sensitivity of the isometric outcomes (maximum force; Fmax, maximum rate of force development; RFDmax, rate of force development scaling factor; RFD-SF, and rate of force relaxation scaling factor; RFR-SF) and standard clinical tests (9-hole peg test; 9HPT and timed 25-feet walk test; T25FW) in detecting the upper and lower extremity motor deficiencies in PwMS and also in a subgroup of mildly affected PwMS whose performance in standard clinical tests were similar to controls. Twenty-nine PwMS (age: 47.9 (8.6) years, relapsing-remitting type, expanded disability status scale: 2.5 (1.5)) and their age- and gender-matched controls completed an identical testing protocol in the upper (grip force muscles) and lower (knee extensors) extremities. For each extremity, we assessed Fmax, RFDmax, RFD-SF, and RFR-SF. Additionally, participants completed standard clinical tests for the evaluation of upper- (9HPT) and lower-extremity (T25FW) function. Comparisons were made between controls and PwMS 1) using all study participants and 2) including only mildly affected PwMS whose performance in standard functional tests was comparable to controls. Independent sample t-tests were utilized to compare groups, with a p-value set at 0.01 to correct for multiple comparisons. P-values and effect sizes were used to evaluate the sensitivity of the outcome measures in detecting group differences. Our results indicate that most isometric outcomes and standard functional tests were sensitive in detecting motor deficiencies in both upper and lower extremities between groups (p<0.001). Among participants, 16 PwMS in 9HPT and 11 PwMS in T25FW demonstrated performance similar to that of the control group (9HPT: 18.85 (2.20) s vs 17.81 (2.19) s; p=0.19) and (T25FW: 3.60 (0.42) s vs 3.58 (0.29) s; p=0.92). The results of the comparisons between mildly affected PwMS and their controls indicate that RFR-SF is the only sensitive isometric outcome to detect differences between groups in the upper (-8.24 (0.76) 1/s vs -8.93 (0.6) 1/s; p=0.008) and lower extremity (-5.86 (1.13) 1/s vs -7.71 (1.11) 1/s; p<0.001). The rate of force relaxation scaling factor, which assesses the ability to rapidly relax muscle forces after quick contractions, demonstrates high sensitivity in detecting motor deficiencies in PwMS, even when the current standard clinical outcomes fail to detect these differences. Our findings emphasize the importance of future randomized controlled trials focusing on rehabilitative and therapeutic interventions that specifically target muscle force relaxation to enhance motor functioning in PwMS.

Grip Rate Of Force Relaxation Is Associated With Muscle Endurance In Older Adults

Grip Rate Of Force Relaxation Is Associated With Muscle Endurance In Older Adults

Abstract P2008.1: Association Of Myocardial Stiffening With Impaired Relaxation In A Diabetic Murine Model Of Left Ventricular Diastolic Dysfunction

Introduction: Left ventricular diastolic dysfunction (LVDD) is often manifested by impaired relaxation and myocardial stiffening in the left ventricle (LV). While impairments in the function of myofilament regulatory proteins are known to deteriorate LV relaxation, the effects of passive myocardial stiffening on the relaxation of active forces remain unknown. Methods: A diabetic murine model of LVDD (db/db, n=5) and wild-type mice (WT, n=5) were used to study the association between tissue-level passive stiffness and organ-level relaxation. Early transmitral flow velocity to mitral annular tissue velocity ratio (E/e’), measured by Doppler imaging, was used to assess LV relaxation. Cardiac magnetic resonance imaging was performed using a 7T Bruker scanner to estimate diastolic strains via image registration. Mechanical testing was performed on harvested LV free wall (LVFW) specimens to measure passive stiffness. Results: LVDD was confirmed by a high septal E/e’ ratio (Fig. 1A). The db/db mice presented an increase in passive LVFW stiffness measured as the tangent to the circumferential stress-strain curve at 30% strain (Fig. 1B). A positive correlation was observed between passive stiffness and E/e’ (Fig. 1C). End-diastolic strain calculations (Fig. 1D) corroborated LV filling impairment indicating significant reductions in circumferential LV strains (Fig. 1E). Conclusion: Passive stiffening may impair LV filling by not only restraining the passive stretch of the myocardium at diastole but also by decelerating the active relaxation. Further integrated in-vivo and ex-vivo studies of LVDD can deconvolute the “active” and “passive” causes of impaired relaxation.

