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Given their importance in predicting clinical outcomes, cardiorespiratory fitness (CRF) and muscle status can be considered new vital signs. However, they are not routinely evaluated in healthcare settings. Here, we present a comprehensive review of the epidemiological, mechanistic, and practical bases of the evaluation of CRF and muscle status in adults in primary healthcare settings. We highlight the importance of CRF and muscle status as predictors of morbidity and mortality, focusing on their association with cardiovascular and metabolic outcomes. Notably, adults in the best quartile of CRF and muscle status have as low as one-fourth the risk of developing some of the most common chronic metabolic and cardiovascular diseases than those in the poorest quartile. The physiological mechanisms that underlie these epidemiological associations are addressed. These mechanisms include the fact that both CRF and muscle status reflect an integrative response to the body function. Indeed, muscle plays an active role in the development of many diseases by regulating the body’s metabolic rate and releasing myokines, which modulate metabolic and cardiovascular functions. We also go over the most relevant techniques for assessing peak oxygen uptake as a surrogate of CRF and muscle strength, mass, and quality as surrogates of muscle status in adults. Finally, a clinical case of a middle-aged adult is discussed to integrate and summarize the practical aspects of the information presented throughout. Their clinical importance, the ease with which we can assess CRF and muscle status using affordable techniques, and the availability of reference values, justify their routine evaluation in adults across primary healthcare settings.

We carried out a randomized, clinical trial in adults of both sexes with metabolic syndrome (MS) to assess the efficacy of high-intensity, low-volume interval training (HIIT) compared to moderate-intensity continuous training (MICT) on insulin resistance (IR), muscle mass, muscle activation, and serum musclin. Fasting glycemia, insulinemia, and glycated haemoglobin were determined by conventional methods, IR by Homeostatic model assessment (HOMA), lean mass by Dual-Energy X-ray Absorptiometry, muscle activation through carnosine by Proton Magnetic Resonance Spectroscopy, and musclin by Enzyme-Linked ImmunoSorbent Assay before and after a supervised, three-times/week, 12-week treadmill programme. HIIT (n = 29) consisted of six intervals with one-minute, high-intensity phases at 90% of peak oxygen consumption (VO2peak). MICT (n = 31) trained at 60% of VO2peak for 30 min. Patients had a mean age of 50.8 ± 6.0 years, body mass index of 30.6 ± 4.0 kg/m2, and VO2peak of 29.0 ± 6.3 mL.kg−1.min−1. Compared to MICT, HIIT was not superior at reducing Ln HOMA-IR (adjusted mean difference: 0.083 [95%CI − 0.092 to 0.257]), carnosine or musclin or at increasing thigh lean mass. HIIT increased carnosine by 0.66 mmol/kg.ww (95% CI 0.08–1.24) after intervention. Both interventions reduced IR, body fat percentage and increased total lean mass/height2 and VO2peak. Musclin showed a non-significant reduction with a small effect size after both interventions. Compared to MICT, HIIT is not superior at reducing IR, carnosine or musclin or at increasing skeletal muscle mass in adults with MS. Both training types improved IR, muscle mass and body composition. NCT03087721, March 22nd, 2017. NCT03087721. Registered March 22nd, 2017.

Background: We studied whether musclin function in humans is related to glycemic control, body composition, and cardiorespiratory capacity.Methods: A cross-sectional study was performed in sedentary adults with or without metabolic syndrome (MS). Serum musclin was measured by enzyme-linked immunosorbent assay. Insulin resistance (IR) was evaluated by the homeostatic model assessment (HOMA-IR). Body composition was determined by dual-energy X-ray absorptiometry and muscle composition by measuring carnosine in the thigh, a surrogate of fiber types, through proton magnetic resonance spectroscopy. Cardiorespiratory capacity was assessed through direct ergospirometry.Results: The control (n=29) and MS (n=61) groups were comparable in age (51.5±6.5 years old vs. 50.7±6.1 years old), sex (72.4% vs. 70.5% women), total lean mass (58.5%±7.4% vs. 57.3%±6.8%), and peak oxygen consumption (VOpeak) (31.0±5.8 mL O2./kg.min vs. 29.2±6.3 mL O2/kg.min). Individuals with MS had higher body mass index (BMI) (30.6±4.0 kg/m2 vs. 27.4± 3.6 kg/m2), HOMA-IR (3.5 [95% confidence interval, CI, 2.9 to 4.6] vs. 1.7 [95% CI, 1.1 to 2.0]), and musclin (206.7 pg/mL [95% CI, 122.7 to 387.8] vs. 111.1 pg/mL [95% CI, 63.2 to 218.5]) values than controls (P˂0.05). Musclin showed a significant relationship with HOMA-IR (β=0.23; 95% CI, 0.12 to 0.33; P˂0.01), but not with VOpeak, in multiple linear regression models adjusted for age, sex, fat mass, lean mass, and physical activity. Musclin was significantly associated with insulin, glycemia, visceral fat, and regional muscle mass, but not with BMI, VCO2peak, maximum heart rate, maximum time of work, or carnosine.Conclusion: In humans, musclin positively correlates with insulinemia, IR, and a body composition profile with high visceral adiposity and lean mass, but low body fat percentage. Musclin is not related to BMI or cardiorespiratory capacity.

The aim of the study was to evaluate the safety of high-intensity, low-volume interval training (HIIT-low volume) compared with moderate-intensity continuous aerobic training (MICT) in adults with metabolic syndrome.This is a controlled, randomized, clinical trial in patients without history of ischemic heart disease or diabetes, who underwent a supervised, 3 sessions/week, 12-week treadmill exercise program. The HIIT-low volume (n = 29) sessions consisted of 6 intervals with 1-minute, high-intensity phases at 90% of peak oxygen consumption (VO2peak). The MICT (n = 31) trained at 60% of VO2peak for 30 minutes. A new approach to record and classify all clinical events according to possible causality based on Naranjo's algorithm was developed.Patients were 50.8 ± 6.0 years old, 70% women, with body mass index of 30.6 ± 4.0 kg/m2 and VO2peak of 29.0 ± 6.3 mL·kg-1·min-1. In total, 60 clinical events were recorded in the HIIT-low volume group and 48 in the MICT group, with 59.3% classified as general disease. Only 21 events were classified as adverse reactions possibly related to exercise, without any serious adverse reactions. Both interventions had a similar incidence of musculoskeletal events (incidence rate ratio, 1.1; 95% confidence interval, 0.6-1.8), but HIIT-low volume had a higher incidence of cardiovascular events (incidence rate ratio, 2.9; 95% CI, 0.4-22.8) after adjusting for age, sex, and body mass index (HIIT-low volume: chest pain [n = 1] and symptoms of venous insufficiency of lower limbs [n = 2]; MICT: chest pain [n = 1]).The HIIT-low volume and MICT are safe in patients with metabolic syndrome. We recommend a muscle-conditioning program prior to both and to avoid HIIT-low volume in treadmill in patients with venous insufficiency of the lower limbs.Trial registration number NCT03087721.

