Intensified training augments cardiac function, but not blood volume, in male youth elite ice hockey team players.

While it is well-established that a period of interval training performed at near maximal effort, such as speed endurance training (SET), enhances intense exercise performance in well-trained individuals, less is known about its effect on cardiac morphology and function as well as blood volume. To investigate this, we subjected 12 Under-20 Danish national team ice hockey players (age 18 ± 1 years, mean ± SD) to 4 weeks of SET, consisting of 6-10 × 20 s skating bouts at maximal effort interspersed by 2 min of recovery conducted three times weekly. This was followed by 4 weeks of regular training (follow-up). We assessed resting cardiac function and dimensions using transthoracic echocardiography and quantified total blood volume with the carbon monoxide rebreathing technique at three time points: before SET, after SET and after the follow-up period. After SET, stroke volume had increased by 10 (2-18) mL (mean (95% CI)), left atrial end-diastolic volume by 10 (3-17) mL, and circumferential strain improved by 0.9%-points (1.7-0.1) (all P < 0.05). At follow-up, circumferential strain and left atrial end-diastolic volume were reverted to baseline levels, while stroke volume remained elevated. Blood volume and morphological parameters for the left ventricle, including mass and end-diastolic volume, did not change during the study. In conclusion, our findings demonstrate that a brief period of SET elicits beneficial central cardiac adaptations in elite ice hockey players independent of changes in blood volume.

Beyond bronchodilation: Illuminating the performance benefits of inhaled beta2 -agonists in sports.

Given the prevalent use of inhaled beta2 -agonists in sports, there is an ongoing debate as to whether they enhance athletic performance. Over the last decades, inhaled beta2 -agonists have been claimed not to enhance performance with little consideration of dose or exercise modality. In contrast, orally administered beta2 -agonists are perceived as being performance enhancing, predominantly on muscle strength and sprint ability, but can also induce muscle hypertrophy and slow-to-fast fiber phenotypic switching. But because inhaled beta2 -agonists are more efficient to achieve high systemic concentrations than oral delivery relative to dose, it follows that the inhaled route has the potential to enhance performance too. The question is at which inhaled doses such effects occur. While supratherapeutic doses of inhaled beta2 -agonists enhance muscle strength and short intense exercise performance, effects at low therapeutic doses are less apparent. However, even high therapeutic inhaled doses of commonly used beta2 -agonists have been shown to induce muscle hypertrophy and to enhance sprint performance. This is concerning from an anti-doping perspective. In this paper, we raise awareness of the circumstances under which inhaled beta2 -agonists can constitute a performance-enhancing benefit.

Inhaled beta2 -agonist, formoterol, enhances intense exercise performance, and sprint ability in elite cyclists.

PURPOSE: Many athletes use long-acting beta2 -agonist formoterol in treatment of asthma. However, studies in non-athlete cohorts demonstrate that inhaled formoterol can enhance sprint performance calling into question whether its use in competitive sports should be restricted. We investigated whether formoterol at upper recommended inhaled doses (54 µg) would enhance sprint ability and intense exercise performance in elite cyclists. METHODS: Twenty-one male cyclists (V̇O2max : 70.4 ± 4.3 mL × min-1 × kg-1 , mean ± SD) completed two 6-s all-out sprints followed by 4-min all-out cycling after inhaling either 54 µg formoterol or placebo. We also assessed cyclists' leg muscle mass by dual-energy X-ray absorptiometry and muscle fiber type distribution of vastus lateralis biopsies. RESULTS: Peak and mean power output during the 6-s sprint was 32 W (95% CI, 19-44 W, p < 0.001) and 36 W (95% CI, 24-48 W, p < 0.001) higher with formoterol than placebo, corresponding to an enhancing effect of around 3%. Power output during 4-min all-out cycling was 9 W (95% CI, 2-16 W, p = 0.01) greater with formoterol than placebo, corresponding to an enhancing effect of 2.3%. Performance changes in response to formoterol were unrelated to cyclists' VO2max and leg lean mass, whereas muscle fiber Type I distribution correlated with change in sprinting peak power in response to formoterol (r2 = 0.314, p = 0.012). CONCLUSION: Our findings demonstrate that an inhaled one-off dose of 54 µg formoterol has a performance-enhancing potential on sprint ability and short intense performance in elite male cyclists, which is irrespective of training status but partly related to muscle fiber type distribution for sprint ability.

