Showing papers in "European Journal of Applied Physiology in 2020"

Physiological mechanisms determining eccrine sweat composition.

Abstract: The purpose of this paper is to review the physiological mechanisms determining eccrine sweat composition to assess the utility of sweat as a proxy for blood or as a potential biomarker of human health or nutritional/physiological status. This narrative review includes the major sweat electrolytes (sodium, chloride, and potassium), other micronutrients (e.g., calcium, magnesium, iron, copper, zinc, vitamins), metabolites (e.g., glucose, lactate, ammonia, urea, bicarbonate, amino acids, ethanol), and other compounds (e.g., cytokines and cortisol). Ion membrane transport mechanisms for sodium and chloride are well established, but the mechanisms of secretion and/or reabsorption for most other sweat solutes are still equivocal. Correlations between sweat and blood have not been established for most constituents, with perhaps the exception of ethanol. With respect to sweat diagnostics, it is well accepted that elevated sweat sodium and chloride is a useful screening tool for cystic fibrosis. However, sweat electrolyte concentrations are not predictive of hydration status or sweating rate. Sweat metabolite concentrations are not a reliable biomarker for exercise intensity or other physiological stressors. To date, glucose, cytokine, and cortisol research is too limited to suggest that sweat is a useful surrogate for blood. Final sweat composition is not only influenced by extracellular solute concentrations, but also mechanisms of secretion and/or reabsorption, sweat flow rate, byproducts of sweat gland metabolism, skin surface contamination, and sebum secretions, among other factors related to methodology. Future research that accounts for these confounding factors is needed to address the existing gaps in the literature.

The energy cost of swimming and its determinants

Abstract: The energy expended to transport the body over a given distance (C, the energy cost) increases with speed both on land and in water. At any given speed, C is lower on land (e.g., running or cycling) than in water (e.g., swimming or kayaking) and this difference can be easily understood when one considers that energy should be expended (among the others) to overcome resistive forces since these, at any given speed, are far larger in water (hydrodynamic resistance, drag) than on land (aerodynamic resistance). Another reason for the differences in C between water and land locomotion is the lower capability to exert useful forces in water than on land (e.g., a lower propelling efficiency in the former case). These two parameters (drag and efficiency) not only can explain the differences in C between land and water locomotion but can also explain the differences in C within a given form of locomotion (swimming at the surface, which is the topic of this review): e.g., differences between strokes or between swimmers of different age, sex, and technical level. In this review, the determinants of C (drag and efficiency, as well as energy expenditure in its aerobic and anaerobic components) will, thus, be described and discussed. In aquatic locomotion it is difficult to obtain quantitative measures of drag and efficiency and only a comprehensive (biophysical) approach could allow to understand which estimates are "reasonable" and which are not. Examples of these calculations are also reported and discussed.

SPEXOR passive spinal exoskeleton decreases metabolic cost during symmetric repetitive lifting

Abstract: Besides mechanical loading of the back, physiological strain is an important risk factor for low-back pain. Recently a passive exoskeleton (SPEXOR) has been developed to reduce loading on the low back. We aimed to assess the effect of this device on metabolic cost of repetitive lifting. To explain potential effects, we assessed kinematics, mechanical joint work, and back muscle activity. We recruited ten male employees, working in the luggage handling department of an airline company and having ample experience with lifting tasks at work. Metabolic cost, kinematics, mechanical joint work and muscle activity were measured during a 5-min repetitive lifting task. Participants had to lift and lower a box of 10 kg from ankle height with and without the exoskeleton. Metabolic cost was significantly reduced by 18% when wearing the exoskeleton. Kinematics did not change significantly, while muscle activity decreased by up to 16%. The exoskeleton took over 18–25% of joint work at the hip and L5S1 joints. However, due to large variation in individual responses, we did not find a significant reduction of joint work around the individual joints. Wearing the SPEXOR exoskeleton decreased metabolic cost and might, therefore, reduce fatigue development and contribute to prevention of low-back pain during repetitive lifting tasks. Reduced metabolic cost can be explained by the exoskeleton substituting part of muscle work at the hip and L5S1 joints and consequently decreasing required back muscle activity.

Nutritional interventions for reducing the signs and symptoms of exercise-induced muscle damage and accelerate recovery in athletes: current knowledge, practical application and future perspectives

Abstract: This review provides an overview of the current knowledge of the nutritional strategies to treat the signs and symptoms related to EIMD. These strategies have been organized into the following sections based upon the quality and quantity of the scientific support available: (1) interventions with a good level of evidence; (2) interventions with some evidence and require more research; and (3) potential nutritional interventions with little to-no-evidence to support efficacy. Pubmed, EMBASE, Scopus and Web of Science were used. The search terms ‘EIMD’ and ‘exercise-induced muscle damage’ were individually concatenated with ‘supplementation’, ‘athletes’, ‘recovery’, ‘adaptation’, ‘nutritional strategies’, hormesis’. Supplementation with tart cherries, beetroot, pomegranate, creatine monohydrate and vitamin D appear to provide a prophylactic effect in reducing EIMD. β-hydroxy β-methylbutyrate, and the ingestion of protein, BCAA and milk could represent promising strategies to manage EIMD. Other nutritional interventions were identified but offered limited effect in the treatment of EIMD; however, inconsistencies in the dose and frequency of interventions might account for the lack of consensus regarding their efficacy. There are clearly varying levels of evidence and practitioners should be mindful to refer to this evidence-base when prescribing to clients and athletes. One concern is the potential for these interventions to interfere with the exercise-recovery-adaptation continuum. Whilst there is no evidence that these interventions will blunt adaptation, it seems pragmatic to use a periodised approach to administering these strategies until data are in place to provide and evidence base on any interference effect on adaptation.

Molecular mechanisms involved in the positive effects of physical activity on coping with COVID-19.

