Skeletal Muscle Contractile Properties Research Articles

Linking in vivo muscle dynamics to in situ force-length and force-velocity reveals that guinea fowl lateral gastrocnemius operates at shorter than optimal lengths.

The isometric force-length (F-L) and isotonic force-velocity (F-V) relationships characterize the contractile properties of skeletal muscle under controlled conditions, yet it remains unclear how these properties relate to in vivo muscle function. Here, we map the in situ F-L and F-V characteristics of guinea fowl (Numida meleagris) lateral gastrocnemius (LG) to the in vivo operating range during walking and running. We test the hypothesis that muscle fascicles operate on the F-L plateau, near the optimal length for force (L0) and near velocities that maximize power output (Vopt) during walking and running. We found that in vivo LG velocities are consistent with optimizing power during work production, and economy of force at higher loads. However, LG does not operate near L0 at higher loads. LG length was near L0 at the time of EMG onset but shortened rapidly such that force development during stance occurred on the ascending limb of the F-L curve, around 0.8L0. Shortening across L0 in late swing might optimize potential for rapid force development near the swing-stance transition, providing resistance to unexpected perturbations that require rapid force development. We also found evidence of in vivo passive force rise in late swing, without EMG activity, at lengths where in situ passive force is zero, suggesting that dynamic viscoelastic effects contribute to in vivo force development. Comparison of in vivo operating ranges to F-L and F-V properties suggests the need for new approaches to characterize muscle properties in controlled conditions that more closely resemble in vivo dynamics.

Concerted regulation of skeletal muscle metabolism and contractile properties by the orphan nuclear receptor Nr2f6.

The maintenance of skeletal muscle plasticity upon changes in the environment, nutrient supply, and exercise depends on regulatory mechanisms that couple structural and metabolic adaptations. The mechanisms that interconnect both processes at the transcriptional level remain underexplored. Nr2f6, a nuclear receptor, regulates metabolism and cell differentiation in peripheral tissues. However, its role in the skeletal muscle is still elusive. Here, we aimed to investigate the effects of Nr2f6 modulation on muscle biology in vivo and in vitro. Global RNA-seq was performed in Nr2f6 knockdown C2C12 myocytes (N=4-5). Molecular and metabolic assays and proliferation experiments were performed using stable Nr2f6 knockdown and Nr2f6 overexpression C2C12 cell lines (N=3-6). Nr2f6 content was evaluated in lipid overload models in vitro and in vivo (N=3-6). In vivo experiments included Nr2f6 overexpression in mouse tibialis anterior muscle, followed by gene array transcriptomics and molecular assays (N=4), ex vivo contractility experiments (N=5), and histological analysis (N=7). The conservation of Nr2f6 depletion effects was confirmed in primary skeletal muscle cells of humans and mice. Nr2f6 knockdown upregulated genes associated with muscle differentiation, metabolism, and contraction, while cell cycle-related genes were downregulated. In human skeletal muscle cells, Nr2f6 knockdown significantly increased the expression of myosin heavy chain genes (two-fold to three-fold) and siRNA-mediated depletion of Nr2f6 increased maximal C2C12 myocyte's lipid oxidative capacity by 75% and protected against lipid-induced cell death. Nr2f6 content decreased by 40% in lipid-overloaded myotubes and by 50% in the skeletal muscle of mice fed a high-fat diet. Nr2f6 overexpression in mice resulted in an atrophic and hypoplastic state, characterized by a significant reduction in muscle mass (15%) and myofibre content (18%), followed by an impairment (50%) in force production. These functional phenotypes were accompanied by the establishment of an inflammation-like molecular signature and a decrease in the expression of genes involved in muscle contractility and oxidative metabolism, which was associated with the repression of the uncoupling protein 3 (20%) and PGC-1α (30%) promoters activity following Nr2f6 overexpression in vitro. Additionally, Nr2f6 regulated core components of the cell division machinery, effectively decoupling muscle cell proliferation from differentiation. Our findings reveal a novel role for Nr2f6 as a molecular transducer that plays a crucial role in maintaining the balance between skeletal muscle contractile function and oxidative capacity. These results have significant implications for the development of potential therapeutic strategies for metabolic diseases and myopathies.