The classical approach for calibrating non-ratiometric fluorescent Ca2+ dyes entails the measurement of the fluorescence maximum (Fmax) and minimum (Fmin), as well as the dissociation constant (Kd) of the Ca2+—Dye reaction (model 1). An alternative equation does not need the Fmin but requires the rate constants kon and koff (model 2). However, both approaches are experimentally time consuming and the rate constants for several dyes are unknown. Here, we propose a set of equations (model 3) that simplify the calibration of fluorescent Ca2+ transients obtained with non-ratiometric dyes. This equation allows the calibration of signals without using the Fmin: [Ca2+] = Kd(F − Frest/Fmax − F) + [Ca2+]IR(Fmax − Frest/Fmax − F), where [Ca2+]IR is the resting [Ca2+]. If the classical calibration approach is followed, the Fmin can be estimated from: Fmin = Frest − ([Ca2+]IR(Fmax − Frest)/Kd). We tested the models’ performance using signals obtained from enzymatically dissociated flexor digitorum brevis fibers of C57BL/6 mice loaded with Fluo-4, AM. Model 3 performed the same as model 2, and both gave peak [Ca2+] values 15 ± 0.3% (n = 3) lower than model 1, when we used our experimental Fmin (1.24 ± 0.11 A.U., n = 4). However, when we used the mathematically estimated Fmin (6.78 ± 0.2 A.U) for model 1, the peak [Ca2+] were similar for all three models. This suggests that the dye leakage makes a correct determination of the Fmin unlikely and induces errors in the estimation of [Ca2+]. In conclusion, we propose simpler and time-saving equations that help to reliably calibrate cytosolic Ca2+ transients obtained with non-ratiometric fluorescent dyes. The use of the estimated Fmin avoids the uncertainties associated with its experimental measurement.

Nelson Ivan Cupitra, Juan C Calderón, Raul Narvaez-Sanchez Physiology and Biochemistry Research Group-PHYSIS, Faculty of Medicine, University of Antioquia, Medellin, ColombiaCorrespondence: Raul Narvaez-Sanchez Carrera 51 D #62-29, Office 203, Medellin, ColombiaTel +57 42196030Email raul.narvaez@udea.edu.coAim: To contribute to the knowledge about the mechanisms involved in aortic stiffness due to ageing.Materials and Methods: Aortic rings from young (1.5± 0.5 months, 0.8± 0.2 kg), adult (6± 0.5 months, 2.7± 0.5 kg) and old (28± 8 months, 3.2± 0.8 kg) male New Zealandrabbits were used to evaluate: 1) intima-media thickness by optical microscopy; 2) vascular reactivity (VR) in terms of sensitivity (pD2) and efficacy (Emax) to KCl; phenylephrine (PE); U-46619, a thromboxane A2 receptor agonist, TXA2; carbachol (CCh), isoproterenol and sodium nitroprusside (SNP), using organ bath experiments; and 3) the expression of receptors α 1, β 2 and thromboxane-prostanoids (TP), by immunofluorescence.Results: Ageing 1) did not change the thickness of tunica; 2) significantly reduced the pD2 to KCl, increased the pD2 to PE and reduced both the pD2 and Emax to TXA2, CCh and isoproterenol, and reduced the pD2 to SNP; and 3) significantly increased the expression of α 1 and β 2 receptors in the intima and adventitia, and the expression of TP only in the adventitia.Conclusion: Our results suggest that ageing makes the aorta more reactive to α 1 adrenergic contraction, and it could be a compensation for lower responsiveness to prostanoids. The aged aorta is less reactive to endothelium-dependent and non-dependent relaxation, and the vessel seems to try to compensate for that stiffness increasing β 2 receptors, although probably less functional. These results complement the proposed mechanisms of elastocalcinosis and smooth muscle rigidity, expanding the vision that should guide the treatment of aortic stiffness due to aging.Keywords: ageing, aortic rings, vascular reactivity, vascular smooth muscle, vascular stiffness

Despite the growing concerns related to the potential of long-term pulmonary sequelae due to COVID-19, data about intermediate and long-term changes in the respiratory function of patients who recover is relatively sparse, particularly in developing countries.To assess the characteristics and pulmonary function at follow-up in a sample of Ecuadorian patients that recovered from the virus.We conducted a cross-sectional study that included 43 patients after symptomatic COVID infection, who were evaluated by spirometry, single breath DLCO, and 6MWT. For statistical analysis we performed point biserial correlations, and chi squared tests.Overall, 30.3% of patients (n = 13) reported persistent symptoms, with fatigue being the most common (23.3%, n = 10). Around 34.9% (n = 15) of the sample had a restrictive spirometry pattern, 18.6% (n = 8) had an abnormally decreased adjusted DLCO. A restrictive spirometry pattern was associated with an abnormally low adjusted DLCO (χWe found that a considerable proportion of patients presented with persistent symptoms and alterations in pulmonary function following COVID-19, mainly a restrictive respiratory pattern and abnormally low DLCO. Further studies are needed to determine which patients may benefit from the follow-up with specific pulmonary function tests.