Abstract: Physical activity (PA) represents the first line of defence against diseases characterised by increased inflammation status, such as metabolic and infectious diseases. Conversely, a sedentary lifestyle—associated with obesity, type 2 diabetes and cardiovascular disorders—negatively impacts on general health status, including susceptibility to infections. At a time of a pandemic SARS-CoV2 infection, and in the context of the multiorgan crosstalk (widely accepted as a mechanism participating in the pathophysiology of all organs and systems), we examine the complex interplay mediated by skeletal muscle contraction involving the immune system and how this contributes to control health status and to counteract viral infections. In so doing, we review the molecular mechanisms and expression of molecules modulated by PA, able to provide the proper molecular equipment against viral infections such as the current SARS-CoV2. A critical review of the literature was performed to elucidate the molecular mechanisms and mediators induced by PA that potentially impact on viral infections such as SARS-CoV2. We showed the effects mediated by regular moderate PA on viral adverse effects through the regulation of biological processes involving the crosstalk between skeletal muscle, the immune system and adipose tissue. Evidence was provided of the effects mediated by modulation of the expression of inflammation markers. A tigth association between PA and reduction in inflammation status allows effective counteracting of SARS-CoV2 infection. It is therefore essential to persuade people to keep active.

Effects of green tea extract supplementation and endurance training on irisin, pro-inflammatory cytokines, and adiponectin concentrations in overweight middle-aged men

Abstract: Green tea extract (GTE) supplementation has been proposed to possess anti-inflammatory properties. This study assessed the effects of GTE on endurance training (ET) induced changes on irisin, pro-inflammatory cytokines, adiponectin and anthropometric indices in overweight middle-aged males. Participants were randomly assigned to three groups (n = 15): endurance training + placebo (ET + P), endurance training + green tea extract supplementation (ET + GTE), and no endurance training + placebo (P). The ET intervention consisted of an 8-week training program that included circuit training, fast walking or jogging performed three times/week at a moderate intensity (40–59% of the heart rate reserve). Participants received 500 mg/day GTE using a green tea capsule. Serum concentrations of interleukin 6 (IL-6), tumor necrosis factor-alpha (TNF-α), irisin, adiponectin, and high-sensitivity C-reactive protein (hs-CRP) were measured prior to and after the 8-week training intervention. Both exercise interventions decreased IL-6 and hs-CRP (p < 0.05), and increased adiponectin (p < 0.01) levels; changes in these variables were greater in the ET + GTE group compared to the ET + P and P groups (p < 0.01). Irisin concentrations increased only in the ET + GTE group and were different from the ET + P and P groups (p < 0.01). There were no changes in TNF-α concentrations in any of the groups. Both exercise interventions (ET + GTE and ET + P) decreased bodyweight, body mass index (BMI), body fat percentage (BFP), and visceral fat area (VFA) (p < 0.05), with greater changes in these variables occurring in the ET + GTE group compared to ET + P and P groups (p < 0.01). The combination of GTE supplementation and ET produces beneficial anti-inflammatory and metabolic effects, which were greater than those produced by ET alone.

Effects of exercise and whey protein on muscle mass, fat mass, myoelectrical muscle fatigue and health-related quality of life in older adults: a secondary analysis of the Liverpool Hope University—Sarcopenia Ageing Trial (LHU-SAT)

Abstract: To investigate the effects of exercise in combination with, or without, a leucine-enriched whey protein supplement on muscle mass, fat mass, myoelectrical muscle fatigue and health-related quality of life (HR-QOL) in older adults. 100 community-dwelling older adults [52% women, age: 69 ± 6 years (mean ± SD)] were randomised to four [Control (C); Exercise (E); Exercise + Protein (EP); Protein (P)] independent groups. E and EP groups completed 16 weeks of exercise [resistance (2 times/week) and functional (1 time/week]. EP and P groups were also administered a leucine-enriched whey protein supplement (3 times/day) based on body weight (1.5 g/kg/day). Muscle and fat mass (bioelectrical impedance analysis), myoelectrical muscle fatigue (surface electromyography) and HR-QOL (WHOQOL-BREF) were measured pre- and post-intervention. At post-intervention, the rectus femoris (E: − 4.8%/min, p = 0.007, ES = 0.86; EP: − 3.3%/min, p = 0.045, ES = 0.58) and bicep femoris (E: − 3.9%/min, p 0.05). Physical exercise is a potent method to improve myoelectrical muscle fatigue and HR-QOL in older adults. However, leucine-enriched whey protein did not augment this response in those already consuming sufficient quantities of protein at trial enrolment.

Historical reviews of the assessment of human cardiovascular function: interrogation and understanding of the control of skin blood flow

Abstract: Several techniques exist for the determination of skin blood flow that have historically been used in the investigation of thermoregulatory control of skin blood flow, and more recently, in clinical assessments or as an index of global vascular function. Skin blood flow measurement techniques differ in their methodology and their strengths and limitations. To examine the historical development of techniques for assessing skin blood flow by describing the origin, basic principles, and important aspects of each procedure and to provide recommendations for best practise. Venous occlusion plethysmography was one of the earliest techniques to intermittently index a limb's skin blood flow under conditions in which local muscle blood flow does not change. The introduction of laser Doppler flowmetry provided a method that continuously records an index of skin blood flow (red cell flux) (albeit from a relatively small skin area) that requires normalisation due to high site-to-site variability. The subsequent development of laser Doppler and laser speckle imaging techniques allows the mapping of skin blood flow from larger surface areas and the visualisation of capillary filling from the dermal plexus in two dimensions. The use of iontophoresis or intradermal microdialysis in conjunction with laser Doppler methods allows for the local delivery of pharmacological agents to interrogate the local and neural control of skin blood flow. The recent development of optical coherence tomography promises further advances in assessment of the skin circulation via three-dimensional imaging of the skin microvasculature for quantification of vessel diameter and vessel recruitment.