Sex differences in neuromuscular and biological determinants of isometric maximal force.

Force expression is characterized by an interplay of biological and molecular determinants that are expected to differentiate males and females in terms of maximal performance. These include muscle characteristics (muscle size, fiber type, contractility), neuromuscular regulation (central and peripheral factors of force expression), and individual genetic factors (miRNAs and gene/protein expression). This research aims to comprehensively assess these physiological variables and their role as determinants of maximal force difference between sexes. Experimental evaluations include neuromuscular components of isometric contraction, intrinsic muscle characteristics (proteins and fiber type), and some biomarkers associated with muscle function (circulating miRNAs and gut microbiome) in 12 young and healthy males and 12 females. Male strength superiority appears to stem primarily from muscle size while muscle fiber-type distribution plays a crucial role in contractile properties. Moderate-to-strong pooled correlations between these muscle parameters were established with specific circulating miRNAs, as well as muscle and plasma proteins. Muscle size is crucial in explaining the differences in maximal voluntary isometric force generation between males and females with similar fiber type distribution. Potential physiological mechanisms are seen from associations between maximal force, skeletal muscle contractile properties, and biological markers.

Sensor location affects skeletal muscle contractility parameters measured by tensiomyography.

Tensiomyography (TMG) is a non-invasive method for measuring contractile properties of skeletal muscle that is increasingly being used in research and practice. However, the lack of standardization in measurement protocols mitigates the systematic use in sports medical settings. Therefore, this study aimed to investigate the effects of lower leg fixation and sensor location on TMG-derived parameters. Twenty-two male participants underwent TMG measurements on the m. biceps femoris (BF) in randomized order with and without lower leg fixation (fixed vs. non-fixed). Measurements were conducted at 50% of the muscle's length (BF-mid) and 10 cm distal to this (BF-distal). The sensor location affected the contractile properties significantly, both with and without fixation. Delay time (Td) was greater at BF-mid compared to BF-distal (fixed: 23.2 ± 3.2 ms vs. 21.2 ± 2.7 ms, p = 0.002; non-fixed: 24.03 ± 4.2 ms vs. 21.8 ± 2.7 ms, p = 0.008), as were maximum displacement (Dm) (fixed: 5.3 ± 2.7 mm vs. 3.5 ± 1.7 mm, p = 0.005; non-fixed: 5.4 ± 2.5 mm vs. 4.0 ± 2.0 mm, p = 0.03), and contraction velocity (Vc) (fixed: 76.7 ± 25.1 mm/s vs. 57.2 ± 24.3 mm/s, p = 0.02). No significant differences were revealed for lower leg fixation (all p > 0.05). In summary, sensor location affects the TMG-derived parameters on the BF. Our findings help researchers to create tailored measurement procedures in compliance with the individual goals of the TMG measurements and allow adequate interpretation of TMG parameters.

Iron supplementation improves skeletal muscle contractile properties in mice with chronic kidney disease.

Adult chronic kidney disease (CKD) patients commonly display decreased physical function, leading to increased mortality, which is exacerbated with iron deficiency and anemia. Interventions to mitigate CKD myopathy are scarce, potentially because the underlying contractile deficits have not been fully investigated. We examined single fiber force production, myosin-actin interactions and myofilament properties in soleus and extensor digitorum longus muscles of 16-week-old CKD mice without (CKD, N=12) and with iron supplementation (CKDFE, N=6, weekly injections of 0.2 mg/kg iron dextran) and controls (N=10). Late-stage CKD was induced by 0.2% adenine diet for 8 weeks. CKD with iron supplementation (CKDFE) improved anemia status compared to CKD, but not back to control levels. Maximally activated (pCa 4.5, 25°C) specific tension (maximal isometric force divided by cross-sectional area) was reduced 36-51% with CKD due, in a large part, to a reduction in strongly-bound myosin-actin cross-bridges in all myosin heavy chain (MHC) I, IIA, and IIB fibers. Iron supplementation improved specific tension and number of strongly-bound cross-bridges in MHC IIA and IIB fibers. Myosin-actin cross-bridge kinetics were slower with CKD in MHC I and IIA fibers, with iron supplementation restoring kinetics closer to control values in MHC IIA fibers. Higher hemoglobin levels were correlated to improvements in specific tension and strongly-bound cross-bridges in MHC IIA and IIB fibers, and with faster cross-bridge kinetics in MHC IIA fibers. However, CKD induced decreases in myofilament lattice stiffness for MHC IIA and IIB fibers were not improved with iron supplementation. Our findings show that iron supplementation improved various aspects of the cellular and molecular CKD-induced myopathy in fast-contracting fiber types. Thus, correction of iron imbalance and/or anemia may be an effective countermeasure to reduce contractile deficits and improve quality of life in late-stage CKD patients.