Asthma and exercise-induced bronchoconstriction in athletes: Diagnosis, treatment, and anti-doping challenges.

Athletes often experience lower airway dysfunction, such as asthma and exercise-induced bronchoconstriction (EIB), which affects more than half the athletes in some sports, not least in endurance sports. Symptoms include coughing, wheezing, and breathlessness, alongside airway narrowing, hyperresponsiveness, and inflammation. Early diagnosis and management are essential. Not only because untreated or poorly managed asthma and EIB potentially affects competition performance and training, but also because untreated airway inflammation can result in airway epithelial damage, remodeling, and fibrosis. Asthma and EIB do not hinder performance, as advancements in treatment strategies have made it possible for affected athletes to compete at the highest level. However, practitioners and athletes must ensure that the treatment complies with general guidelines and anti-doping regulations to prevent the risk of a doping sanction because of inadvertently exceeding specified dosing limits. In this review, we describe considerations and challenges in diagnosing and managing athletes with asthma and EIB. We also discuss challenges facing athletes with asthma and EIB, while also being subject to anti-doping regulations.

No additive effect of creatine, caffeine, and sodium bicarbonate on intense exercise performance in endurance-trained individuals.

BACKGROUND: Athletes commonly use creatine, caffeine, and sodium bicarbonate for performance enhancement. While their isolated effects are well-described, less is known about their potential additive effects. METHODS: Following a baseline trial, we randomized 12 endurance-trained males (age: 25 ± 5 years, VO2max: 56.7 ± 4.6 mL kg-1 min-1; mean ± SD) and 11 females (age: 25 ± 3 years, VO2max: 50.2 ± 3.4 mL kg-1 min-1) to 5 days of creatine monohydrate (0.3 g kg-1 per day) or placebo loading, followed by a daily maintenance dose (0.04 g kg-1) throughout the study. After the loading period, subjects completed four trials in randomized order where they ingested caffeine (3 mg kg-1), sodium bicarbonate (0.3 g kg-1), placebo, or both caffeine and sodium bicarbonate before a maximal voluntary contraction (MVC), 15-s sprint, and 6-min time trial. RESULTS: Compared to placebo, mean power output during 15-s sprint was higher following loading with creatine than placebo (+34 W, 95% CI: 10 to 58, p = 0.008), but with no additional effect of caffeine (+10 W, 95% CI: -7 to 24, p = 0.156) or sodium bicarbonate (+5 W, 95% CI: -4 to 13, p = 0.397). Mean power output during 6-min time trial was higher with caffeine (+12 W, 95% CI: 5 to 18, p = 0.001) and caffeine + sodium bicarbonate (+8 W, 95% CI: 0 to 15, p = 0.038), whereas sodium bicarbonate (-1 W, 95% CI: -7 to 6, p = 0.851) and creatine (-6 W, 95% CI: -15 to 4, p = 0.250) had no effects. CONCLUSION: While creatine and caffeine can enhance sprint- and time trial performance, respectively, these effects do not seem additive. Therefore, supplementing with either creatine or caffeine appears sufficient to enhance sprint or short intense exercise performance.

Importance of training volume during intensified training in elite cyclists: Maintained vs. reduced volume at moderate intensity.

INTRODUCTION: Male elite cyclists (average VO2 -max: 71 mL/min/kg, n = 18) completed 7 weeks of high-intensity interval training (HIT) (3×/week; 4-min and 30-s intervals) during the competitive part of the season. The influence of a maintained or lowered total training volume combined with HIT was evaluated in a two-group design. Weekly moderate-intensity training was lowered by ~33% (~5 h) (LOW, n = 8) or maintained at normal volume (NOR, n = 10). Endurance performance and fatigue resistance were evaluated via 400 kcal time-trials (~20 min) commenced either with or without prior completion of a 120-min preload (including repeated 20-s sprints to simulate physiologic demands during road races). RESULTS: Time-trial performance without preload was improved after the intervention (p = 0.006) with a 3% increase in LOW (p = 0.04) and a 2% increase in NOR (p = 0.07). Preloaded time-trial was not significantly improved (p = 0.19). In the preload, average power during repeated sprinting increased by 6% in LOW (p < 0.01) and fatigue resistance in sprinting (start vs end of preload) was improved (p < 0.05) in both groups. Blood lactate during the preload was lowered (p < 0.001) solely in NOR. Measures of oxidative enzyme activity remained unchanged, whereas the glycolytic enzyme PFK increased by 22% for LOW (p = 0.02). CONCLUSION: The present study demonstrates that elite cyclists can benefit from intensified training during the competitive season both with maintained and lowered training volume at moderate intensity. In addition to benchmarking the effects of such training in ecological elite settings, the results also indicate how some performance and physiological parameters may interact with training volume.