Peripheral fatigue: new mechanistic insights from recent technologies.

Abstract: Peripheral fatigue results from multiple electrochemical and mechanical events in the cell body and the muscle–tendon complex. Combined force and surface electromyographic signal analysis is among the most widely used approaches to describe the behaviour of a fatigued muscle. Advances in technologies and methodological procedures (e.g. laser diffraction, 31P magnetic resonance spectroscopy, shear-wave elastography, tensiomyography, myotonometry, mechanomyography, and high-density surface electromyography) have expanded our knowledge of muscle behaviour before, during, and after a fatiguing task. This review gives an update on recent developments in technologies for investigating the effects of peripheral fatigue linked to skeletal muscle contraction and on mechanistic insights into the electrochemical and mechanical aspects of fatigue. The salient points from the literature analysis are: (1) the electrochemical and mechanical events in the cell (alterations in cross-bridge formation and function and in depolarization of the tubular membrane) precede the events taking place at the muscle–tendon complex (decrease in muscle–tendon unit stiffness); (2) the changes in the fatigued muscle are not homogenous along its length and width but rather reflect a functional compartmentalisation that counteracts the decline in performance; (3) fatigue induces changes in load sharing among adjacent/synergistic muscles. A focus of future studies is to observe how these regional differences occur within single muscle fibres. To do this, a combination of different approaches may yield new insights into the mechanisms underlying muscle fatigue and how the muscle counteracts fatigue.

Eight weeks of resistance training increases strength, muscle cross-sectional area and motor unit size, but does not alter firing rates in the vastus lateralis.

Abstract: Previous investigations analyzing resistance training’s influence on motor unit (MU) firing rates have yielded mixed results. These mixed results may be clarified by concurrently measuring changes in MU size. Thus, this study analyzed whether post-training strength gains were due to increases in MU firing rates and/or sizes as measured indirectly via action potential amplitudes. Sixteen males (age = 20.7 ± 1.9 years) completed 8 weeks of resistance training, while eight males (age = 19.4 ± 2.5 years) served as controls. Vastus lateralis surface electromyography signals collected during submaximal isometric knee extensions were decomposed to yield an action potential amplitude (MUAPAMP), mean firing rate (MFR), and recruitment threshold (RT) for each MU. Each contraction’s average MFR and MUAPAMP, and coefficients of the linear (y-intercept and slope) MUAPAMP-RT, linear MFR-RT and exponential (A and B terms) MFR–MUAPAMP relationships were analyzed. Firing instances and action potentials were validated via reconstruct-and-test and spike-triggered averaging procedures. Vastus lateralis cross-sectional area (CSA) was analyzed with ultrasonography. Resistance training increased isometric strength from 204.6 ± 34.9 to 239.8 ± 36.3 Nm and vastus lateralis CSA from 28.7 ± 4.7 to 34.0 ± 5.0 cm2. Resistance training did not affect MFR–RT relationship parameters or average MFRs but did increase the slopes of the MUAPAMP–RT relationships (0.0067 ± 0.0041 to 0.0097 ± 0.0045 mV/%MVC) and average MUAPAMPs from 0.189 ± 0.093 to 0.249 ± 0.127 mV. MU hypertrophy altered the MFR–MUAPAMP relationships (B terms: − 3.63 ± 1.40 to − 2.66 ± 1.38 pps/mV). Resistance training induced MU and muscle hypertrophy, but did not alter firing rates. Greater MU twitch forces resulting from larger MUs firing at pre-training rates likely explain resistance training strength gains.

The association of HFE gene H63D polymorphism with endurance athlete status and aerobic capacity: novel findings and a meta-analysis

Abstract: Iron is an important component of the oxygen-binding proteins and may be critical to optimal athletic performance. Previous studies have suggested that the G allele of C/G rare variant (rs1799945), which causes H63D amino acid replacement, in the HFE is associated with elevated iron indexes and may give some advantage in endurance-oriented sports. The aim of the present study was to investigate the association between the HFE H63D polymorphism and elite endurance athlete status in Japanese and Russian populations, aerobic capacity and to perform a meta-analysis using current findings and three previous studies. The study involved 315 international-level endurance athletes (255 Russian and 60 Japanese) and 809 healthy controls (405 Russian and 404 Japanese). Genotyping was performed using micro-array analysis or by PCR. VO2max in 46 male Russian endurance athletes was determined using gas analysis system. The frequency of the iron-increasing CG/GG genotypes was significantly higher in Russian (38.0 vs 24.9%; OR 1.85, P = 0.0003) and Japanese (13.3 vs 5.0%; OR 2.95, P = 0.011) endurance athletes compared to ethnically matched controls. The meta-analysis using five cohorts (two French, Japanese, Spanish, and Russian; 586 athletes and 1416 controls) showed significant prevalence of the CG/GG genotypes in endurance athletes compared to controls (OR 1.96, 95% CI 1.58–2.45; P = 1.7 × 10–9). Furthermore, the HFE G allele was associated with high VO2max in male athletes [CC: 61.8 (6.1), CG/GG: 66.3 (7.8) ml/min/kg; P = 0.036]. We have shown that the HFE H63D polymorphism is strongly associated with elite endurance athlete status, regardless ethnicities and aerobic capacity in Russian athletes.