Effects of motor imagery training on skeletal muscle contractile properties in sports science students.

Studies on motor imagery (MI) practice based on different designs and training protocols have reported changes in maximal voluntary contraction (MVC) strength. However, to date, there is a lack of information on the effects of MI training on contractile properties of the trained muscle. Forty-five physically active sport science students (21 female) were investigated who trained three times per week over a 4-week period in one of three groups: An MI group conducted MI practice of maximal isometric contraction of the biceps brachii; a physical exercise (PE) group physically practiced maximal isometric contractions of the biceps brachii in a biceps curling machine; and a visual imagery (VI) group performed VI training of a landscape. A MVC test of the arm flexors was performed in a biceps curling machine before and after 4 weeks of training. The muscular properties of the biceps brachii were also tested with tensiomyography measurements (TMG). Results showed an interaction effect between time and group for MVC (p=0.027, η 2 = 0.17), with a higher MVC value in the PE group (Δ5.9%) compared to the VI group (Δ-1.3%) (p=0.013). MVC did not change significantly in the MI group (Δ2.1%). Analysis of muscle contractility via TMG did not show any interaction effects neither for maximal radial displacement (p=0.394, η 2 = 0.05), delay time (p=0.79, η 2 = 0.01) nor contraction velocity (p=0.71, η 2 = 0.02). In spite of MVC-related changes in the PE group due to the interventions, TMG measurements were not sensitive enough to detect concomitant neuronal changes related to contractile properties.

Effects of Meditation on Cardiovascular and Muscular Responses in Patients during Cardiac Rehabilitation: A Randomized Pilot Study

Background: Cardiovascular diseases are the world’s number one cause of death, with exceeding psychosocial stress load being considered a major risk factor. A stress management technique that has repeatedly shown positive effects on the cardiovascular system is the Transcendental Meditation (TM) technique. The present pilot study aimed to investigate the potential effect of TM on the recovery of cardiac patients. Objectives: We hypothesized that practicing TM in patients undergoing a 4-week cardiac rehabilitation program augments the recovery of cardiovascular parameters and reduces skeletal muscle tone after rehabilitation. Methods: Twenty cardiac patients were recruited and randomly assigned to either the control or the TM group. Cardiovascular parameters were assessed with the Task Force Monitor (TFM) and skeletal muscle contractile properties by Tensiomyography during a sit-stand test, performed at the beginning and end of a 4-week in-patient rehabilitation program. Results: Systolic blood pressure (SBP) was significantly lower after 4 weeks of cardiac rehabilitation, while the RR-interval (RRI) significantly increased. At the skeletal muscle level, the contraction time and maximal displacement increased, though only in the gastrocnemius medialis and biceps femoris muscles and not in vastus lateralis. Group interactions were not observed for hemodynamic parameters nor for muscle contractile properties. Discussion: Although significant improvements in hemodynamic and muscular parameters were observed after 4 weeks of rehabilitation, we could not provide evidence that TM improved rehabilitation after 4 weeks. TM may unfold its effects on the cardiovascular system in the longer term. Hence, future studies should comprise a long-term follow-up.