We carried out a randomized, clinical trial in adults of both sexes with metabolic syndrome (MS) to assess the efficacy of high-intensity, low-volume interval training (HIIT) compared to moderate-intensity continuous training (MICT) on insulin resistance (IR), muscle mass, muscle activation, and serum musclin.Fasting glycemia, insulinemia, and glycated haemoglobin were determined by conventional methods, IR by Homeostatic model assessment (HOMA), lean mass by Dual-Energy X-ray Absorptiometry, muscle activation through carnosine by Proton Magnetic Resonance Spectroscopy, and musclin by Enzyme-Linked ImmunoSorbent Assay before and after a supervised, three-times/week, 12-week treadmill programme. HIIT (n = 29) consisted of six intervals with one-minute, high-intensity phases at 90% of peak oxygen consumption (VOPatients had a mean age of 50.8 ± 6.0 years, body mass index of 30.6 ± 4.0 kg/mCompared to MICT, HIIT is not superior at reducing IR, carnosine or musclin or at increasing skeletal muscle mass in adults with MS. Both training types improved IR, muscle mass and body composition. NCT03087721, March 22nd, 2017.NCT03087721. Registered March 22nd, 2017.

Objective: The aim of this study was to compare the effects of low-volume, high-intensity interval training (HIIT) or moderate-intensity continuous training (MICT) on body composition in adults with metabolic syndrome (MS). Methods: This is a post hoc analysis of the randomized clinical trial Intraining-MET. Sixty adults (40–60 years old) were randomized to an MICT (n = 31) or HIIT (n = 29) supervised programme 3 days/week for 12 weeks. MICT sessions were conducted for 36 min at 60% of peak oxygen consumption (VO2peak). HIIT sessions included 6 intervals at 90% VO2peak for 1 min, followed by 2 min at 50% VO2peak. Body composition was assessed with dual energy X-ray absorptiometry. Results: Body weight did not change from pre- to post-training in either MICT (78.9 ± 15.6 kg; 77.7 ± 16.5 kg, p = 0.280) or HIIT groups (76.3 ± 13.4 kg; 76.3 ± 13.7 kg, p = 0.964). Body fat percentage and fat mass (FM) decreased post-training in the MICT (−0.9%; 95% confidence interval [CI]: −0.27 to −1.47 and −0.7 kg; 95% CI: −0.12 to −1.30) and HIIT groups (−1.0%; 95% CI: −0.32 to −1.68 and −0.8 kg; 95% CI: −0.17 to −1.47). Compared to the HIIT programme, MICT significantly reduced android FM (−0.14 kg; 95% CI: −0.02 to −0.26). Lean mass (LM) increased post-training in MICT (+0.7 kg; 95% CI: 0.01–1.41) and HIIT groups (+0.9 kg; 95% CI: 0.12–1.64), but only HIIT increased the trunk LM (+0.6 kg; 95% CI: 0.06–1.20). Conclusions: Both MICT and HIIT reduced FM without changing body weight in adults with MS. MICT had additional benefits by reducing the android FM, whereas HIIT seemed to increase LM. Given the characteristics of the post hoc analysis, further research is required to confirm these results.

Background: Spiders are among the most venomous animals in nature. Their venom constitutes a source of novel and innovative peptides and proteins with medicinal and biotechnological interest. However, their potential as antimicrobial, anti-cancerous, anti-hypertensive and even in the modulation of nociception is under-studied, mainly because handling the venom is technically challenging and there is paucity of next-generation-sequencing (NGS) data. Due to the increasing evidence of underestimation of the number of genes by the use of a single transcriptome assembler, we re-assembled and optimized the de novo transcriptome of the venom gland of the recently described Colombian spider P. verdolaga, by using three free access algorithms: Trinity, Soapdenovo and SPAdes. All the assemblies were evaluated by statistical parameters (e.g. contigs, GC%, max and min length and N50), by applying BUSCO´s terms retrieval against the arthropod data set to determine the best assembly for each software.Results: Our analyses show that while approximately 54% of all the assembled and structurally annotated sequences could be found in all three algorithms, around 23% of these were unique for Trinity and 21% were unique for SPAdes. The non-redundant merge of all three assemblies’ output permitted the annotation of 8640 sequences; at least 15% more when compared to each software separately, and an increase of 20% when compared to a previous P. verdolaga assembly. Analysis of the annotated genes allowed the identification of unreported lectins, kinins and over 200 peptides and proteins with potential antimicrobial and protease inhibition activities. Furthermore, homology search against the Arachnoserver database and the EROP knowledgebase allowed the identification of 135 novel theraphotoxins of biotechnological interest.Conclusion: Transcriptomic data is of utmost importance for spiders, as it is one of the more feasible and scalable ways to characterize these organisms. However, the use of a single de novo assembler implies an under representation of the expressed sequences, as it has been shown here. In the generation of data for non-model organisms as well as in the search for novel peptides and proteins with biotechnological interest, it is highly recommended that at least two different assemblers are employed.

OBJECTIVES The mechanistic understanding of vascular functional impairment during preservation time helps determine the optimal time frame in which explanted arteries can be used. The method of choice is to measure vascular reactivity and receptor expression. Our goal was to study the influence of preservation for 24 and 48 h on vascular reactivity and receptor expression in rabbit aorta. METHODS Aortic rings preserved in Krebs–Henseleit solution were evaluated fresh (t0), 24 h (t24) and 48 h (t48) after harvest for (i) vascular reactivity as sensitivity (pD2) and maximum effect in response to potassium chloride, U46619 (thromboxane-A2 agonist), phenylephrine, carbachol and isoproterenol, in an organ bath; and for (ii) expression of α1, β2 and thromboxane-prostanoid receptors, by immunofluorescence. RESULTS Compared to the control, after 24 h of preservation, potassium chloride-induced pD2 increased a significant 3.6%, whereas U46619-induced vasoconstriction decreased 9%. None of the agonists affected vasodilation. Intimal and medial α1 receptor expression increased 2.5-fold. After 48 h of preservation, α1 expression and vasoconstrictor responses remained similar to those after 24 h of preservation, but in vasodilation the carbachol-induced maximum effect decreased 30% whereas isoproterenol-induced pD2 increased 4% and the maximum effect increased 10%. TP and β2 expression in the intima and media increased 1.8- and 2.5-fold, respectively. CONCLUSIONS Up to 48 h of preservation, the adrenergic pathway and its receptors support vasoconstriction and vasodilation, despite a significant deterioration in the prostanoid pathway.

