Why muscle is an efficient shock absorber

Quadriceps recovery and pain relief in knee osteoarthritis rats by cog polydioxanone filament insertion

Quadriceps muscles play a pivotal role in knee osteoarthritis (OA) progression and symptom manifestation, particularly pain. This research investigates the therapeutic effectiveness of muscle enhancement and support therapy (MEST), a recently developed device intended for intramuscular insertion of cog polydioxanone filaments, in quadriceps restoration to alleviate OA pain. Knee OA was induced in Sprague Dawley rats via monoiodoacetate injections. MEST or sham treatment was performed in OA or Naive rat quadriceps. Pain was assessed using paw withdrawal threshold and weight bearing. Quadriceps injury and recovery via MEST were evaluated using biomarkers, tissue morphology, muscle mass, contractile force and hindlimb torque. Satellite cell and macrophage activation, along with their activators, were also assessed. Data were compared at 1- and 3-weeks post-MEST treatment (M-W1 and M-W3). MEST treatment in OA rats caused muscle injury, indicated by elevated serum aspartate transferase and creatinine kinase levels, and local β-actin changes at M-W1. This injury triggered pro-inflammatory macrophage and satellite cell activation, accompanied by heightened interleukin-6 and insulin-like growth factor-1 levels. However, by M-W3, these processes gradually shifted toward inflammation resolution and muscle restoration. This was seen in anti-inflammatory macrophage phenotypes, sustained satellite cell activation and injury markers regressing to baseline. Quadriceps recovery in mass and strength from atrophy correlated with substantial OA pain reduction at M-W3. This study suggests that MEST-induced minor muscle injury triggers macrophage and satellite cell activation, leading to recovery of atrophied quadriceps and pain relief in OA rats.

Alleviation of peripheral sensitization by quadriceps insertion of cog polydioxanone filaments in knee osteoarthritis rats

A recently established therapeutic strategy, involving the insertion of biodegradable cog polydioxanone filaments into the quadriceps muscles using the Muscle Enhancement and Support Therapy (MEST) device, has demonstrated significant efficacy in alleviating knee osteoarthritis (OA) pain. This study investigated changes in peripheral sensitization as the potential mechanism underlying MEST-induced pain relief in monoiodoacetate (MIA) induced OA rats. The results revealed that MEST treatment potently reduces MIA-induced sensitization of L3/L4 dorsal root ganglion (DRG) neurons, the primary nociceptor pathway for the knee joint. This reduction in DRG sensitization, as elucidated by voltage-sensitive dye imaging, is accompanied by a diminished overexpression of TRPA1 and NaV1.7, key nociceptor receptors involved in mechanical pain perception. Importantly, these observed alterations strongly correlate with a decrease in mechanically-evoked pain behaviors, providing compelling neurophysiological evidence that MEST treatment alleviates OA pain by suppressing peripheral sensitization.

Strength Training vs. Aerobic Training for Managing Pain and Physical Function in Patients with Knee Osteoarthritis: A Systematic Review and Meta-Analysis

(1) Background: Strength training (ST) and aerobic training (AT) are the most recommended interventions in patients with knee OA. These recommendations are supported by high-quality evidence, but it is still unknow whether one type of exercise is superior to the other. Thus, the aim was to investigate whether one type of exercise (ST or AT) is superior to the other for improving pain and physical function in patients with knee osteoarthritis. (2) Methods: A systematic review and meta-analysis was carried out following the PRISMA statement. The search strategy was conducted in PubMed, PEDro, Scopus, Web of Science and Cochrane Library databases. Randomized controlled trials comparing ST and AT on pain intensity and physical function in patients with knee osteoarthritis were included. Methodological quality and risk of bias were assessed with a PEDro scale and risk-of-bias tool, respectively. The certainty of evidence was evaluated using GRADE guidelines. (3) Results: Four studies (6 publications) were included. The qualitative and quantitative synthesis showed that ST produces no more improvement in pain intensity (SMD after intervention: 0.02; 95%CI: -0.15, 0.19; I2: 0%; three studies; 426 patients) and physical function (SMD after intervention: 0.07; 95%CI: -0.10, 0.24; I2: 0%; three studies; 426 patients) compared to AT in patients with knee osteoarthritis. The certainty of evidence was rated as very low. (4) Conclusions: Both type of exercises showed clinical benefits in people with knee osteoarthritis, but no differences between ST and AT were found.