Isometric skeletal muscle contractile properties in common strains of male laboratory mice.

Assessing contractile function of skeletal muscle in murine models is a commonly employed laboratory technique that investigators utilize to measure the impact of genetic manipulations, drug efficacy, or other therapeutic interventions. Often overlooked is the potential for the strain of the mouse to influence the functional properties of the skeletal muscle. Thus, we sought to characterize commonly assessed isometric force measures in the hindlimb muscles across a variety of mouse strains. Using 6-8-week-old male mice, we measured isometric force, fatigue susceptibility, relaxation kinetics, muscle mass, myofiber cross-sectional area, and fiber type composition of the extensor digitorum longus (EDL) and soleus muscles in C57BL/6NJ, BALB/cJ, FVB/NJ, C57BL/6J, and C57BL/10 mice. The data demonstrate both unique differences and a number of similarities between both muscles in the various genetic backgrounds of mice. Soleus muscle specific force (i.e., force per unit size) exhibited higher variation across strains while specific force of the EDL muscle exhibited minimal variation. In contrast, absolute force differed only in a few mouse strains whereas analysis of muscle morphology revealed many distinctions when compared across all the groups. Collectively, the data suggest that the strain of the mouse can potentially influence the measured biological outcome and may possibly promote a synergistic effect with any genetic manipulation or therapeutic intervention. Thus, it is critical for the investigator to carefully consider the genetic background of the mouse used in the experimental design and precisely document the strain of mouse employed during publication.

Membrane capacitance and characteristic frequency are associated with contractile properties of skeletal muscle.

The cell membrane capacitance (Cm) and characteristic frequencies (fc) of tissues can be obtained using segmental bioelectrical impedance spectroscopy (S-BIS). Higher Cm and lower fc are associated with a larger surface area of skeletal muscle fibers with T-tubules in the tissues. Muscle fiber membrane is one of the major physiological factors that influence surface electromyograms (EMGs) as well as the number of recruited motor units so that the amplitude of surface EMG may be correlated with Cm and fc. The aim of the current study was to examine the association of fc or Cm in the lower leg with contractile and neuromuscular properties in the plantar flexors. We analyzed data from 59 participants (29 women) aged 21-83 years. The Cm, fc, and intracellular water (ICW) in the lower leg were obtained using S-BIS. We measured electrical-evoked torque, maximal voluntary contraction (MVC) torque, and amplitude of EMG normalized by the M wave during MVC contraction. The high Cm group had a significantly lower fc and significantly higher MVC torque, estimated maximum torque, twitch torque, and root mean square (RMS) of EMG normalized by the M wave (EMG:M) in the musculus triceps surae compared to the low Cm group (P<0.05). Cm was positively and fc was negatively correlated with the nRMS of EMG:M in the triceps surae (P<0.05). S-BIS recordings can be used to detect changes in skeletal muscle membrane capacitance, which may provide insights into the number of T-tubules. The muscle capacitance measured with S-BIS can be predictive of muscle force generation.

Iron Supplementation Improves Skeletal Muscle Contractile Properties in Mice with CKD.

Patients with chronic kidney disease (CKD) frequently have compromised physical performance, which increases their mortality; however, their skeletal muscle dysfunction has not been characterized at the single-fiber and molecular levels. Notably, interventions to mitigate CKD myopathy are scarce. The effect of CKD in the absence and presence of iron supplementation on the contractile function of individual skeletal muscle fibers from the soleus and extensor digitorum longus muscles was evaluated in 16-week-old mice. CKD was induced by the adenine diet, and iron supplementation was by weekly iron dextran injections. Maximally activated and fatigued fiber force production was decreased 24%-52% in untreated CKD, independent of size, by reducing strongly bound myosin/actin cross-bridges and/or decreasing myofilament stiffness in myosin heavy chain (MHC) I, IIA, and IIB fibers. Additionally, myosin/actin interactions in untreated CKD were slower for MHC I and IIA fibers and unchanged or faster in MHC IIB fibers. Iron supplementation improved anemia and did not change overall muscle mass in CKD mice. Iron supplementation ameliorated CKD-induced myopathy by increasing strongly bound cross-bridges, leading to improved specific tension, and/or returning the rate of myosin/actin interactions toward or equivalent to control values in MHC IIA and IIB fibers. Skeletal muscle force production was significantly reduced in untreated CKD, independent of fiber size, indicating that compromised physical function in patients is not solely due to muscle mass loss. Iron supplementation improved multiple aspects of CKD-induced myopathy, suggesting that timely correction of iron imbalance may aid in ameliorating contractile deficits in CKD patients.