Beta2-Adrenergic Stimulation Induces Resistance Training-Like Adaptations in Human Skeletal Muscle: Potential Role of KLHL41.

Skeletal muscle mass plays a pivotal role in metabolic function, but conditions such as bed rest or injury often render resistance training impractical. The beta2-adrenergic receptor has been highlighted as a potential target to promote muscle hypertrophy and treat atrophic conditions. Here, we investigate the proteomic changes associated with beta2-adrenergic-mediated muscle hypertrophy, using resistance training as a hypertrophic comparator. We utilize MS-based proteomics to map skeletal muscle proteome remodeling in response to beta2-adrenergic stimulation or resistance training as well as cell model validation. We report that beta2-adrenergic stimulation mimics multiple features of resistance training in proteome-wide remodeling, comprising systematic upregulation of ribosomal subunits and concomitant downregulation of mitochondrial proteins. Approximately 20% of proteins were regulated in both conditions, comprising proteins involved in steroid metabolism (AKR1C1, AKR1C2, AKRC1C3), protein-folding (SERPINB1), and extracellular matrix organization (COL1A1, COL1A2). Among overall most significantly upregulated proteins were kelch-like family members (KLHL) 40 and 41. In follow-up experiments, we identify KLHL41 as having novel implications for beta2-adrenergic-mediated muscle hypertrophy. Treating C2C12 cells with beta2-agonist for 96 h increased myotube diameter by 48% (p < 0.001). This anabolic effect was abolished by prior knockdown of KLHL41. Using siRNA, KLHL41 abundance was decreased by 60%, and the anabolic response to beta2-agonist was diminished (+ 15%, i.e., greater in the presence of KLHL41, knock-down × treatment: p = 0.004). In conclusion, protein-wide remodeling induced by beta2-adrenergic stimulation mimics multiple features of resistance training, and thus the beta2-adrenergic receptor may be a target with therapeutic potential in the treatment of muscle wasting conditions without imposing mechanical load.

Airway hyperresponsiveness reflects corticosteroid-sensitive mast cell involvement across asthma phenotypes.

BACKGROUND: Airway hyperresponsiveness is a hallmark of asthma across asthma phenotypes. Airway hyperresponsiveness to mannitol specifically relates to mast cell infiltration of the airways, suggesting inhaled corticosteroids to be effective in reducing the response to mannitol, despite low levels of type 2 inflammation. OBJECTIVE: We sought to investigate the relationship between airway hyperresponsiveness and infiltrating mast cells, and the response to inhaled corticosteroid treatment. METHODS: In 50 corticosteroid-free patients with airway hyperresponsiveness to mannitol, mucosal cryobiopsies were obtained before and after 6 weeks of daily treatment with 1600 µg of budesonide. Patients were stratified according to baseline fractional exhaled nitric oxide (Feno) with a cutoff of 25 parts per billion. RESULTS: Airway hyperresponsiveness was comparable at baseline and improved equally with treatment in both patients with Feno-high and Feno-low asthma: doubling dose, 3.98 (95% CI, 2.49-6.38; P < .001) and 3.85 (95% CI, 2.51-5.91; P < .001), respectively. However, phenotypes and distribution of mast cells differed between the 2 groups. In patients with Feno-high asthma, airway hyperresponsiveness correlated with the density of chymase-high mast cells infiltrating the epithelial layer (ρ, -0.42; P = .04), and in those with Feno-low asthma, it correlated with the density in the airway smooth muscle (ρ, -0.51; P = .02). The improvement in airway hyperresponsiveness after inhaled corticosteroid treatment correlated with a reduction in mast cells, as well as in airway thymic stromal lymphopoietin and IL-33. CONCLUSIONS: Airway hyperresponsiveness to mannitol is related to mast cell infiltration across asthma phenotypes, correlating with epithelial mast cells in patients with Feno-high asthma and with airway smooth muscle mast cells in patients with Feno-low asthma. Treatment with inhaled corticosteroids was effective in reducing airway hyperresponsiveness in both groups.