Background Mag-Fluo-4 is increasingly employed for studying Ca2+ signaling in skeletal muscle; however, the lack of information on the Ca2+-Mag-Fluo-4 reaction limits its wider usage. Methods Fluorescence and isothermal titration calorimetry (ITC) experiments were performed to determine the binding stoichiometry (n) and thermodynamics (enthalpy (ΔH) and entropy (ΔS) changes), as well as the in vitro and in situ Kd of the Ca2+-Mag-Fluo-4 reaction. Rate constants (kon, koff), fluorescence maximum (Fmax), minimum (Fmin), and the dye compartmentalization were also estimated. Experiments in cells used enzymatically dissociated flexor digitorum brevis fibres of C57BL6, adult mice, loaded at room temperature for 8 min, with 6 μM Mag-Fluo-4, AM, and permeabilized with saponin or ionomycin. All measurements were done at 20 °C. Results The in vitro fluorescence assays showed a binding stoichiometry of 0.5 for the Ca2+/Mag-Fluo-4 (n = 5) reaction. ITC results (n = 3) provided ΔH and ΔS values of 2.3 (0.7) kJ/mol and 97.8 (5.9) J/mol.K, respectively. The in situ Kd was 1.652 × 105μM2(n = 58 fibres, R2 = 0.99). With an Fmax of 150.9 (8.8) A.U. (n = 8), Fmin of 0.14 (0.1) A.U. (n = 10), and ΔF of Ca2+ transients of 8.4 (2.5) A.U. (n = 10), the sarcoplasmic [Ca2+]peak reached 22.5 (7.8) μM. Compartmentalized dye amounted to only 1.1 (0.7)% (n = 10). CONCLUSIONS: Two Mag-Fluo-4 molecules coalesce around one Ca2+ ion, in an entropy-driven, very low in situ affinity reaction, making it suitable to reliably track the kinetics of rapid muscle Ca2+ transients. General significance Our results may be relevant to the quantitative study of Ca2+ kinetics in many other cell types.

Common chronic conditions such as metabolic syndrome and diabetes are increasingly associated to metabolic and cardiovascular complications. Although Phyllanthus tenellus leaves have been used in decoctions as a popular remedy to control blood glucose levels and hypertension, its use needs a scientific basis. This study was therefore undertaken to report a phytochemical analysis of P. tenellus leaves and to test if the main active compound has potential to simultaneously tackle several pathophysiological features of metabolic syndrome and diabetes-related metabolic and vascular disorders such as hyperglycaemia, increased platelet activation, and endothelial dysfunction. We performed a partition of the methanolic extract of P. tenellus leaves among different organic solvents followed by chromatographic separation guided by the rat liver microsomal glucose-6-phosphatase assay. Two known tannins were identified by spectroscopic methods as pinocembrin-7-O-[3″-O-galloyl-4″,6″-(S)-hexahydroxydiphenoyl]-α-D-glucose, named P7OG by us, and gemin D. The structural determination of the isolated compounds was based on spectral data. The ability of the main active component, P7OG, to inhibit human platelet aggregation and to modify vascular reactivity of rat aortic rings incubated with high glucose (D-glucose 55 mM) was then evaluated. P7OG was further able to inhibit platelet aggregation induced by adenosine 5′-diphosphate and collagen, showed vasorelaxant effects in arteries precontracted with phenylephrine, and reverted the endothelium-dependent impairment effect of high glucose in rat aortic rings. In conclusion, one tannin isolated from P. tenellus showed promising metabolic, antiaggregant, and vascular effects, which suggests the potential beneficial use of P. tenellus to tackle complex cardiometabolic diseases.

Centruroides margaritatus scorpion stings are common in Colombia. However, the cardiovascular toxicity of the venom has not been clarified. Aim: To study the effect and mechanisms of action of the complete venom of C. margaritatus (CmV) on the murine cardiovascular system. Methods: We evaluated the in vivo effect of CmV LD50 on the mean arterial pressure (MABP), heart rate, and surface electrocardiogram in male adult normotensive Wistar rats. Ex vivo, we evaluated the vascular reactivity of rat aortic rings to increasing concentrations (1 to 60 μg/mL) of CmV using the blockers L-NAME, indomethacin, seratrodast, and prazosin. Results: In the first hour of poisoning, CmV increased the MABP. In the second hour after poisoning, the heart rate decreased as the normalized PR interval and QT corrected increased. After that, cardiovascular shock was demonstrated by a drastic fall in the MABP and signs of cardiac conduction system block. In aortic rings, CmV caused a direct vasoconstrictor effect mediated by alpha-1 adrenergic receptors and counteracted by nitric oxide. Conclusion: The direct vascular and probably the cardiac alpha-1 effects likely explain the transient hypertension and the maintenance of cardiac function, while interval lengthening may be due to K+ channel blockage. Afterwards, the effects of both the alpha-1 pathway and the K+ channel pathway converged, resulting in fatal cardiovascular shock. This knowledge could aid in understanding the dynamics of the effects of the venom and in designing treatments to address its cardiovascular effects.

Metabolic dysfunction in skeletal muscle contributes to the aetiology and development of muscle diseases and metabolic diseases. As such, assessment of skeletal muscle cellular bioenergetics provides a powerful means to understand the role of skeletal muscle metabolism in disease and to identify possible therapeutic targets. Here, we developed a method that allows for the real-time assessment of cellular respiration in intact skeletal muscle fibre bundles obtained from the extensor digitorum longus (EDL) muscle of adult mice. Using this method, we assessed the contribution of ATP turnover and proton leak to basal mitochondrial oxygen consumption rate (OCR). Our data demonstrate that the mitochondria in EDL fibres are loosely coupled. Moreover, in the presence of carbonyl cyanide-p-trifluoromethoxyphenylhydrazone (FCCP), we show that palmitate exposure induced comparable peak OCR and higher total OCR in EDL fibre bundles when compared to pyruvate exposure, suggesting that fatty acids might be a more sustainable fuel source for skeletal muscle when mitochondria are driven to maximal respiration. Application of this method to EDL fibre bundles obtained from chronic high-fat diet fed mice revealed lower basal OCR and enhanced mitochondrial oxidation capacity in the presence of FCCP when compared to the chow-diet fed control mice. By using a 96-well microplate format, our method provides a flexible and efficient platform to investigate mitochondrial parameters of intact skeletal muscle fibres obtained from adult mice.