Skeletal Muscle Dysfunction in Experimental Pulmonary Hypertension Kosmas Kosmas1,2, Zoe Michael2,3, Fotios Spyropoulos1,2, Jeffrey Widrick2,4, Ravi Jasuja2, Aimilia Papathanasiou1,2, Helen Christou 1,21Department of Pediatric Newborn Medicine, Brigham and Women’s Hospital, Boston, MA 02115, USA 2Harvard Medical School, Boston, MA 02215, USA 3Department of Pediatrics, Boston Children’s Hospital, Boston, MA 02215, USA 4Department of Genetics, Boston Children’s Hospital, Boston, MA 02215,

BackgroundPulmonary arterial hypertension (PAH), is a progressive disease that seriously compromises quality of life due to dyspnea and fatigue on exertion that worsens over time such that patients are ultimately immobile. Although hemodynamic compromise is the main contributor to exercise intolerance in PAH, accumulating evidence supports that intrinsic skeletal muscle dysfunction also occurs and may contribute to this symptomatology. We previously showed that treatment with the carbonic anhydrase inhibitor Acetazolamide (ACTZ) ameliorates the hemodynamic components of experimental PAH but its effects on skeletal muscle function and exercise tolerance are unknown. Our objective is to characterize the mechanisms of skeletal muscle dysfunction in a preclinical model of severe PAH and evaluate the effect of ACTZ treatment.HypothesesWe hypothesized that reduced exercise endurance in experimental PAH is associated with increased proportion of fast glycolytic (Type II) fibers to slow oxidative (Type I) fibers, and sarcomeric dysfunction in skeletal muscles and that treatment with ACTZ, alters muscle fiber specificity, improves skeletal muscle contractile properties and exercise tolerance.MethodsWe used the adult rat Sprague Dawley sugen/hypoxia (Su/Hx) model of severe pulmonary hypertension and performed hemodynamic and exercise tolerance studies (treadmill). We evaluated the abundance of Type I and Type II fiber specific markers and sarcomeric organization in muscles from Su/Hx and ACTZ treated rats and measured twitch and tetanic forces, contraction and relaxation times in diaphragm, soleus and extensor digitorum longus (EDL). We used the rat myoblast cell line (L6) to evaluate the molecular mechanisms of muscle fiber switch using immunofluorescence, RNA and protein expression studies.ResultsWe found that diaphragm and soleus muscle from the adult rat sugen/hypoxia (Su/Hx) model of severe PAH have increased abundance of type II fiber markers and thick sarcomeric aggregates and these changes are accompanied by decreased twitch and tetanic forces, contraction and half‐relaxation time and exercise endurance despite absence of muscle atrophy. Acetazolamide (ACTZ), treatment restored the above derangements. In vitro rat myotube differentiation was associated with a predominance of type II fiber markers in conjunction with increased abundance of the transcription factor FoxO1. This pattern of increased abundance of FoxO1 and increased type II markers was also seen in Su/Hx soleus muscles and was reversed in response to ACTZ treatment.ConclusionsWe conclude that a shift in skeletal muscle fiber type specification may underlie skeletal muscle dysfunction in experimental PAH and that treatment with ACTZ may ameliorate skeletal muscle dysfunction through an inhibitory effect on FoxO1‐mediated fiber type specification.