Electrically active smart adhesive for a perching-and-takeoff robot

Perching-and-takeoff robot can effectively economize onboard power and achieve long endurance. However, dynamic perching on moving targets for a perching-and-takeoff robot is still challenging due to less autonomy to dynamically land, tremendous impact during landing, and weak contact adaptability to perching surfaces. Here, a self-sensing, impact-resistant, and contact-adaptable perching-and-takeoff robot based on all-in-one electrically active smart adhesives is proposed to reversibly perch on moving/static dry/wet surfaces and economize onboard energy. Thereinto, attachment structures with discrete pillars have contact adaptability on different dry/wet surfaces, stable adhesion, and anti-rebound; sandwich-like artificial muscles lower weight, enhance damping, simplify control, and achieve fast adhesion switching (on-off ratio approaching ∞ in several seconds); and the flexible pressure (0.204% per kilopascal)-and-deformation (force resolution, <2.5 millinewton) sensor enables the robot's autonomy. Thus, the perching-and-takeoff robot equipped with electrically active smart adhesives exhibits tremendous advantages of soft materials over their rigid counterparts and promising application prospect of dynamic perching on moving targets.

Topological damping in an ultrafast giant cell

Cellular systems are known to exhibit some of the fastest movements in biology, but little is known as to how single cells can dissipate this energy rapidly and adapt to such large accelerations without disrupting internal architecture. To address this, we investigate Spirostomum ambiguum-a giant cell (1-4 mm in length) well-known to exhibit ultrafast contractions (50% of body length) within 5 ms with a peak acceleration of 15[Formula: see text]. Utilizing transmitted electron microscopy and confocal imaging, we identify an association of rough endoplasmic reticulum (RER) and vacuoles throughout the cell-forming a contiguous fenestrated membrane architecture that topologically entangles these two organelles. A nearly uniform interorganelle spacing of 60 nm is observed between RER and vacuoles, closely packing the entire cell. Inspired by the entangled organelle structure, we study the mechanical properties of entangled deformable particles using a vertex-based model, with all simulation parameters matching 10 dimensionless numbers to ensure dynamic similarity. We demonstrate how entangled deformable particles respond to external loads by an increased viscosity against squeezing and help preserve spatial relationships. Because this enhanced damping arises from the entanglement of two networks incurring a strain-induced jamming transition at subcritical volume fractions, which is demonstrated through the spatial correlation of velocity direction, we term this phenomenon "topological damping." Our findings suggest a mechanical role of RER-vacuolar meshwork as a metamaterial capable of damping an ultrafast contraction event.

Effects of a foot-ankle muscle strengthening program on pain and function in individuals with knee osteoarthritis: a randomized controlled trial

BACKGROUND

Foot-ankle exercises could improve pain and function of individuals with KOA and need to be tested.

OBJECTIVE

To investigate whether an 8-week foot-ankle muscle strengthening program is effective for individuals with KOA to reduce pain and improve function.

METHODS

In this randomized controlled trial, individuals diagnosed with clinical and radiographic KOA were randomized into the intervention (supervised foot-ankle strengthening exercise program three times a week for 8 weeks) or control (usual care and recommendations of the healthcare team) group. Effectiveness was assessed by changes in clinical and functional outcomes between baseline and 8 weeks with pain as the primary outcome. ANCOVA tests using the intervention group as a reference and sex, body mass index, and baseline values as covariates assessed between-group differences.

RESULTS

The intervention group showed lower pain scores (-4.4 units; 95%CI = -7.5, -1.1), better function (-7.1 units; 95%CI = -12.7, -1.4), higher total functional score (-11.9 units; 95%CI = -20.7, -3.1), with confidence intervals indicating a potential for the differences to be clinically meaningful, and better scores for the 30-s chair stand test (2.7 repetitions; 95%CI = 1.1, 4.1), with a confidence interval indicating a moderate clinically meaningful difference, compared to the controls.

CONCLUSION

The 8-week foot-ankle exercise program showed positive, and potentially clinically meaningful, effects on knee pain and physical function among individuals with KOA, when compared to usual care.