Background: Although biochemical markers have been used to monitor training loads (TL), it is unknown if they can be used to predict muscle injuries (MI) in professional football (soccer) players (PFP). Objectives: To evaluate the relationship between the incidence of MI, serum concentration of creatine phosphokinase (CPK) and urea, as well as TL in PFP. Methods: Twenty-three PFP from a Colombian first-division team were enrolled in a retrospective cohort study. CPK, urea, TL and new MI were measured during 19 weeks. CPK and urea serum levels within 4 weeks before a diagnosed MI were compared to those measured preseason. CPK and urea relationship with TL were analyzed using a mixed-effects model. Results: The subjects had an age of 25.3 ± 4.2 years. Nine subjects presented with MI during follow-up, 66.6% of which were localized to hamstrings. Serum CPK and urea profiles were constructed for each player along the season. Injured players had a significant elevation of these markers within 4 weeks before the injury was clinically evident when compared to their own preseason values. Expected individual increases in CPK and urea according to TL during the season were estimated. Conclusions: Since CPK and urea values rose several weeks before the MI became overt, constructing CPK and urea profiles for each player during the whole preseason and season may help identify peaks in their concentration as early markers of MI. A tight biochemical control of training may become a preventive strategy for MI, but the use of published reference values is discouraged.

Pomolic acid (PA) isolated from Licania pittieri has hypotensive effects in rats, inhibits human platelet aggregation and elicits endothelium-dependent relaxation in rat aortic rings. The present study was designed to investigate the effects of PA on cardiomyocytes. Trabeculae and enzymatically isolated cardiomyocytes from rats were used to evaluate the concentration-dependent effects of PA on cardiac muscle tension and excitation-contraction coupling (ECC) by recording Ca2+ transients reported with Fluo-3 and Fura-2, as well as L-type Ca2+ currents (LTCC). PA reduced the contractile force in rat cardiac trabeculae with an EC50 = 14.3 ± 2.4 μM. PA also reduced the amplitude of Ca2+ transients in a concentration-dependent manner, with an EC50 = 10.5 ± 1.3 μM, without reducing sarcoplasmic reticulum (SR) Ca2+ loading. PA decreased the half width of the Ca2+ transient by 31.7 ± 3.3% and increased the decay time and decay time constant (τ) by 7.6 ± 2.7% and 75.6 ± 3.7%, respectively, which was associated with increased phospholamban (PLN) phosphorylation. PA also reversibly reduced the macroscopic LTCC in the cardiomyocyte membrane, but did not demonstrate any effects on skeletal muscle ECC. In conclusion, PA reduces LTCC, Ca2+ transients and cardiomyocyte force, which along with its vasorelaxant effects explain its hypotensive properties. Increased PLN phosphorylation protected the SR from Ca2+ depletion. Considering the effects of PA on platelet aggregation and the cardiovascular system, we propose it as a new potential, multitarget cardiovascular agent with a demonstrated safety profile.

Background Evidence of the efficacy of high-intensity, low-volume interval training (HIIT-low volume) in treating insulin resistance (IR) in patients with metabolic disorders is contradictory. In addition, it is unknown whether this effect is mediated through muscle endocrine function, which in turn depends on muscle mass and fiber type composition. Our aims were to assess the efficacy of HIIT-low volume compared to continuous aerobic exercise (CAE) in treating IR in adults with metabolic syndrome (MS) and to establish whether musclin, apelin, muscle mass and muscle composition are mediators of the effect. Methods This is a controlled, randomized, clinical trial using the minimization method, with blinding of those who will evaluate the outcomes and two parallel groups for the purpose of showing superiority. Sixty patients with MS and IR with ages between 40 and 60 years will be included. A clinical evaluation will be carried out, along with laboratory tests to evaluate IR (homeostatic model assessment (HOMA)), muscle endocrine function (serum levels of musclin and apelin), thigh muscle mass (by dual energy x-ray absorptiometry (DXA) and thigh muscle composition (by carnosine measurement with proton magnetic resonance spectroscopy (1H–MRS)), before and after 12 weeks of a treadmill exercise program three times a week. Participants assigned to the intervention (n = 30) will receive HIIT-low volume in 22-min sessions that will include six intervals at a load of 90% of maximum oxygen consumption (VO2 max) for 1 min followed by 2 min at 50% of VO2 max. The control group (n = 30) will receive CAE at an intensity of 60% of VO2 max for 36 min. A theoretical model based on structural equations will be proposed to estimate the total, direct and indirect effects of training on IR and the proportion explained by the mediators. Discussion Compared with CAE, HIIT-low volume can be effective and efficient at improving physical capacity and decreasing cardiovascular risk factors, such as IR, in patients with metabolic disorders. Studies that evaluate mediating variables of the effect of HIIT-low volume on IR, such as endocrine function and skeletal muscle structure, are necessary to understand the role of skeletal muscle in the pathophysiology of MS and their regulation by exercise. Trial registration NCT03087721. High-intensity Interval, Low Volume Training in Metabolic Syndrome (Intraining-MET). Registered on 22 March 2017, retrospectively registered. Electronic supplementary material The online version of this article (10.1186/s13063-018-2541-7) contains supplementary material, which is available to authorized users.

The skeletal muscle has several types of fibers that differ in structure, metabolism, and function. Fiber types determine the ability of horses to perform in various sports or work activities. Gluteus medius muscles of Colombian creole horses (CCHs) were sampled to determine their fiber types. Samples were processed using myosin adenosine triphosphatase (mATPase) and immunohistochemistry for fiber typing, myofibril electrophoresis for myosin heavy chain composition, and nicotinamide adenine dinucleotide diaphorase activity for oxidative capacity. The following fiber proportions were observed by immunohistochemistry (n = 7): 22.5 ± 3.7% type I, 33.6 ± 2.3% type IIA, 43.6 ± 4.4% type IIX, and 0.3 ± 0.2% hybrid I/IIA fibers. The results obtained by mATPase were comparable. Regarding the oxidative capacity, 20.1 ± 4.0% had a high oxidative reaction, 32.7 ± 6.1% an intermediate reaction, and 47.2 ± 7.4% a low oxidative reaction. Of these, the high and low capacity correlated with type I and IIX fibers, respectively. Myosin heavy chain composition experiments (n = 7) showed 22.2 ± 1.6% of type I, 30.4 ± 2.7% of type IIA, and 47.4 ± 2.3% of type IIX. These values are close to those published for Andalusian horses but differ from some reported for other breeds. Considering the high percentage of type IIX fibers and low to intermediate oxidative capacity, we conclude that the CCH is adapted to perform power exercise and moderate- to high-intensity anaerobic work with short to average duration. Therefore, training should be aimed at increasing aerobic capacity and endurance if these animals are required to perform long-length exercise.