High-throughput, real-time monitoring of engineered skeletal muscle function using magnetic sensing

Engineered muscle tissues represent powerful tools for examining tissue level contractile properties of skeletal muscle. However, limitations in the throughput associated with standard analysis methods limit their utility for longitudinal study, high throughput drug screens, and disease modeling. Here we present a method for integrating 3D engineered skeletal muscles with a magnetic sensing system to facilitate non-invasive, longitudinal analysis of developing contraction kinetics. Using this platform, we show that engineered skeletal muscle tissues derived from both induced pluripotent stem cell and primary sources undergo improvements in contractile output over time in culture. We demonstrate how magnetic sensing of contractility can be employed for simultaneous assessment of multiple tissues subjected to different doses of known skeletal muscle inotropes as well as the stratification of healthy versus diseased functional profiles in normal and dystrophic muscle cells. Based on these data, this combined culture system and magnet-based contractility platform greatly broadens the potential for 3D engineered skeletal muscle tissues to impact the translation of novel therapies from the lab to the clinic.

Lower-Limb Muscle Contractile Properties, Explosive Power and the Subjective Response of Elite Soccer Players to the COVID-19 Lockdown.

The present study examined the effects of the lockdown period on basic anthropometric measures, countermovement jumping performance, skeletal muscle contractile properties derived from tensiomyography (TMG), injury incidence, and self-assessed general well-being in elite soccer players. A total of 266 players were assessed before (PRE) and 32 players were reassessed 11 days after (POST) the COVID-19 period. Significant changes in the TMG parameters were observed POST compared to PRE: contraction time (Tc) increased from 6% to 50% in vastus lateralis [VL] (p = 0.009) and biceps femoris [BF] (p < 0.001), respectively; whereas radial displacement (Dm) increased for 19% in BF (p = 0.036) and 17% in VL (p < 0.001), respectively. Jumping performance remained unchanged from PRE to POST In addition, athletes rated the lockdown period as a positive event and felt psychologically better during the lockdown, primarily because they spent more time with family members and friends. Although there were no differences in any of the variables describing lower limb muscle power following the two-month lockdown, the altered contractile properties of the assessed muscles suggest suboptimal conditioning of the football players.

Krüppel-like factor 10 regulates the contractile properties of skeletal muscle fibers in mice.

Klf10 is a member of the Krüppel-like family of transcription factors, which is implicated in mediating muscle structure (fiber size, organization of the sarcomere), muscle metabolic activity (respiratory chain), and passive force. The aim of this study was to further characterize the roles of Klf10 in the contractile properties of skeletal muscle fibers. Fifty-two single fibers were extracted from female wild-type (WT) and Klf10 knockout (KO) oxidative (soleus) and glycolytic (extensor digitorum longus [EDL]) skinned muscles. Each fiber was immersed successively in relaxing (R), washing (W), and activating (A) solutions. Calcium was included in the activating solution to induce a maximum contraction of the fiber. The maximum force (Fmax ) was measured and normalized to the cross-sectional area to obtain the maximum stress (Stressmax ). After a steady state in contraction was reached, a quick stretch-release was performed; the force at the maximum stretch (Fstretch ) was measured and the stiffness was assessed. Deletion of the Klf10 gene induced changes in the contractile parameters (Fmax , Stressmax , Stiffness), which were lower and higher for soleus and EDL fibers compared with littermates, respectively. These measurements also revealed changes in the proportion and resistance of attached cross-bridges. Klf10 plays a major role in the homeostasis of the contractile behavior of skeletal muscle fibers in a muscle fiber type-specific manner. These findings further implicate important roles for Klf10 in skeletal muscle function and shed new light on understanding the molecular processes regulating the contractility of skeletal muscle fibers.

Effects of temperature on the locomotor performance and contraction properties of skeletal muscle from two Phrynocephalus lizards at high and low altitude.