Effect of sample fractionation and normalization when immunoblotting for human muscle Na+/K+-ATPase subunits and glycogen synthase.

Immunoblotting is widely used in muscle physiology to determine protein regulation and abundance. However, research groups use different protocols, which may result in differential outcomes. Herein, we investigated the effect of various homogenization procedures on determination of protein abundance in human m. vastus lateralis biopsies. Furthermore, we investigated differences in abundance between young healthy males (n = 12) and type-2 diabetics (n = 4), and the effect of data normalization. Fractionated lysates had the lowest variation in total protein determination as compared to non-fractionated homogenates. Abundance of NKAα2, NKAß1, FXYD1, and glycogen synthase was higher (P < 0.05) in young healthy than in type-2 diabetics determined in both fractionated and non-fractionated samples for which normalization to the stain-free signal and/or standard curve did not affect outcomes. Precision and reliability of protein abundance determination between sample types showed a moderate to good reliability for these proteins, whereas the commonly used house-keeping protein, actin, showed poor reliability. In conclusion, fractionated and non-fractionated immunoblotting samples yield similar data for several sarcolemmal and cytosolic proteins, except for actin, which, therefore appears inappropriate for data normalization in immunoblotting of human skeletal muscle. Thus, fractionation does not seem to be a major source of bias when immunoblotting for NKA subunits and GS.

High-Intensity Training Represses FXYD5 and Glycosylates Na,K-ATPase in Type II Muscle Fibres, Which Are Linked with Improved Muscle K+ Handling and Performance.

Na+/K+ ATPase (NKA) comprises several subunits to provide isozyme heterogeneity in a tissue-specific manner. An abundance of NKA α, ß, and FXYD1 subunits is well-described in human skeletal muscle, but not much is known about FXYD5 (dysadherin), a regulator of NKA and ß1 subunit glycosylation, especially with regard to fibre-type specificity and influence of sex and exercise training. Here, we investigated muscle fibre-type specific adaptations in FXYD5 and glycosylated NKAß1 to high-intensity interval training (HIIT), as well as sex differences in FXYD5 abundance. In nine young males (23.8 ± 2.5 years of age) (mean ± SD), 3 weekly sessions of HIIT for 6 weeks enhanced muscle endurance (220 ± 102 vs. 119 ± 99 s, p < 0.01) and lowered leg K+ release during intense knee-extensor exercise (0.5 ± 0.8 vs. 1.0 ± 0.8 mmol·min-1, p < 0.01) while also increasing cumulated leg K+ reuptake 0-3 min into recovery (2.1 ± 1.5 vs. 0.3 ± 0.9 mmol, p < 0.01). In type IIa muscle fibres, HIIT lowered FXYD5 abundance (p < 0.01) and increased the relative distribution of glycosylated NKAß1 (p < 0.05). FXYD5 abundance in type IIa muscle fibres correlated inversely with the maximal oxygen consumption (r = -0.53, p < 0.05). NKAα2 and ß1 subunit abundances did not change with HIIT. In muscle fibres from 30 trained males and females, we observed no sex (p = 0.87) or fibre type differences (p = 0.44) in FXYD5 abundance. Thus, HIIT downregulates FXYD5 and increases the distribution of glycosylated NKAß1 in type IIa muscle fibres, which is likely independent of a change in the number of NKA complexes. These adaptations may contribute to counter exercise-related K+ shifts and enhance muscle performance during intense exercise.

The beta2 -adrenergic receptor - a re-emerging target to combat obesity and induce leanness?