Voluntary wheel running and lithium supplementation improves muscle force production without altering SERCA function in the D2 mdx mouse

Background: Duchenne muscular dystrophy (DMD) is an X-linked recessive muscle wasting disease that, with no cure, leads to early mortality (30-40 years of age). Previous studies have shown that voluntary wheel running can mitigate disease pathology and improve muscle contractility in the preclinical mdx mouse model. We have shown that treating wild-type (WT) mice with a low dose of lithium, a natural inhibitor of glycogen synthase kinase 3, enhanced soleus (SOL) and extensor digitorum longus (EDL) muscle contractility. Our objectives were to test our hypothesis of whether combining VWR with low dose lithium supplementation could provide further benefits to muscle contractility in DBA/2J mdx mice – a model that displays far worse disease severity compared with the traditional C57BL/10 mdx mouse. We also examined if this combined intervention could improve muscle calcium regulation in muscle by assessing sarco(endo)plasmic reticulum Ca 2+ -ATPase (SERCA) function as we have recently shown that SERCA function is drastically impaired in D2 mdx mice, which could also contribute to deficits in muscle force production. Methods: Young (5-6 week old) male D2 WT and mdx mice were ordered from Jackson Laboratory. D2 mdx mice were assigned into each of the following conditions: sedentary ( mdxSED), voluntary wheel running ( mdxVWR), or VWR+lithium chloride ( mdxVWR+Li). The VWR groups were given access to a cagewheel for a total of 6 weeks, and the mdxVWR+Li group were provided a low dose of LiCl (50 mg/kg/day) via drinking water for the entire duration of the study. After 6 weeks, all mice were euthanized and the SOL and EDL muscles were subjected to force-frequency curve analysis (1-160 Hz). SERCA function was assessed by performing SERCA activity assays and a Ca 2+ uptake assay. Results: In the SOL, the combined effect of lithium and VWR improved specific force production to near WT levels across submaximal and maximal frequencies. Specific force production in the mdxVWR+Li group was significantly greater compared to the mdxSED group at all stimulation frequencies. Rate of SOL force development was significantly lower in all mdx groups compared to WT. However, rate of relaxation was only significantly reduced (vs. WT) within the mdxSED group, suggesting that VWR and VWR+Li improved relaxation. This could not be explained by any changes in SERCA function. In the EDL, specific force was significantly (p&lt;0.001) reduced across mdx groups compared to WT; however, of all mdx groups, the mdxVWR+Li produced the most force and was significantly different compared to mdxVWR at 80 and 160 Hz. Rates of force development and relaxation were all slower in all mdx groups compared to WT, and there were no differences in SERCA activity. Conclusions: Combining lithium supplementation with VWR improved SOL and EDL force production in the D2 mdx mouse without any changes to SERCA function. V.A.F is a Tier 2 Canada Research Chair in Muscle Plasticity and Tissue-Remodelling. 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.

Demographic Factors and Their Impact on the Development of Pension System in Russia

The development of the state pension system of the Russian Federation is accomplished within the frames of Strategy-2030 and oriented towards attaining national goals and UN Targets of Sustainable Development. According to requirements of strategic documents parameters of the pension system shall be connected with basic macroeconomic and demographic indicators that can both stimulate and restrict its development. As the pension system is fully integrated in the national finance system, its functioning depends directly on finance relations between participants (employees, employers, the Pension Fund of Russia (PFR) and federal budget). However, demographic factors, such as life-span, gender structure, dynamics of birth and death, etc. act as a limiter of finance relations. The article studies changes in demographic factors and finds the trend of population aging, which could have an adverse effect on pensions of Russian citizens. Irrespective of organizational structure of the pension system and amalgamation of two biggest non-budget funds demographic problem is still an important component that affects pension provision. After-effects of the pandemic, forced relaxation and growing life expectancy of the population decreases the gap between the number of working population and the number of pensioners (coefficient of age dependence), which can result in the necessity to look for additional stimulus to the development of the pension system and raising welfare of pensioners. The goal of the article is to substantiate the trend of demographic aging of the population, which leads to higher load on the pension system.