TRIAL REGISTRATION

NCT04154059. https://clinicaltrials.gov/ct2/show/NCT04154059.

High-Intensity Training for Knee Osteoarthritis: A Narrative Review

Knee osteoarthritis (OA) is the most common joint disease worldwide. Exercise therapy has been identified as a first-line treatment option in patients suffering from knee OA. High-intensity training (HIT) is an innovative exercise modality with potential in improving various disease-related outcomes. The purpose of this review is to explore the impact of HIT on knee OA symptoms and physical functioning. A comprehensive search of scientific electronic databases was conducted to identify articles on the effects of HIT on knee OA. Thirteen studies were included in this review. Ten compared the effects of HIT with those of low-intensity training, moderate-intensity continuous training, or a control group. Three evaluated the effects of HIT alone. Eight reported a decrease in knee OA symptoms (especially pain), and eight reported an increase in physical functioning. HIT was shown to improve knee OA symptoms and physical functioning, but also aerobic capacity, muscle strength, and quality of life with minimal or no adverse events. However, compared with other exercise modalities, no clear superiority of HIT was found. HIT is a promising exercise strategy in patients with knee OA; nonetheless, the actual quality of evidence remains very low, and more high-quality studies are needed to confirm these promising outcomes.

Do Injury-Resistant Runners Have Distinct Differences in Clinical Measures Compared with Recently Injured Runners?

INTRODUCTION

Although lower extremity muscle strength, joint motion, and functional foot alignment are commonly used, time-efficient clinical measures that have been proposed as risk factors for running-related injuries, it is unclear if these factors can distinguish injury resistance in runners.

PURPOSE

This study compares clinical measures, with consideration of sex, between recently injured runners (3 months to 1 yr prior), those with a high level of injury resistance who have been uninjured for at least 2 yr, and never-injured runners.

METHODS

Averaged bilateral values and between-limb symmetry angles of lower limb isometric muscle strength, joint motion, navicular drop, and foot posture index (FPI) were assessed in a cohort of recreational runners, and their injury history was recorded. Differences in clinical measures between injury groupings were examined, with consideration of sex.

RESULTS

Of the 223 runners tested, 116 had been recently injured, 61 had been injured >2 yr ago and were deemed to have acquired reinjury resistance, and 46 were never injured. Plantarflexion was greater in both recently injured (P = 0.001) and acquired reinjury resistance runners (P = 0.001) compared with never-injured runners. Recently injured runners displayed higher hip abduction strength compared with never-injured runners (P = 0.019, η2 = 0.038, small effect size). There were no statistically significant differences in the remaining measures between the injury groupings. With the exception of FPI, there was no interaction between sex and injury grouping for any of the measures.

CONCLUSION

Commonly used clinical measures of strength, joint motion, and functional foot alignment were not superior in injury-resistant runners compared with recently injured runners, questioning their relevance in identifying future injury resistance of runners.

Effect of Active Lengthening and Shortening on Small-Angle X-ray Reflections in Skinned Skeletal Muscle Fibres

Our purpose was to use small-angle X-ray diffraction to investigate the structural changes within sarcomeres at steady-state isometric contraction following active lengthening and shortening, compared to purely isometric contractions performed at the same final lengths. We examined force, stiffness, and the 1,0 and 1,1 equatorial and M3 and M6 meridional reflections in skinned rabbit psoas bundles, at steady-state isometric contraction following active lengthening to a sarcomere length of 3.0 µm (15.4% initial bundle length at 7.7% bundle length/s), and active shortening to a sarcomere length of 2.6 µm (15.4% bundle length at 7.7% bundle length/s), and during purely isometric reference contractions at the corresponding sarcomere lengths. Compared to the reference contraction, the isometric contraction after active lengthening was associated with an increase in force (i.e., residual force enhancement) and M3 spacing, no change in stiffness and the intensity ratio I_1,1/I_1,0, and decreased lattice spacing and M3 intensity. Compared to the reference contraction, the isometric contraction after active shortening resulted in decreased force, stiffness, I_1,1/I_1,0, M3 and M6 spacings, and M3 intensity. This suggests that residual force enhancement is achieved without an increase in the proportion of attached cross-bridges, and that force depression is accompanied by a decrease in the proportion of attached cross-bridges. Furthermore, the steady-state isometric contraction following active lengthening and shortening is accompanied by an increase in cross-bridge dispersion and/or a change in the cross-bridge conformation compared to the reference contractions.