Treatment of obesity with repurposed or novel drugs is an expanding research field. One approach is to target beta2 -adrenergic receptors because they regulate the metabolism and phenotype of adipose and skeletal muscle tissue. Several observations support a role for the beta2 -adrenergic receptor in obesity. Specific human beta2 -adrenergic receptor polymorphisms are associated with body composition and obesity, for which the Gln27Glu polymorphism is associated with obesity, while the Arg16Gly polymorphism is associated with lean mass in men and the development of obesity in specific populations. Individuals with obesity also have lower abundance of beta2 -adrenergic receptors in adipose tissue and are less sensitive to catecholamines. In addition, studies in livestock and rodents demonstrate that selective beta2 -agonists induce a so-called 'repartitioning effect' characterized by muscle accretion and reduced fat deposition. In humans, beta2 -agonists dose-dependently increase resting metabolic rate by 10-50%. And like that observed in other mammals, only a few weeks of treatment with beta2 -agonists increases muscle mass and reduces fat mass in young healthy individuals. Beta2 -agonists also exert beneficial effects on body composition when used concomitantly with training and act additively to increase muscle strength and mass during periods with resistance training. Thus, the beta2 -adrenergic receptor seems like an attractive target in the development of anti-obesity drugs. However, future studies need to verify the long-term efficacy and safety of beta2 -agonists in individuals with obesity, particularly in those with comorbidities.

Muscle hypertrophic effect of inhaled beta2 -agonist is associated with augmented insulin-stimulated whole-body glucose disposal in young men.

Rodent studies highlight enhancement of glucose tolerance and insulin sensitivity as potential clinically relevant effects of chronic beta2 -agonist treatment. However, the doses administered to rodents are not comparable with the therapeutic doses used for humans. Thus, we investigated the physiological effects of prolonged beta2 -agonist treatment at inhaled doses resembling those used in respiratory diseases on insulin-stimulated whole-body glucose disposal and putative mechanisms in skeletal muscle and adipose tissue of healthy men. Utilizing a randomized placebo-controlled parallel-group design, we assigned 21 healthy men to 4 weeks daily inhalation of terbutaline (TER; 4 mg × day-1 , n = 13) or placebo (PLA, n = 8). Before and after treatments, we assessed subjects' whole-body insulin-stimulated glucose disposal and body composition, and collected vastus lateralis muscle and abdominal adipose tissue biopsies. Glucose infusion rate increased by 27% (95% CI: 80 to 238 mg × min-1 , P = 0.001) in TER, whereas no significant changes occurred in PLA (95% CI: -37 to 195 mg × min-1 , P = 0.154). GLUT4 content in muscle or adipose tissue did not change, nor did hexokinase II content or markers of mitochondrial volume in muscle. Change in lean mass was associated with change in glucose infusion rate in TER (r = 0.59, P = 0.03). Beta2 -agonist treatment in close-to-therapeutic doses may augment whole-body insulin-stimulated glucose disposal in healthy young men and part of the change is likely to be explained by muscle hypertrophy. These findings highlight the therapeutic potential of beta2 -agonists for improving insulin sensitivity. KEY POINTS: While studies in rodents have highlighted beta2 -agonists as a means to augment insulin sensitivity, these studies utilized beta2 -agonists at doses inapplicable to humans. Herein we show that a 4-week treatment period with daily therapeutic inhalation of beta2 -agonist increases insulin-stimulated whole-body glucose disposal in young healthy lean men. This effect was associated with an increase of lean mass but not with changes in GLUT4 and hexokinase II or basal glycogen content in skeletal muscle nor GLUT4 content in abdominal adipose tissue. These findings suggest that the enhanced insulin-stimulated whole-body glucose disposal induced by a period of beta2 -agonist treatment in humans, at least in part, is attributed to muscle hypertrophy. Our observations extend findings in rodents and highlight the therapeutic potential of beta2 -agonists to enhance the capacity for glucose disposal and whole-body insulin sensitivity, providing important knowledge with potential application in insulin resistance.

Beta2 -agonist increases skeletal muscle interleukin 6 production and release in response to resistance exercise in men.