First coined by Alexander Sandow in 1952, the term excitation–contraction coupling (ECC) describes the rapid communication between electrical events occurring in the plasma membrane of skeletal muscle fibres and Ca2+ release from the SR, which leads to contraction. The sequence of events in twitch skeletal muscle involves: (1) initiation and propagation of an action potential along the plasma membrane, (2) spread of the potential throughout the transverse tubule system (T-tubule system), (3) dihydropyridine receptors (DHPR)-mediated detection of changes in membrane potential, (4) allosteric interaction between DHPR and sarcoplasmic reticulum (SR) ryanodine receptors (RyR), (5) release of Ca2+ from the SR and transient increase of Ca2+ concentration in the myoplasm, (6) activation of the myoplasmic Ca2+ buffering system and the contractile apparatus, followed by (7) Ca2+ disappearance from the myoplasm mediated mainly by its reuptake by the SR through the SR Ca2+ adenosine triphosphatase (SERCA), and under several conditions movement to the mitochondria and extrusion by the Na+/Ca2+ exchanger (NCX). In this text, we review the basics of ECC in skeletal muscle and the techniques used to study it. Moreover, we highlight some recent advances and point out gaps in knowledge on particular issues related to ECC such as (1) DHPR-RyR molecular interaction, (2) differences regarding fibre types, (3) its alteration during muscle fatigue, (4) the role of mitochondria and store-operated Ca2+ entry in the general ECC sequence, (5) contractile potentiators, and (6) Ca2+ sparks.

Background: Previous research has demonstrated an association between the metabolic syndrome (MS) and muscle mass; however, no studies have shown any relationship with a particular segment of the body, which would be more useful in clinical settings. Aims: To investigate the association between muscle development of different segments of the body and presence of the MS in adults. Methods: We used fractionation of body mass to calculate the development of muscle mass and correlated this with presence of the MS in a cross-sectional study in adults. Results: The mean age and body mass index were 42.7 ± 6.6 years and 25.3 ± 3.7 kg/m2, respectively. 23.1% of adults suffered from the MS. After adjusting for multiple variables, the Z score of both thigh and chest muscle girths were significantly associated with the MS. There were significant differences between adults with or without the MS in the Z score of thigh [–0.686; 95% confidence interval (95% CI) –1.020 to –0.351], mid-thigh (–0.566; 95% CI –0.931 to –0.200) and chest (0.611; 95% CI 0.260–0.962) girths. Conclusions: There is an association between muscle development and the MS; moreover, muscle thigh perimeter was larger in those without the MS. The use of muscle development of the thigh as an indicator of cardiovascular health-related metabolic alterations is proposed.

We used enzymatically dissociated flexor digitorum brevis (FDB) and soleus fibres loaded with the fast Ca(2+) dye Magfluo-4 AM, and adhered to Laminin, to test whether repetitive stimulation induces progressive changes in the kinetics of Ca(2+) release and reuptake in a fibre-type-dependent fashion. We applied a protocol of tetani of 350 ms, 100 Hz, every 4 s to reach a mean amplitude reduction of 25% of the first peak. Morphology type I (MT-I) and morphology type II (MT-II) fibres underwent a total of 96 and 52.8 tetani (P < 0.01 between groups), respectively. The MT-II fibres (n = 18) showed significant reductions of the amplitude (19%), an increase in rise time (8.5%) and a further reduction of the amplitude/rise time ratio (25.5%) of the first peak of the tetanic transient after 40 tetani, while MT-I fibres (n = 5) did not show any of these changes. However, both fibre types showed significant reductions in the maximum rate of rise of the first peak after 40 tetani. Two subpopulations among the MT-II fibres could be distinguished according to Ca(2+) reuptake changes. Fast-fatigable MT-II fibres (fMT-II) showed an increase of 32.2% in the half-width value of the first peak, while for fatigue-resistant MT-II fibres (rMT-II), the increase amounted to 6.9%, both after 40 tetani. Significant and non-significant increases of 36.4% and 11.9% in the first time constant of decay (t(1)) values were seen after 40 tetani in fMT-II and rMT-II fibres, respectively. MT-I fibres did not show kinetic changes in any of the Ca(2+) reuptake variables. All changes were reversed after an average recovery of 7.5 and 15.4 min for MT-I and MT-II fibres, respectively. Further experiments ruled out the possibility that the differences in the kinetic changes of the first peak of the Ca(2+) transients between fibres MT-I and MT-II could be related to the inactivation of Ca(2+) release mechanism. In conclusion, we established a model of enzymatically dissociated fibres, loaded with Magfluo-4 and adhered to Laminin, to study muscle fatigue and demonstrated fibre-type-dependent, fatigue-induced kinetic changes in both Ca(2+) release and reuptake.