Exceeding a “critical” muscle Pi: implications for $$\dot{\text{V}}\text{O}_{2}$$ and metabolite slow components, muscle fatigue and the power–duration relationship

Abstract: The consequences of the assumption that the additional ATP usage, underlying the slow component of oxygen consumption ( $$\dot{\text{V}}\text{O}_{2}$$ ) and metabolite on-kinetics, starts when cytosolic inorganic phosphate (Pi) exceeds a certain “critical” Pi concentration, and muscle work terminates because of fatigue when Pi exceeds a certain, higher, “peak” Pi concentration are investigated. A previously developed computer model of the myocyte bioenergetic system is used. Simulated time courses of muscle $$\dot{\text{V}}\text{O}_{2}$$ , cytosolic ADP, pH, PCr and Pi at various ATP usage activities agreed well with experimental data. Computer simulations resulted in a hyperbolic power–duration relationship, with critical power (CP) as an asymptote. CP was increased, and phase II $$\dot{\text{V}}\text{O}_{2}$$ on-kinetics was accelerated, by progressive increase in oxygen tension (hyperoxia). Pi is a major factor responsible for the slow component of the $$\dot{\text{V}}\text{O}_{2}$$ and metabolite on-kinetics, fatigue-related muscle work termination and hyperbolic power–duration relationship. The successful generation of experimental system properties suggests that the additional ATP usage, underlying the slow component, indeed starts when cytosolic Pi exceeds a “critical” Pi concentration, and muscle work terminates when Pi exceeds a “peak” Pi concentration. The contribution of other factors, such as cytosolic acidification, or glycogen depletion and central fatigue should not be excluded. Thus, a detailed quantitative unifying mechanism underlying various phenomena related to skeletal muscle fatigue and exercise tolerance is offered that was absent in the literature. This mechanism is driven by reciprocal stimulation of Pi increase and additional ATP usage when “critical” Pi is exceeded.

The impact of acute and chronic exercise on Nrf2 expression in relation to markers of mitochondrial biogenesis in human skeletal muscle

Abstract: To examine the relationship between changes in nuclear factor erythroid 2-related factor 2 (Nrf2) expression and markers of mitochondrial biogenesis in acutely and chronically exercised human skeletal muscle. The impact of acute submaximal endurance (END) and supramaximal interval (Tabata) cycling on the upregulation of Nrf2 (and its downstream targets), nuclear respiratory factor-1 (NRF-1) and mitochondrial transcription factor A (TFAM) mRNA expression was examined in healthy young males (n = 10). The relationship between changes in citrate synthase (CS) maximal activity and the protein content of Nrf2, heme oxygenase 1 (HO-1), NRF-1, and TFAM was also investigated following 4 weeks of Tabata in a separate group of males (n = 21). Nrf2, NRF-1, and HO-1 mRNA expression increased after acute exercise (p < 0.05), whereas the increase in superoxide dismutase 2 (SOD2) mRNA expression approached significance (p = 0.08). Four weeks of Tabata increased CS activity and Nrf2, NRF-1, and TFAM protein content (p < 0.05), but decreased HO-1 protein content (p < 0.05). Training-induced changes in Nrf2 protein were strongly correlated with NRF-1 (r = 0.63, p < 0.01). When comparing protein content changes between individuals with the largest (HI: + 23%) and smallest (LO: − 1%) observed changes in CS activity (n = 8 each), increases in Nrf2 and TFAM protein content were apparent in the HI group only (p < 0.02) with medium-to-large effect sizes for between-group differences in changes in Nrf2 (ηp2=0.15) and TFAM (ηp2 = 0.12) protein content. Altogether, our findings support a potential role for Nrf2 in exercise-induced mitochondrial biogenesis in human skeletal muscle.

Hypoxic training improves blood pressure, nitric oxide and hypoxia-inducible factor-1 alpha in hypertensive patients

Abstract: To examine the effects of intermittent hypoxic breathing at rest (IHR) or during exercise (IHT) on blood pressure and nitric oxide metabolites (NOx) and hypoxia-inducible factor-1 alpha levels (HIF-1α) over a 6-week period. 47 hypertensive patients were randomly allocated to three groups: hypertensive control (CON: n = 17; IHR: n = 15 and IHT: n = 15. The CON received no intervention; whereas, IH groups received eight events of hypoxia (FIO2 0.14), and normoxia (FIO2 0.21), 24-min hypoxia and 24-min normoxia, for 6 weeks. The baseline data were collected 2 days before the intervention; while, the post-test data were collected at days 2 and 28 after the 6-week intervention. We observed a significant decrease of the SBP in both IH groups: IHR (− 12.0 ± 8.0 mmHg, p = 0.004 and − 9.9 ± 8.8 mmHg, p = 0.028, mean ± 95% CI) and IHT (− 13.0 ± 7.8 mmHg, p = 0.002 and − 10.0 ± 8.4 mmHg, p = 0.016) at days 2 and 28 post-intervention, respectively. Compared to CON, IHR and IHT had increased of NOx (IHR; 8.5 ± 7.6 μmol/L, p = 0.031 and IHT; 20.0 ± 9.1 μmol/L, p < 0.001) and HIF-1α (IHR; 170.0 ± 100.0 pg/mL, p = 0.002 and IHT; 340.5 ± 160.0 pg/mL, p < 0.001). At 2 days post-intervention, NOx and HIF-1α were negatively correlated with SBP in IHT. IH programs may act as an alternative therapeutic strategy for hypertension patients probably through elevation of NOx and HIF-1α production.