Age-Related Skeletal Muscle Dysfunction Is Aggravated by Obesity: An Investigation of Contractile Function, Implications and Treatment

Obesity is a global epidemic and coupled with the unprecedented growth of the world's older adult population, a growing number of individuals are both old and obese. Whilst both ageing and obesity are associated with an increased prevalence of chronic health conditions and a substantial economic burden, evidence suggests that the coincident effects exacerbate negative health outcomes. A significant contributor to such detrimental effects may be the reduction in the contractile performance of skeletal muscle, given that poor muscle function is related to chronic disease, poor quality of life and all-cause mortality. Whilst the effects of ageing and obesity independently on skeletal muscle function have been investigated, the combined effects are yet to be thoroughly explored. Given the importance of skeletal muscle to whole-body health and physical function, the present study sought to provide a review of the literature to: (1) summarise the effect of obesity on the age-induced reduction in skeletal muscle contractile function; (2) understand whether obesity effects on skeletal muscle are similar in young and old muscle; (3) consider the consequences of these changes to whole-body functional performance; (4) outline important future work along with the potential for targeted intervention strategies to mitigate potential detrimental effects.

Effect of High-Intensity Strength Training on Knee Pain and Knee Joint Compressive Forces Among Adults With Knee Osteoarthritis: The START Randomized Clinical Trial

IMPORTANCE

Thigh muscle weakness is associated with knee discomfort and osteoarthritis disease progression. Little is known about the efficacy of high-intensity strength training in patients with knee osteoarthritis or whether it may worsen knee symptoms.

OBJECTIVE

To determine whether high-intensity strength training reduces knee pain and knee joint compressive forces more than low-intensity strength training and more than attention control in patients with knee osteoarthritis.

DESIGN, SETTING, AND PARTICIPANTS

Assessor-blinded randomized clinical trial conducted at a university research center in North Carolina that included 377 community-dwelling adults (≥50 years) with body mass index (BMI) ranging from 20 to 45 and with knee pain and radiographic knee osteoarthritis. Enrollment occurred between July 2012 and February 2016, and follow-up was completed September 2017.

INTERVENTIONS

Participants were randomized to high-intensity strength training (n = 127), low-intensity strength training (n = 126), or attention control (n = 124).

MAIN OUTCOMES AND MEASURES

Primary outcomes at the 18-month follow-up were Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) knee pain (0 best-20 worst; minimally clinically important difference [MCID, 2]) and knee joint compressive force, defined as the maximal tibiofemoral contact force exerted along the long axis of the tibia during walking (MCID, unknown).

RESULTS

Among 377 randomized participants (mean age, 65 years; 151 women [40%]), 320 (85%) completed the trial. Mean adjusted (sex, baseline BMI, baseline outcome values) WOMAC pain scores at the 18-month follow-up were not statistically significantly different between the high-intensity group and the control group (5.1 vs 4.9; adjusted difference, 0.2; 95% CI, -0.6 to 1.1; P = .61) or between the high-intensity and low-intensity groups (5.1 vs 4.4; adjusted difference, 0.7; 95% CI, -0.1 to 1.6; P = .08). Mean knee joint compressive forces were not statistically significantly different between the high-intensity group and the control group (2453 N vs 2512 N; adjusted difference, -58; 95% CI, -282 to 165 N; P = .61), or between the high-intensity and low-intensity groups (2453 N vs 2475 N; adjusted difference, -21; 95% CI, -235 to 193 N; P = .85). There were 87 nonserious adverse events (high-intensity, 53; low-intensity, 30; control, 4) and 13 serious adverse events unrelated to the study (high-intensity, 5; low-intensity, 3; control, 5).

CONCLUSIONS AND RELEVANCE

Among patients with knee osteoarthritis, high-intensity strength training compared with low-intensity strength training or an attention control did not significantly reduce knee pain or knee joint compressive forces at 18 months. The findings do not support the use of high-intensity strength training over low-intensity strength training or an attention control in adults with knee osteoarthritis.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01489462.