Locomotor performance and skeletal muscle contraction are critical for animals andare susceptible tochanges in the externalthermal environment, especially for ectotherms. Phrynocephalus erythrurus,which isendemic tothe Qinghai-Tibetan plateau, is known for living at the highest elevation among all reptiles in the world (4500-5300m). In this study, which comparesP. erythrurus withthe lowland Phrynocephalus przewalskii, we evaluated the locomotor performance at different body temperatures, the effects of temperature and oxygen partial pressure (PO2) on the contractile properties of iliofibularis (IF) muscle in vitro, ATPase activity of IF muscle at different temperatures, and the fiber types of IF muscle. Lowland P. przewalskii runs significantly faster than highland P. erythrurus at all test body temperatures. Almost all contractile properties of the IF muscle of P. przewalskii were better than that of P. erythrurus under all test temperatures and PO2. However, P. erythrurus could achieve both optimal isometric (e.g., dPo/dt) and optimal isotonic (e.g., Vmax) contraction at a lower temperature compared with P. przewalskii. Multi-factor analysis further revealed that temperature has a significant effect on the contractile properties of IF muscle for both species. Although the proportion of fibers types and ATPase activities of IF muscle have no significant interspecies difference, the changing pattern of ATPase activities with temperature is consistent with certain contractile properties and locomotor performance. The interspecies differences in locomotor ability and contractile properties of skeletal muscle in high- and low-altitude lizards may be the results of long-term adaptation tothe local environment.

Membrane Capacitance and Characteristic Frequency are Associated with Contractile Properties of Skeletal Muscle

Membrane Capacitance and Characteristic Frequency are Associated with Contractile Properties of Skeletal Muscle

Six weeks of localized heat therapy does not affect muscle mass, strength and contractile properties in healthy active humans.

Animal and human studies have shown that repeated heating may induce skeletal muscle adaptations, increasing muscle strength. The aim of this study is to investigate the effect of 6weeks of localized heating on skeletal muscle strength, volume and contractile properties in healthy humans. Fifteen active participants (8 males/7 females, 35 ± 6 years, 70 ± 14kg, 173 ± 7cm, average training of 87min per week) were subjected to 6weeks of single-leg heat therapy. Heat pads were applied for 8h/day, 5days/week, on one randomly selected calf of each participant, while the contralateral leg acted as control. The heat pads increased muscle temperature by 4.6 ± 1.2°C (p < 0.001). Every 2weeks, participants were tested for morphological (MRI), architectural (ultrasound), contractile (electrically evoked twitch), and force (isometric and isokinetic) adaptations. Repeated localized heating did not affect the cross-sectional area (p = 0.873) or pennation angle (p = 0.345) of the gastrocnemius muscles; did not change the evoked peak twitch amplitude (p = 0.574) or rate of torque development (p = 0.770) of the plantar flexors; and did not change maximal voluntary isometric (p = 0.214) or isokinetic (p = 0.973) plantar flexor torque. Whereas previous studies have observed improved skeletal muscle function following whole-body and localized heating in active and immobilized humans, respectively, the current data suggested that localized heating may not be a potent stimulus for muscle adaptations in active humans.

Effect of exercise and vitamin D on insulin like growth factor-1 level and skeletal muscle autophagy in diabetic rats

Background: diabetic myopathy is one of chronic complications of diabetes mellitus, which is evidenced by muscle weakness and atrophy. In our research we aimed to evaluate the protective role of exercise and vitamin D on diabetic induced changes in the skeletal muscles. Methods: Fourty male Sprague Dawely rats were divided into control, diabetic, exercised diabetic, vitamin D treated diabetic and combined exercise and vitamin D diabetic rats. Fasting blood glucose, fasting insulin, HOMA-IR, serum IGF-1 level as well as the contractile properties of soleus and tibialis anterior muscles were measured. Also western blot analysis for measuring (LC3) and histopathological examination of both muscles were done. Results: in diabetic rats, fasting blood glucose, fasting insulin, HOMA-IR and LC3 (microtubule associated protein-1 light chain-3) expression in muscles were increased whereas serum IGF-1 level was decreased and the contractile properties of skeletal muscles were deteriorated. Vitamin D treatment decreased fasting blood glucose, fasting insulin, HOMA-IR and expression of LC3 but it increased serum IGF-1 with improvement in the skeletal muscles contractility. Also exercised diabetic rats revealed improvement in all biochemical parameters, autophagy marker expression with further improvement in the skeletal muscles contractility. Combining exercise and vitamin D treatment showed a more improvement in all studied parameters and the histopathological examination confirmed our results. Conclusion: regular exercise and vitamin D protect the muscles from diabetic induced lesions by improving glycemic state, serum level of IGF-1and suppressing autophagy which finally reflected on the contractile parameters of the muscles.