Anodal transcranial direct current stimulation enhances strength training volume but not the force-velocity profile

Abstract: This study aimed to explore the acute effect of transcranial direct current stimulation (tDCS) on the force–velocity relationship, strength training volume, movement velocity, and ratings of perceived exertion. Fourteen healthy men (age 22.8 ± 3.0 years) were randomly stimulated over the dorsolateral prefrontal cortex with either ANODAL, CATHODAL or SHAM tDCS for 15 min at 2 mA. The one-repetition maximum (1RM) and force–velocity relationship parameters were evaluated during the bench press exercise before and after receiving the tDCS. Subsequently, participants completed a resistance training session consisting of sets of five repetitions with 1 min of inter-set rest against the 75%1RM until failure. No significant changes were observed in the 1RM or in the force–velocity relationship parameters (p ≥ 0.377). The number of repetitions was higher for the ANODAL compared to the CATHODAL (p = 0.025; ES = 0.37) and SHAM (p = 0.009; ES = 0.47) conditions. The reductions of movement velocity across sets were lower for the ANODAL than for the CATHODAL and SHAM condition (p = 0.014). RPE values were lower for the ANODAL compared to the CATHODAL (p = 0.119; ES = 0.33) and SHAM (p = 0.150; ES = 0.44) conditions. No significant differences between the CATHODAL and SHAM conditions were observed for any variable. The application of ANODAL tDCS before a resistance training session increased training volume, enabled the maintenance of higher movement velocities, and reduced RPE values. These results suggest that tDCS could be an effective method to enhance resistance-training performance.

The effect of caffeine on cognitive performance is influenced by CYP1A2 but not ADORA2A genotype, yet neither genotype affects exercise performance in healthy adults.

Abstract: To determine the influence of two commonly occurring genetic polymorphisms on exercise, cognitive performance, and caffeine metabolism, after caffeine ingestion. Eighteen adults received caffeine or placebo (3 mg kg−1) in a randomised crossover study, with measures of endurance exercise (15-min cycling time trial; 70-min post-supplementation) and cognitive performance (psychomotor vigilance test; PVT; pre, 50 and 95-min post-supplementation). Serum caffeine and paraxanthine were measured (pre, 30 and 120-min post-supplementation), and polymorphisms in ADORA2A (rs5751876) and CYP1A2 (rs762551) genes analysed. Caffeine enhanced exercise performance (P 0.05). Caffeine enhanced PVT performance (P 0.05). Serum caffeine and paraxanthine responses were not different between genotypes (P > 0.05). Caffeine enhanced CYP1A2 ‘fast’ metabolisers’ cognitive performance more than ‘slow’ metabolisers. No other between-genotype differences emerged for the effect of caffeine on exercise or cognitive performance, or metabolism.

MitoQ and CoQ10 supplementation mildly suppresses skeletal muscle mitochondrial hydrogen peroxide levels without impacting mitochondrial function in middle-aged men.

Abstract: Excess production of reactive oxygen species (ROS) from the mitochondria can promote mitochondrial dysfunction and has been implicated in the development of a range of chronic diseases. As such there is interest in whether mitochondrial-targeted antioxidant supplementation can attenuate mitochondrial-associated oxidative stress. We investigated the effect of MitoQ and CoQ10 supplementation on oxidative stress and skeletal muscle mitochondrial ROS levels and function in healthy middle-aged men. Skeletal muscle and blood samples were collected from twenty men (50 ± 1 y) before and following six weeks of daily supplementation with MitoQ (20 mg) or CoQ10 (200 mg). High-resolution respirometry was used to determine mitochondrial respiration and H2O2 levels, markers of mitochondrial mass and antioxidant defences were measured in muscle samples and oxidative stress markers in urine and blood samples. Both MitoQ and CoQ10 supplementation suppressed mitochondrial net H2O2 levels during leak respiration, while MitoQ also elevated muscle catalase expression. However, neither supplement altered urine F2-isoprostanes nor plasma TBARS levels. Neither MitoQ nor CoQ10 supplementation had a significant impact on mitochondrial respiration or mitochondrial density markers (citrate synthase, mtDNA/nDNA, PPARGC1A, OXPHOS expression). Our results suggest that neither MitoQ and CoQ10 supplements impact mitochondrial function, but both can mildly suppress mitochondrial ROS levels in healthy middle-aged men, with some indication that MitoQ may be more effective than CoQ10.

Factors influencing bilateral deficit and inter-limb asymmetry of maximal and explosive strength: motor task, outcome measure and muscle group.

Abstract: The purpose of the present study was to investigate the influence of strength outcome [maximal voluntary contraction (MVC) torque vs. rate of torque development (RTD)], motor task (unilateral vs. bilateral) and muscle group (knee extensors vs. flexors) on the magnitude of bilateral deficits and inter-limb asymmetries in a large heterogeneous group of athletes. 259 professional/semi-professional athletes from different sports (86 women aged 21 ± 6 years and 173 men aged 20 ± 5 years) performed unilateral and bilateral “fast and hard” isometric maximal voluntary contractions of the knee extensors and flexors on a double-sensor dynamometer. Inter-limb asymmetries and bilateral deficits were compared across strength outcomes (MVC torque and multiple RTD measures), motor tasks and muscle groups. Most RTD outcomes showed greater bilateral deficits than MVC torque for knee extensors, but not for knee flexors. Most RTD outcomes, not MVC torque, showed higher bilateral deficits for knee extensors compared to knee flexors. For both muscle groups, all RTD measures resulted in higher inter-limb asymmetries than MVC torque, and most RTD measures resulted in greater inter-limb asymmetries during unilateral compared to bilateral motor tasks. The results of the present study highlight the importance of outcome measure, motor task and muscle group when assessing bilateral deficits and inter-limb asymmetries of maximal and explosive strength. Compared to MVC torque and bilateral tasks, RTD measures and unilateral tasks could be considered more sensitive for the assessment of bilateral deficits and inter-limb asymmetries in healthy professional/semi-professional athletes.