Electrically elicited Ca2+ transients reported with the fast Ca2+ dye MagFluo-4 AM and myosin heavy chain (MHC) electrophoretic patterns were obtained in intact, enzymatically dissociated fibres from adult mice extensor digitorum longus (EDL) and soleus muscles. Thirty nine fibres (23 from soleus and 16 from EDL) were analysed by both fluorescence microscopy and electrophoresis. These fibres were grouped as follows: group 1 included 13 type I and 4 type IC fibres; group 2 included 2 type IIC, 3 IIA and 1 I/IIA/IIX fibres; group 3 included 4 type IIX and 1 type IIX/IIB fibres; group 4 included 2 type IIB/IIX and 9 type IIB fibres. Ca2+ transients obtained in groups 1, 2, 3 and 4 had the following kinetic parameters (mean ±s.e.m.): amplitude (ΔF/F): 0.61 ± 0.05, 0.53 ± 0.08, 0.61 ± 0.06 and 0.61 ± 0.03; rise time (ms): 1.64 ± 0.05, 1.35 ± 0.05, 1.18 ± 0.06 and 1.14 ± 0.04; half-amplitude width (ms): 19.12 ± 1.85, 11.86 ± 3.03, 4.62 ± 0.31 and 4.23 ± 0.37; and time constants of decay (τ1 and τ2, ms): 3.33 ± 0.13 and 52.48 ± 3.93, 2.69 ± 0.22 and 41.06 ± 9.13, 1.74 ± 0.06 and 12.88 ± 1.93, and 1.56 ± 0.11 and 9.45 ± 1.03, respectively. The statistical differences between the four groups and the analysis of the distribution of the parameters of Ca2+ release and clearance show that there is a continuum from slow to fast, that parallels the MHC continuum from pure type I to pure IIB. However, type IIA fibres behave more like IIX and IIB fibres regarding Ca2+ release but closer to type I fibres regarding Ca2+ clearance. In conclusion, we show for the first time the diversity of Ca2+ transients for the whole continuum of fibre types and correlate this functional diversity with the structural and biochemical diversity of the skeletal muscle fibres.

To decide the training for an athlete, it is essential to determine if he/she has a powerful or endurance profile, based on valid and simple measurements. This work describes how to classify athletes as powerful or endurance based on their performance on field physical tests, via clusters analysis, and measures the influence of skeletal muscle fibre type composition and cardiovascular function in such performance. Methods 51 elite athletes (20.6 ± 2.9 years, 30 women) of team sports (25% handball, 22% basketball, 21% volleyball floor, 18% softball, 8% beach volleyball, 6% indoor soccer) were evaluated in Medellin, Colombia, with the following: 1. Performance on field tests: Three jumps -free vertical (FVJ), counter movement (CMJ), and squat (SQT)-; two velocity tests −20 metres dash and shuttle sprint- and ergospirometry (VO2); 2. Noninvasive quantification of intramuscular carnosine (mM/Kg.wt) in vastus lateralis muscle (VLM), a surrogate of area occupied by type II fibres in muscle, by proton magnetic resonance spectroscopy; 3. Cardiac structure and function by echocardiography; 4. Haemodynamic and autonomic response, both at rest and at 70°, by impedance cardiography. Results Clusters determined that best field tests to distinguish between powerful (n = 26, 51%) and endurance (n = 25, 49%) were the three jumps and the 20 metres shuttle sprint. Both groups did not differ in age, sports age or training volume, but body mass index (BMI, Kg/m2) and percentage of body fat (bf%) were lower in powerful than in endurance athletes (p Conclusions The 20 metres velocity is explained essentially by body composition and cardiovascular variables and the jump is explained fundamentally by body composition and muscle composition, which can be accessed by noninvasive spectroscopy. This new methodology associates biochemical intramuscular variables such carnosine with field tests, and helps to evaluate and classify athletes, to control training and to understand variables which determine performance during a competition. (Grant:CODI2565;Colciencias-Coldeportes FP44842-379-2014)

The protein mammalian target of rapamycin (mTOR) is a serine/threonine kinase regulating a number of biochemical pathways controlling cell growth. mTOR exists in two complexes termed mTORC1 and mTORC2. Regulatory associated protein of mTOR (raptor) is associated with mTORC1 and is essential for its function. Ablation of raptor in skeletal muscle results in several phenotypic changes including decreased life expectancy, increased glycogen deposits and alterations of the twitch kinetics of slow fibres. In the present paper, we show that in muscle-specific raptor knockout (RamKO), the bulk of glycogen phosphorylase (GP) is mainly associated in its cAMP-non-stimulated form with sarcoplasmic reticulum (SR) membranes. In addition, 3[H]–ryanodine and 3[H]–PN200-110 equilibrium binding show a ryanodine to dihydropyridine receptors (DHPRs) ratio of 0.79 and 1.35 for wild-type (WT) and raptor KO skeletal muscle membranes respectively. Peak amplitude and time to peak of the global calcium transients evoked by supramaximal field stimulation were not different between WT and raptor KO. However, the increase in the voltage sensor-uncoupled RyRs leads to an increase of both frequency and mass of elementary calcium release events (ECRE) induced by hyper-osmotic shock in flexor digitorum brevis (FDB) fibres from raptor KO. The present study shows that the protein composition and function of the molecular machinery involved in skeletal muscle excitation–contraction (E–C) coupling is affected by mTORC1 signalling.

Background The consumption of beverages containing caffeine and taurine before exercising has been associated with increased physical and psychological performances and has been promoted to support the emotional state and provide vitality to consumers. However, there are contradictory results on these issues, it is not clear the effect of every major compound in relation to the whole effect of the beverages and there is a lack in knowledge about their degree of safety for consumption. Methods This study used a double-blind, placebo controlled, randomized, crossover design. Fourteen male volunteer soldiers from the Colombian army performed different tests to measure their cardiorespiratory fitness (VO2max and maximum heart rate), time to exhaustion, strength (isometric strength), power (vertical jump), concentration (Grid test) and memory (Digits test) after drinking 250 ml of one of the following beverages: one with 80 mg caffeine, one with 1000 mg taurine, one with 80 mg caffeine plus 1000 mg taurine, a commercial energy drink (Red Bull®) or a placebo drink. Subjects were caffeine-consumers that avoided caffeine during the day of evaluation. All beverages were matched in flavor and other organoleptic properties to the commercial one, were bottled in dark plastic bottles and were administered in identical conditions to the participants. Differences between treatments were assessed using repeated measures and analysis of variance. Results The mean ± SD values of VO2max, maximum heart rate, time to exhaustion, right handgrip strength, left handgrip strength, vertical jump, Grid test and Digits test were 61.3 ± 6.2 ml/kg.min, 196 ± 6.8 beats per min, 17 ± 1.2 min, 56.8 ± 6.6 kgf, 53.1 ± 5.9 kgf, 41.1 ± 3.8 cm, 19.9 ± 5.9 observed digits and 10.9 ± 3.1 remembered digits after drinking a placebo drink. Comparisons among the commercial drink, caffeine, taurine, caffeine plus taurine and placebo treatments did not show statistically differences in the results of the performed tests. No adverse effects were reported by the participants. Conclusion The consumption of caffeine (80 mg) and taurine (1000 mg) or their combination does not increase the physical and cognitive ability in young adults during exercise.