Experimental study on forming mechanism and mechanical properties of novel self-tightening one-side bolt

In the connection of steel structures, the traditional torshear type high-strength bolt needs two operating planes, which is difficult to be applied to the connection between members with closed sections. Given the problem, a new type of professional self-tightening high-strength one-side bolt (SHSOB-PRO) was developed based on the existing SHSOB (Self-tightening High-Strength One-side Bolt). Three experiments were carried out. For the anchor end forming mechanism test, the influences of the parameters including the deformation guiding mechanisms, deformation sleeve materials, and processing technology were analyzed. For the internal force release mechanism test of the outer sleeve, the release process of the internal force of the outer sleeve was revealed, and the release mechanism of the clamping teeth-shear bearing washer was proposed. For the final forming test, the complete forming process of SHSOB-PRO was given. In addition, a series of tests on the mechanical properties were conducted, including pre-tightening force relaxation tests, tensile capacity tests, and shear behavior tests. The mechanical properties of SHSOB-PRO, including shear resistance and tensile resistance were investigated. Calculation formulas of shear capacity were given. The results illustrated that the form of the anchor end of SHSOB-PRO was stable; the pre-tightening force loss laws of SHSOB-PRO and traditional M20 torshear type high strength bolts were similar, the pre-tightening force level was slightly higher than that of the same batch of traditional torshear type bolts. The tensile capacity, and the shear capacity of SHSOB-PRO met the requirements of current Chinese specifications, indicating that the SHSOB-PRO can be applied in engineering.

Rate control deficits during pinch grip and ankle dorsiflexion in early-stage Parkinson's disease.

Much of our understanding of the deficits in force control in Parkinson's disease (PD) relies on findings in the upper extremity. Currently, there is a paucity of data pertaining to the effect of PD on lower limb force control. The purpose of this study was to concurrently evaluate upper- and lower-limb force control in early-stage PD and a group of age- and gender-matched healthy controls. Twenty individuals with PD and twenty-one healthy older adults participated in this study. Participants performed two visually guided, submaximal (15% of maximum voluntary contractions) isometric force tasks: a pinch grip task and an ankle dorsiflexion task. PD were tested on their more affected side and after overnight withdrawal from antiparkinsonian medication. The tested side in controls was randomized. Differences in force control capacity were assessed by manipulating speed-based and variability-based task parameters. Compared with controls, PD demonstrated slower rates of force development and force relaxation during the foot task, and a slower rate of relaxation during the hand task. Force variability was similar across groups but greater in the foot than in the hand in both PD and controls. Lower limb rate control deficits were greater in PD with more severe symptoms based on the Hoehn and Yahr stage. Together, these results provide quantitative evidence of an impaired capacity in PD to produce submaximal and rapid force across multiple effectors. Moreover, results suggest that force control deficits in the lower limb may become more severe with disease progression.

Methodologies and models for measuring viscoelastic properties of cancer cells: Towards a universal classification

Different methods and several physical models exist to study cell viscoelasticity with the atomic force microscope (AFM). In search of a robust mechanical classification of cells through AFM, in this work, viscoelastic parameters of the cancer cell lines MDA-MB-231, DU-145, and MG-63 are obtained using two methodologies; through force–distance and force–relaxation curves. Four mechanical models were applied to fit the curves. The results show that both methodologies agree qualitatively on the parameters that quantify elasticity but disagree on the parameters that account for energy dissipation. The Fractional Zener (FZ) model represents well the information given by the Solid Linear Standard and Generalized Maxwell models. The Fractional Kelvin (FK) model concentrates the viscoelastic information mainly in two parameters, which could be an advantage over the other models. Therefore, the FZ and FK models are proposed as the basis for the classification of cancer cells. However, more research using these models is needed to obtain a broader view of the meaning of each parameter and to be able to establish a relationship between the parameters and the cellular components.