Comparison between high- and low-intensity eccentric cycling of equal mechanical work for muscle damage and the repeated bout effect

Abstract: We compared high- and low-intensity eccentric cycling (ECC) with the same mechanical work for changes in muscle function and muscle soreness, and examined the changes after subsequent high-intensity ECC. Twenty men performed either high-intensity ECC (1 min × 5 at 20% of peak power output: PPO) for two bouts separated by 2 weeks (H–H, n = 11), or low-intensity (4 min × 5 at 5% PPO) for the first and high-intensity ECC for the second bout (L–H, n = 9). Changes in indirect muscle damage markers were compared between groups and bouts. At 24 h after the first bout, both groups showed similar decreases in maximal isometric (70° knee angle, − 10.6 ± 11.8%) and isokinetic ( − 11.0 ± 8.2%) contraction torque of the knee extensors (KE), squat ( − 7.7 ± 10.4%) and counter-movement jump ( − 5.9 ± 8.4%) heights (p < 0.05). Changes in KE torque and jump height were smaller after the second than the first bout for both the groups (p < 0.05). Increases in plasma creatine kinase activity were small, and no significant changes in vastus lateralis or intermedius thickness nor ultrasound echo-intensity were observed. KE soreness with palpation was greater (p < 0.01) in H–H (peak: 4.2 ± 1.0) than L–H (1.4 ± 0.6) after the first bout, but greater in L–H (3.6 ± 0.9) than H–H (1.5 ± 0.5) after the second bout. This was also found for muscle soreness with squat, KE stretch and gluteal palpation. The high- and low-intensity ECC with matched mechanical work induced similar decreases in muscle function, but DOMS was greater after high-intensity ECC, which may be due to greater extracellular matrix damage and inflammation.

Age-related changes in muscle thickness and echo intensity of trunk muscles in healthy women: comparison of 20–60s age groups

Abstract: The objective of this study was to investigate the age-related changes in muscle thickness and muscle echo intensity of trunk in subjects including wide range of age groups. The subjects were 112 healthy women (age range 20–60s). The rectus abdominis, external oblique, internal oblique, transversus abdominis, erector spinae, and lumbar multifidus muscles were examined. To confirm the differences among the age groups, the linear mixed effect models were performed. There were significant decreases in muscle thickness of the rectus abdominis and external oblique muscles in the 50s and 60s age groups compared to those in the 20s age group, and a significant decrease in muscle thickness of the erector spinae muscle in the 60s age group compared to those in the 20s age group. However, there was no significant difference among the age groups in muscle thickness of other trunk muscles. There were significant increases in echo intensity of the abdominal muscles in other age groups compared to those in the 20s age group, and significant increases in echo intensity of the back muscles in the age groups over 40 compared to those in the 20s group. Our study revealed that muscle quality may be more affected by age than muscle quantity and the effects of aging differ among muscles.

Spleen contraction elevates hemoglobin concentration at high altitude during rest and exercise.

Abstract: Hypoxia and exercise are known to separately trigger spleen contraction, leading to release of stored erythrocytes. We studied spleen volume and hemoglobin concentration (Hb) during rest and exercise at three altitudes. Eleven healthy lowlanders did a 5-min modified Harvard step test at 1370, 3700 and 4200 m altitude. Spleen volume was measured via ultrasonic imaging and capillary Hb with Hemocue during rest and after the step test, and arterial oxygen saturation (SaO2), heart rate (HR), expiratory CO2 (ETCO2) and respiratory rate (RR) across the test. Resting spleen volume was reduced with increasing altitude and further reduced with exercise at all altitudes. Mean (SE) baseline spleen volume at 1370 m was 252 (20) mL and after exercise, it was 199 (15) mL (P < 0.01). At 3700 m, baseline spleen volume was 231 (22) mL and after exercise 166 (12) mL (P < 0.05). At 4200 m baseline volume was 210 (23) mL and after exercise 172 (20) mL (P < 0.05). After 10 min, spleen volume increased to baseline at all altitudes (NS). Baseline Hb increased with altitude from 138.9 (6.1) g/L at 1370 m, to 141.2 (4.1) at 3700 m and 152.4 (4.0) at 4200 m (P < 0.01). At all altitudes Hb increased from baseline during exercise to 146.8 (5.7) g/L at 1370 m, 150.4 (3.8) g/L at 3700 m and 157.3 (3.8) g/L at 4200 m (all P < 0.05 from baseline). Hb had returned to baseline after 10 min rest at all altitudes (NS). The spleen-derived Hb elevation during exercise was smaller at 4200 m compared to 3700 m (P < 0.05). Cardiorespiratory variables were also affected by altitude during both rest and exercise. The spleen contracts and mobilizes stored red blood cells during rest at high altitude and contracts further during exercise, to increase oxygen delivery to tissues during acute hypoxia. The attenuated Hb response to exercise at the highest altitude is likely due to the greater recruitment of the spleen reserve during rest, and that maximal spleen contraction is reached with exercise.

Intra-limb and muscular coordination during walking on slopes

Abstract: Intra-limb and muscular coordination during gait are the result of the organisation of the neuromuscular system, which have been widely studied on a flat terrain. Environmental factors, such as the inclination of the terrain, is a challenge for the postural control system to maintain balance. Therefore, we hypothesised that the central nervous system flexibly modifies its control strategies during locomotion on slopes. Ten subjects walked on an inclined treadmill at different slopes (from − 9° to + 9°) and speeds (from 0.56 to 2.22 m s−1). Intra-limb coordination was investigated via the Continuous Relative Phase, whereas muscular coordination was investigated by decomposing the coordinated muscle activation profiles into Basic Activation Patterns. A greater stride to stride variability of kinematics was observed during walking on slopes, as compared to walking on the level. On positive slopes, the stride period and width present a greater variability without modification of the time-pattern of the muscular activation and of the variability of intersegmental coordination. On negative slopes, the stride width is larger, the variability of the stride period and of the inter-segmental coordination is greater and the basic activation patterns become broader, especially at slow speeds. Our findings suggest that the control strategy of downhill walking corresponds to a more conservative gait pattern, which could be adopted to lower the risk of falling at the cost of a greater energy consumption. In uphill walking, where metabolic demands are high, the strategy adopted may be planned to minimise energy expenditure.