The relationship between force and the velocity at which a load can be moved is known as force-velocity (F-V) curve. Methods that control strength training intensity based on F-V curves have been proposed. However, F-V curves available were built for a specific European population. Moreover, those curves need to be revisited since they ignored one factor that strongly affect their kinetics, namely muscle fibre type composition. We propose that F-V curves must consider the functional and metabolic profile of the athletes, and hypothesise that at least two F-V curves with different kinetics can be built. Then, we evaluated whether there are differences in speed during the concentric phase of the deep squat at submaximal loads and also built F-V curves according to the different functional and metabolic profile of the athletes. An analytical, cross-sectional observational study involving 147 elite team sports athletes (basketball, handball, softball, indoor soccer, field soccer, volleyball floor and beach volleyball) was carried out in Medellin, Colombia. All athletes (19.3 ± 3.2 years old, 51.7% men) underwent a medical and anthropometric evaluation, as well as six physical tests: free vertical, counter movement, and squat jumps, 20 metres and fly 20 metres sprint tests and ergospirometry. A cluster analysis that included the results of physical tests allowed us to classify athletes as “powerful” or “endurance”. The speed at submaximal loads (30%, 40%, 50%, 60%, 70% and 80% of maximal load lifted), measured with an isoinertial force transducer during the concentric phase of the deep squat, allowed us to build F-V curves. Moreover, a subsample of 49 athletes (38.8% men) was evaluated by proton resonance magnetic spectroscopy for noninvasive quantification of intramuscular carnosine in their vastus lateralis muscle (VLM), in order to estimate the area occupied by type II fibres. 66 athletes were classified as powerful and were different in body composition and physical tests results compared to endurance athletes (p In conclusion, there are differences in speed during the concentric phase of the deep squat at submaximal loads according to the functional profile of the athletes. This establishes two F-V curves with different kinetics, which consider the fact that powerful athletes have more area of type II fibres in their VLM. These are the first F-V curves built for different types of team sports athletes taking into account their muscle fibre type composition and reconcile sports medicine tests with knowledge obtained from basic sciences studies on skeletal muscle (CODI2565;Colciencias-ColdeportesFP44842-379-2014).

We used enzymatically dissociated flexor digitorum brevis (FDB) and soleus fibres loaded with the fast Ca(2+) dye Magfluo-4 AM, and adhered to Laminin, to test whether repetitive stimulation induces progressive changes in the kinetics of Ca(2+) release and reuptake in a fibre-type-dependent fashion. We applied a protocol of tetani of 350 ms, 100 Hz, every 4 s to reach a mean amplitude reduction of 25% of the first peak. Morphology type I (MT-I) and morphology type II (MT-II) fibres underwent a total of 96 and 52.8 tetani (P0.01 between groups), respectively. The MT-II fibres (n = 18) showed significant reductions of the amplitude (19%), an increase in rise time (8.5%) and a further reduction of the amplitude/rise time ratio (25.5%) of the first peak of the tetanic transient after 40 tetani, while MT-I fibres (n = 5) did not show any of these changes. However, both fibre types showed significant reductions in the maximum rate of rise of the first peak after 40 tetani. Two subpopulations among the MT-II fibres could be distinguished according to Ca(2+) reuptake changes. Fast-fatigable MT-II fibres (fMT-II) showed an increase of 32.2% in the half-width value of the first peak, while for fatigue-resistant MT-II fibres (rMT-II), the increase amounted to 6.9%, both after 40 tetani. Significant and non-significant increases of 36.4% and 11.9% in the first time constant of decay (t(1)) values were seen after 40 tetani in fMT-II and rMT-II fibres, respectively. MT-I fibres did not show kinetic changes in any of the Ca(2+) reuptake variables. All changes were reversed after an average recovery of 7.5 and 15.4 min for MT-I and MT-II fibres, respectively. Further experiments ruled out the possibility that the differences in the kinetic changes of the first peak of the Ca(2+) transients between fibres MT-I and MT-II could be related to the inactivation of Ca(2+) release mechanism. In conclusion, we established a model of enzymatically dissociated fibres, loaded with Magfluo-4 and adhered to Laminin, to study muscle fatigue and demonstrated fibre-type-dependent, fatigue-induced kinetic changes in both Ca(2+) release and reuptake.

We used enzymatically dissociated FDB and Soleus fibers loaded with the fast Ca2+ dye Magfluo-4 AM (Calderon et al. 2010), to test whether repetitive stimulation induces progressive changes in the kinetics of Ca2+ release and reuptake in a fiber type-dependent fashion. Control experiments applying repetitive stimulation to FDB fibers loaded with Fluo-3 AM demonstrated that the preparation reproduced the main previously published findings on Ca2+ transients during fatigue, namely the tetanic Ca2+ transient amplitude decrease and the basal Ca2+ increase (Westerblad & Allen, 1991). When loaded with Magfluo-4 AM, a subgroup of MT-II fibers (fMT-II) showed significant reductions, of 28,1 and 29% (n=7), of the amplitude and the amplitude/rise time relationship of the first peak of the tetanic transient, respectively, after 40 tetani. A subgroup of more resistant MT-II fibers (rMT-II) showed reductions of 21,6 and 28,8% (n=6) only after 60 tetani. MT-I fibers (n=5) showed significant changes in both variables only after 80 tetani. fMT-II fibers also showed an increase of 33,6% in the half width value of the first peak. MT-I fibres did not show kinetic changes in the decay phase of the tetanic transients, while significant changes of 29,3 and 13,3% in the first time constant of decay (t1) values were seen after only 20 tetani in fMT-II and rMT-II fibers, respectively. These changes were reversed after an average recovery period of 10 min. Further experiments ruled out the possibility that the differences in the kinetic changes of Ca2+ release between fibers MT-I and MT-II could be related to the inactivation of Ca2+ release mechanism. In conclusion, we show that a fatiguing protocol induces important kinetic alterations of both Ca2+ release and reuptake, which are larger in fibers MT-II than in fibers MT-I (FONACIT G-2001000637).