Juan C. Calderón

Myosin heavy chain isoform composition and Ca2+ transients in fibres from enzymatically dissociated murine soleus and extensor digitorum longus muscles

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.

The excitation–contraction coupling mechanism in skeletal muscle

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.

Effects of energy drink major bioactive compounds on the performance of young adults in fitness and cognitive tests: a randomized controlled trial

BackgroundThe 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.MethodsThis 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 250íml of one of the following beverages: one with 80ímg caffeine, one with 1000ímg taurine, one with 80ímg caffeine plus 1000ímg taurine, a commercial energy drink (Red Bullí) 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.ResultsThe mean í 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 í 6.2íml/kg.min, 196 í 6.8 beats per min, 17 í 1.2ímin, 56.8 í 6.6íkgf, 53.1 í 5.9íkgf, 41.1 í 3.8ícm, 19.9 í 5.9 observed digits and 10.9 í 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.ConclusionThe consumption of caffeine (80ímg) and taurine (1000ímg) or their combination does not increase the physical and cognitive ability in young adults during exercise.

Association between Thigh Muscle Development and the Metabolic Syndrome in Adults

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.

Kinetic changes in tetanic Ca2+ transients in enzymatically dissociated muscle fibres under repetitive stimulation

Non‐Technical Summary  The transient and progressive decrease in skeletal muscle performance during contraction is known as fatigue. One of the phenomena associated with fatigue is an alteration in the excitation–contraction coupling mechanism. Using isolated muscle fibres loaded with the fast Ca2+ dye Magfluo‐4, we have found that after a protocol of repetitive stimulation there are alterations in the ability of the fibres to release and reuptake Ca2+, which are more evident and rapidly established in fast fibres compared to slow ones. All alterations were reversed after several minutes of rest and were not related to a phenomenon of inactivation of Ca2+ release. These data increase our knowledge of the events present during muscle fatigue and will help understand the mechanisms responsible for them.

Efficacy of high-intensity, low-volume interval training compared to continuous aerobic training on insulin resistance, skeletal muscle structure and function in adults with metabolic syndrome: study protocol for a randomized controlled clinical trial (Intraining-MET)

BackgroundEvidence 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.MethodsThis 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.DiscussionCompared 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 registrationNCT03087721. High-intensity Interval, Low Volume Training in Metabolic Syndrome (Intraining-MET). Registered on 22 March 2017, retrospectively registered.

Development of a high‐throughput method for real‐time assessment of cellular metabolism in intact long skeletal muscle fibre bundles

We developed a method that allows for real‐time assessment of cellular metabolism in isolated, intact long skeletal muscle fibre bundles from adult mice. This method can be used to study changes in mitochondrial function and fuel utilisation in live skeletal muscle fibre bundles. Our method enables flexibility in experimental design and high‐throughput assessment of mitochondrial parameters in isolated skeletal muscle fibre bundles. Extensor digitorum longus (EDL) fibre bundles obtained from chronic high‐fat diet fed mice had lower basal oxygen consumption under FCCP‐induced maximal respiration, when compared to control chow‐fed mice. EDL fibre bundles obtained from chronic high‐fat diet fed mice had enhanced mitochondrial oxidation capacity under FCCP‐induced maximal respiration, when compared to control chow‐fed mice.

O-38 A new method for classifying athletes between powerful and endurance: physiological variables that explain their different performance in field tests

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 < 0,05). ANCOVA adjusted for BMI, bf% and age, showed larger muscular type II fibres area in VLM in powerful than in endurance athletes (38.2% vs. 29.5%; difference between means 8.7%, IC 95%, 4.02–13.3, p = 0.01). The only cardiovascular variable with significant difference was mitral valve E/A ratio, lower in powerful compared to endurance (1.9 vs 2.4; difference between means 0.5, IC 95%, −0.1 to −0.9, p < 0.05), suggesting better diastolic function and less cardiac rigidity in the latter. In multiple linear regression analysis, introducing demography, anthropometry, cardiac structure and function, and intramuscular mM/Kg.wt of carnosine, the variability of 20 metres sprints was explained (R2 = 0.82, p < 0.05 for all cases) by bf% (ß coefficient −0.6, meaning that for each 1% rise in body fat, velocity reduces 0.6 m/s), left ventricle diastolic diameter index (ß 0.47, for each cm/m2 rise in diameter, velocity raises 0.47 m/sec), cardiac index at 70° (ß 0.9) and contractility index at 70° (ß −0.04). The variability of jumps was explained (R2 = 0.78) by bf% (ß −0.84 for CMJ) and carnosine (ß 1.9 for CMJ, which means that each 1 mM/Kg.wt rise in carnosine raises 1.9 cm the CMJ). 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)

O-39 Force-velocity curves for powerful and endurance athletes: effect of muscle fibre type composition

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 Medellín, 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 < 0.01). A multivariate model adjusted for age, sex, body mass index (BMI) and body fat percentage, showed significantly higher values in powerful vs. endurance athletes in maximal load (15.6%), velocities at all submaximal loads (5.6%), load values (15.9%), and maximal power (20.5%), giving F-V curves with different kinetics between both groups of athletes. After adjusting for age, BMI and body fat percentage, the carnosine concentration in VLM was higher in powerful athletes (4.5 ± 0.2 mM/Kg.wt, n = 26) than in endurance ones (3.6 ± 0.2 mM/Kg.wt, n = 23; P < 0.01). This corresponded to a higher (P < 0.01) area occupied by fibres type II in powerful (38.2 ± 1.6%) than endurance (29.5 ± 1.4%) athletes. 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).