The physiology of rowing with perspective on training and health

Abstract: This review presents a perspective on the expansive literature on rowing. The PubMed database was searched for the most relevant literature, while some information was obtained from books. Following the life span of former rowers paved the way to advocate exercise for health promotion. Rowing involves almost all muscles during the stroke and competition requires a large oxygen uptake, which is challenged by the pulmonary diffusion capacity and restriction in blood flow to the muscles. Unique training adaptations allow for simultaneous engagement of the legs in the relatively slow movement of the rowing stroke that, therefore, involves primarily slow-twitch muscle fibres. Like other sport activities, rowing is associated with adaptation not only of the heart, including both increased internal diameters and myocardial size, but also skeletal muscles with hypertrophy of especially slow-twitch muscle fibres. The high metabolic requirement of intense rowing reduces blood pH and, thereby, arterial oxygen saturation decreases as arterial oxygen tension becomes affected. Competitive rowing challenges most systems in the body including pulmonary function and circulatory control with implication for cerebral blood flow and neuromuscular activation. Thus, the physiology of rowing is complex, but it obviously favours large individuals with arms and legs that allow the development of a long stroke. Present inquiries include the development of an appropriately large cardiac output despite the Valsalva-like manoeuvre associated with the stroke, and the remarkable ability of the brain to maintain motor control and metabolism despite marked reductions in cerebral blood flow and oxygenation.

Impact of acute mental stress on segmental arterial stiffness

Abstract: It has been reported that acute brief episodes of mental stress (MS) result in a prolonged increase in carotid-femoral pulse wave velocity (cfPWV), an index of aortic stiffness. However, whether acute MS also impacts arterial stiffness in other segments is unclear. The present study aimed to examine the impact of acute MS on segmental arterial stiffness. In the main experiment, 17 young male subjects (mean age, 20.1 ± 0.7 years) performed a 5-min MS and control (CON) task in a random order. Pulse wave velocity (PWV) from the heart to the brachium (hbPWV) and the ankle (haPWV), PWV between the brachial artery and the ankle (baPWV), and the cardio-ankle vascular index (CAVI) were simultaneously measured at baseline and 5, 15, and 30 min after the task. Compared to baseline values, hbPWV, baPWV, haPWV, and CAVI significantly increased until 30 min after the MS task, whereas these variables did not significantly change following the CON task. At 5 and 30 min after the MS task, percentage changes from baseline were significantly higher in hbPWV (+ 5.2 ± 4.4 and 6.6 ± 4.9%) than in baPWV (+ 2.2 ± 2.1 and 2.2 ± 2.0%) or haPWV (+ 3.6 ± 2.6 and 4.3 ± 2.9%) and were also significantly lower in baPWV than in haPWV. These findings suggest that acute MS elicits an increase in arterial stiffness in various segments and this arterial stiffening is not uniform among the segments.

Ultrasound speckle tracking of Achilles tendon in individuals with unilateral tendinopathy: a pilot study

Abstract: Differential displacement between tendon layers has been shown to occur within the healthy Achilles tendon, and changes of this mechanism have been proposed to result in shear forces, which potentially could lead to tendinopathy. The magnitude of displacement between the tendon layers in tendinopathy is unknown. The purpose of this study was to investigate Achilles tendon layer displacement in individuals suffering from unilateral tendinopathy compared with the asymptomatic contralateral side. Ten participants (9 men and 1 woman 45 ± 10 years, BMI: 28 ± 5) with unilateral Achilles tendinopathy were included. Intra-tendinous motion was assessed using ultrasonography during dynamic unilateral heel rises in standing and seated position. Speckle displacement was determined using a cross-correlation algorithm, in four independent rows, representing superficial and deep tendon layers. The most superficial layer displaced less than the deepest in all condition, except standing for the tendinopathic leg. There was a strong tendency (p = 0.054) for the displacement difference being reduced in the tendinopathic tendon (Tendinopathic side: 0.52 ± 0.16 mm vs. asymptomatic contralateral side: 1.02 ± 0.18 mm). These novel data suggest that the presence of tendinopathy diminishes intra-tendinous sliding in the Achilles tendon.

Short-term isothermic heat acclimation elicits beneficial adaptations but medium-term elicits a more complete adaptation

Abstract: To investigate the effects of 60 min daily, short-term (STHA) and medium-term (MTHA) isothermic heat acclimation (HA) on the physiological and perceptual responses to exercise heat stress. Sixteen, ultra-endurance runners (female = 3) visited the laboratory on 13 occasions. A 45 min sub-maximal (40% Wmax) cycling heat stress test (HST) was completed in the heat (40 °C, 50% relative humidity) on the first (HSTPRE), seventh (HSTSTHA) and thirteenth (HSTMTHA) visit. Participants completed 5 consecutive days of a 60 min isothermic HA protocol (target Tre 38.5 °C) between HSTPRE and HSTSTHA and 5 more between HSTSTHA and HSTMTHA. Heart rate (HR), rectal (Tre), skin (Tsk) and mean body temperature (Tbody), perceived exertion (RPE), thermal comfort (TC) and sensation (TS) were recorded every 5 min. During HSTs, cortisol was measured pre and post and expired air was collected at 15, 30 and 45 min. At rest, Tre and Tbody were lower in HSTSTHA and HSTMTHA compared to HSTPRE, but resting HR was not different between trials. Mean exercising Tre, Tsk, Tbody, and HR were lower in both HSTSTHA and HSTMTHA compared to HSTPRE. There were no differences between HSTSTHA and HSTMTHA. Perceptual measurements were lowered by HA and further reduced during HSTMTHA. A 60 min a day isothermic STHA was successful at reducing physiological and perceptual strain experienced when exercising in the heat; however, MTHA offered a more complete adaptation.