A simple model of cardiac muscle for multiscale simulation: Passive mechanics, crossbridge kinetics and calcium regulation

A simple model of cardiac muscle was designed for multiscale simulation of heart mechanics. Relaxed cardiac muscle was described as a transversally isotropic hyperelastic material. Active tension caused by actin-myosin crossbridges depends on the ensemble averaged strain of myosin heads bound to actin. Calcium activation was modeled by Ca²⁺ binding to troponin-C. To account for the dependence of troponin affinity for Ca²⁺ on myosin heads strongly bound to actin, the kinetics of troponin binding to Ca²⁺ in the overlap zone of the thin and thick filaments and outside it were separated. The changes in the length of these zones during muscle shortening or lengthening were accounted for explicitly. Simplified version of the model contains only 5 ordinary differential equations (ODE). Model parameters were estimated from a limited set of experiments with skeletal and cardiac muscle. Simulations have shown that model reproduces qualitatively a number of experimental observations: steady-state force-velocity and stiffness-velocity relations; mechanical responses to step changes in muscle length or load; steep Ca²⁺-tension relationship and its dependence on sarcomere length tension (the Frank-Starling mechanism); tension, shortening and Ca²⁺-transients in twitch isometric and isotonic contractions, tension development and redevelopment upon fast change in Ca²⁺ concentration or muscle release followed by re-stretch. We believe that the model can be effectively used for modeling contraction and relaxation of the heart.

Possible Cause of Nonlinear Tension Rise in Activated Muscle Fiber during Stretching

Tension in contracting muscle fiber under conditions of ramp stretching rapidly increases, but after reaching a critical stretch P_c sharply decreases. To find out the cause of these changes in muscle fiber tension, we stopped stretching before and after reaching P_c and left the fiber stretched for 50 msec. After rapid tension drop, the transient tension rise not accompanied by fiber stiffness increase was observed only in fibers heated to 25°C and stretched to P_c. Under other experimental conditions, this growth was absent. We suppose that stretch of the fiber to P_c induces transition of stereo-specifically attached myosin heads to pre-power stroke state and when the stretching is stopped, they make their step on actin and generate force. When the tension reaches P_c, all stereospecifically attached myosin heads turn out to be non-stereospecifically, or weakly attached to actin, and are unable to make the force-generating step.

The lifetime of the actomyosin complex in vitro under load corresponding to stretch of contracting muscle

During eccentric contraction, muscle is lengthening so that the actin-myosin cross-bridges bear a load that exceeds the force they generate during isometric contraction. Using the optical trap technique, we simulated eccentric contraction at the single molecule level and investigated the effect of load on the skeletal actomyosin lifetime at different ATP concentrations. The range of the loads was up to 17 pN above the isometric level. We found that the frequency distribution of the lifetime of the actin-bound state of the myosin molecule was biphasic: it quickly rose and then decreased slowly. The rate of the slow phase of this distribution increased with both the load and the ATP concentration. The fast phase accelerated sharply with the load, but it was independent of ATP concentration. The presence of the fast phase demonstrates that some transition(s) in the actomyosin complex occur before the myosin head becomes able to bind ATP and detach from actin. Its high sensitivity to the load indicates that the transition is load-dependent.

Poorly understood aspects of striated muscle contraction

Muscle contraction results from cyclic interactions between the contractile proteins myosin and actin, driven by the turnover of adenosine triphosphate (ATP). Despite intense studies, several molecular events in the contraction process are poorly understood, including the relationship between force-generation and phosphate-release in the ATP-turnover. Different aspects of the force-generating transition are reflected in the changes in tension development by muscle cells, myofibrils and single molecules upon changes in temperature, altered phosphate concentration, or length perturbations. It has been notoriously difficult to explain all these events within a given theoretical framework and to unequivocally correlate observed events with the atomic structures of the myosin motor. Other incompletely understood issues include the role of the two heads of myosin II and structural changes in the actin filaments as well as the importance of the three-dimensional order. We here review these issues in relation to controversies regarding basic physiological properties of striated muscle. We also briefly consider actomyosin mutation effects in cardiac and skeletal muscle function and the possibility to treat these defects by drugs.