Sports Injury Model For Effective Prevention, Diagnostic And Rehabilitation

In order to develop a model for a safe and effective return to sport after injuries, it is important to identify the risk factors associated with the occurrence of an injury. For the first time, we introduce the Tensiomyography (TMG) in the field of sport injuries (SI), a non-invasive and selective tool for the assessment of skeletal muscle contractile properties. As a recommendation from former experiences, a FC Barcelona documented a Muscle Injuries Clinical Guide 3.0 that explicitly emphasizes the use of TMG for the follow-up of muscle functional recovery and to help decide when the athlete can return to play. PURPOSE: To develop a thigh SI prediction model and explore factors of safe return to play. METHODS: The ongoing research project aims to monitor SI epidemiology in Slovenian premium soccer clubs. We monitored TMG of vastus lateralis and medialis, rectus femoris, biceps femoris and semitendinosus of both legs; body characteristics (body height, mass and fat), motor tasks (strength endurance in hamstrings; explosive lower-body strength, flexibility of lower body). RESULTS: Based on 11 thigh SI we were able to predict four (sensitivity 27%, specificity 99%). When predicting only 6 biceps femoris hamstring SI we could predict 4 (sensitivity 80%, specificity 100%). The predictive factors were derived only from TMG parameters. It appears that the worst-case scenario for the SI occurrence of biceps femoris is it short TMG-derived contraction time, high biceps femoris tone and low lateral symmetry. Interestingly, there were no significant predictors from body characteristics and motor tasks. CONCLUSION: Twenty-seven percent of all thigh SI and 80% of hamstring SI could be predicted solely from simple-to-use and non-invasive TMG screening. It seems that short contraction time (previously linked to high proportion of type II muscle fibers) and high muscle tone are risk factor for hamstring injuries, especially where imbalances between both lateral sides were present. Supported by Slovenian Research Agency (research core funding no. L5-8245).

Ultrasound Measurement of Skeletal Muscle Contractile Parameters Using Flexible and Wearable Single-Element Ultrasonic Sensor.

Skeletal muscle is considered as a near-constant volume system, and the contractions of the muscle are related to the changes in tissue thickness. Assessment of the skeletal muscle contractile parameters such as maximum contraction thickness (), contraction time (), contraction velocity (), sustain time (), and half-relaxation () provides valuable information for various medical applications. This paper presents a single-element wearable ultrasonic sensor (WUS) and a method to measure the skeletal muscle contractile parameters in A-mode ultrasonic data acquisition. The developed WUS was made of double-layer polyvinylidene fluoride (PVDF) piezoelectric polymer films with a simple and low-cost fabrication process. A flexible, lightweight, thin, and small size WUS would provide a secure attachment to the skin surface without affecting the muscle contraction dynamics of interest. The developed WUS was employed to monitor the contractions of gastrocnemius (GC) muscle of a human subject. The GC muscle contractions were evoked by the electrical muscle stimulation (EMS) at varying EMS frequencies from 2 Hz up to 30 Hz. The tissue thickness changes due to the muscle contractions were measured by utilizing a time-of-flight method in the ultrasonic through-transmission mode. The developed WUS demonstrated the capability to monitor the tissue thickness changes during the unfused and fused tetanic contractions. The tetanic progression level was quantitatively assessed using the parameter of the fusion index (FI) obtained. In addition, the contractile parameters (, , , , and ) were successfully extracted from the measured tissue thickness changes. In addition, the unfused and fused tetanus frequencies were estimated from the obtained FI-EMS frequency curve. The WUS and ultrasonic method proposed in this study could be a valuable tool for inexpensive, non-invasive, and continuous monitoring of the skeletal muscle contractile properties.