Comfortable walking speed and energy cost of locomotion in patients with multiple sclerosis

Abstract: Comfortable walking speed and energy cost of walking are physiological markers of metabolic activity during gait. People with multiple sclerosis are characterized by altered gait biomechanics and energetics, related to the degree of disability and spasticity, which lead to an increased energy cost of walking. Several studies concerning the energy cost of walking in multiple sclerosis have been published. Nevertheless, differences in protocols and characteristics of the sample have led to different outcomes. The aim of the present meta-analysis is to summarize results from studies with specific inclusion characteristics, and to present data about the comfortable walking speed and the energy cost of walking at that speed. Moreover, a detailed discussion of the potential mechanisms involved in the altered metabolic activity during exercise was included. A total of 19 studies were considered, 12 of which were also part of the quantitative analysis. Despite the strict selection process, high between-group heterogeneity was found for both outcomes. Nevertheless, the overall results suggest a pooled mean comfortable walking speed of 1.12 m/s (95% CI 1.05–1.18) and energy cost of 0.19 mLO2/kg/m (95% CI 0.17–0.21). These findings support the results of previous studies suggesting that energy cost of walking may be increased by 2–3 times compared to healthy controls (HC), and encourage the use of this marker in association with other parameters of the disease.

Increased level of circulating cell-free mitochondrial DNA due to a single bout of strenuous physical exercise

Abstract: Physical exercise is reported to affect the immune response in various ways. Thus, the levels of pro-inflammatory cytokines as well as the abundance of circulating leukocytes are changed. In this study, the occurence of circulating cell-free mitochondrial DNA (cfmtDNA) and nuclear DNA (nDNA) was investigated in connection with a single bout of strenuous physical exercise. Healthy volunteers performed a controlled ergo-spirometry cycle test and venous blood samples were taken at different time-points to analyze the concentration of blood components before, during and after the test. The number of circulating leukocytes was measured, as well as secretion of the soluble urokinase activator receptor (suPAR). Cf-mtDNA significantly increased during exercise, compared to baseline values and after 30 and 90 min of rest. Circulating leukocytes increased during exercise, but returned to baseline levels afterwards. Surface expression of the urokinase plasminogen activating receptor (uPAR) on neutrophils decreased significantly during exercise. The concentration of suPAR tended to increase during exercise but only significantly after 90 min of rest. Increased concentration of cf-mtDNA indicates that cell damage takes place during high intensity training. Hypoxia and tissue damage are likely causes of cf-mtDNA from muscle cells. The levels of cf-mtDNA remain high during the initial rest, due to the decreasing numbers of leukocytes normally clearing the plasma from cf-mtDNA. The increased levels of suPAR further emphasize that strenuous physical exercise causes a reaction similar to inflammation. Further studies are needed to detect the source of increased cf-mtDNA and the corresponding increase of suPAR liberation.

Lunge exercises with blood-flow restriction induces post-activation potentiation and improves vertical jump performance

Abstract: This study examined the post-activation potentiation effects of body-weight lunge exercises with blood-flow restriction on jump performance. Eighteen anaerobically trained men took part in this study across 3 weeks. During the first week, participants were familiarised with the lunge exercises with blood-flow restriction and the drop-jump protocol. In the second and third week, participants were randomly allocated to complete body-weight lunges (three sets of eight repetitions) either with or without blood-flow restriction (occlusion set at 130% of systolic blood pressure) to induce post-activation potentiation. Drop-jump performance was assessed between blood-flow conditions, and prior to, and at the third, sixth, ninth, twelfth and fifteenth minute following each lunge exercise. Relationships between mechanical contributors of jump performance and final jump performance were examined via Pearson correlation coefficients. Lunges with blood-flow restriction significantly improved jump height (~ 4.5% ± 0.8%), flight time (~ 3.4% ± 0.3%) and power (~ 4.1% ± 0.3%) within 6–15 min post-exercise (p 0.05) were found in jump performance measures following lunge exercises without blood-flow restriction. Significant correlations (p < 0.05) between mechanical contributors of jump performance and jump performance highlighted the potential of blood-flow restriction to enhance stretch–shortening cycle mechanics in the current study. Lunge exercises with blood-flow restriction improved subsequent jump performance in anaerobically trained men. The use of blood-flow restriction may be a practical alternative to heavy resistance training equipment during warm-up protocols.

Caloric restriction induces anabolic resistance to resistance exercise

Abstract: Weight loss can result in the loss of muscle mass and bone mineral density. Resistance exercise is commonly prescribed to attenuate these effects. However, the anabolic endocrine response to resistance exercise during caloric restriction has not been characterized. Participants underwent 3-day conditions of caloric restriction (15 kcal kg FFM−1) with post-exercise carbohydrate (CRC) and with post-exercise protein (CRP), and an energy balance control (40 kcal kg FFM−1) with post-exercise carbohydrate (CON). Serial blood draws were taken following five sets of five repetitions of the barbell back squat exercise on day 3 of each condition. In CRC and CRP, respectively, growth hormone peaked at 2.6 ± 0.4 and 2.5 ± 0.9 times the peak concentrations observed during CON. Despite this, insulin-like growth factor-1 concentrations declined 18.3 ± 3.4% in CRC and 27.2 ± 3.8% in CRP, which was greater than the 7.6 ± 3.6% decline in CON, over the subsequent 24 h. Sclerostin increased over the first 2 days of each intervention by 19.2 ± 5.6% in CRC, 21.8 ± 6.2% in CRP and 13.4 ± 5.9% in CON, but following the resistance exercise bout, these increases were attenuated and no longer significant. During caloric restriction, there is considerable endocrine anabolic resistance to a single bout of resistance exercise which persists in the presence of post-exercise whey protein supplementation. Alternative strategies to restore the sensitivity of insulin-like growth factor-1 to growth hormone need to be explored.