OBJECTIVE: Several tissues produce and release interleukin-6 (IL-6) in response to beta2 -adrenergic stimulation with selective agonists (beta2 -agonists). Moreover, exercise stimulates muscle IL-6 production, but whether beta2 -agonists regulate skeletal muscle production and release of IL-6 in humans in association with exercise remains to be clarified. Thus, we investigated leg IL-6 release in response to beta2 -agonist salbutamol in lean young men at rest and in recovery from resistance exercise. DESIGN: The study employed a randomized controlled crossover design, where 12 men ingested either salbutamol (16 mg) or placebo for 4 days, followed by the last dose (24 mg) administered 1½ h before exercise. Arterial and femoral venous plasma IL-6 as well as femoral artery blood flow was measured before and ½-5 h in recovery from quadriceps muscle resistance exercise. Furthermore, vastus lateralis muscle biopsies were collected ½ and 5 h after exercise for determination of mRNA levels of IL-6 and Tumor Necrosis Factor (TNF)-α. RESULTS: Average leg IL-6 release was 1.7-fold higher (p = 0.01) for salbutamol than placebo, being 138 ± 76 and 79 ± 66 pg min-1 (mean ± SD) for salbutamol and placebo, respectively, but IL-6 release was not significantly different between treatments within specific sampling points at rest and after exercise. Muscle IL-6 mRNA was 1.5- and 1.7-fold higher (p = 0.001) for salbutamol than placebo ½ and 5 h after exercise, respectively, whereas no significant treatment differences were observed for TNF-α mRNA. CONCLUSIONS: Beta2 -adrenergic stimulation with high doses of the selective beta2 -agonist salbutamol, preceeded by 4 consecutive daily doses, induces transcription of IL-6 in skeletal muscle in response to resistance exercise, and increases muscle IL-6 release in lean individuals.

Discovery of thymosin ß4 as a human exerkine and growth factor.

Skeletal muscle is an endocrine organ secreting exercise-induced factors (exerkines), which play a pivotal role in interorgan cross talk. Using mass spectrometry (MS)-based proteomics, we characterized the secretome and identified thymosin ß4 (TMSB4X) as the most upregulated secreted protein in the media of contracting C2C12 myotubes. TMSB4X was also acutely increased in the plasma of exercising humans irrespective of the insulin resistance condition or exercise mode. Treatment of mice with TMSB4X did not ameliorate the metabolic disruptions associated with diet induced-obesity, nor did it enhance muscle regeneration in vivo. However, TMSB4X increased osteoblast proliferation and neurite outgrowth, consistent with its WADA classification as a prohibited growth factor. Therefore, we report TMSB4X as a human exerkine with a potential role in cellular cross talk.

Nitrate-rich beetroot juice ingestion reduces skeletal muscle O2 uptake and blood flow during exercise in sedentary men.

Dietary nitrate supplementation has been shown to reduce pulmonary O2 uptake during submaximal exercise and enhance exercise performance. However, the effects of nitrate supplementation on local metabolic and haemodynamic regulation in contracting human skeletal muscle remain unclear. To address this, eight healthy young male sedentary subjects were assigned in a randomized, double-blind, crossover design to receive nitrate-rich beetroot juice (NO3, 9 mmol) and placebo (PLA) 2.5 h prior to the completion of a double-step knee-extensor exercise protocol that included a transition from unloaded to moderate-intensity exercise (MOD) followed immediately by a transition to intense exercise (HIGH). Compared with PLA, NO3 increased plasma levels of nitrate and nitrite. During MOD, leg V̇O2 and leg blood flow (LBF) were reduced to a similar extent (∼9%-15%) in NO3. During HIGH, leg V̇O2 was reduced by ∼6%-10% and LBF by ∼5%-9% (did not reach significance) in NO3. Leg V̇O2 kinetics was markedly faster in the transition from passive to MOD compared with the transition from MOD to HIGH both in NO3 and PLA with no difference between PLA and NO3. In NO3, a reduction in nitrate and nitrite concentration was detected between arterial and venous samples. No difference in the time to exhaustion was observed between conditions. In conclusion, elevation of plasma nitrate and nitrate reduces leg skeletal muscle V̇O2 and blood flow during exercise. However, nitrate supplementation does not enhance muscle V̇O2 kinetics during exercise, nor does it improve time to exhaustion when exercising with a small muscle mass. KEY POINTS: Dietary nitrate supplementation has been shown to reduce systemic O2 uptake during exercise and improve exercise performance. The effects of nitrate supplementation on local metabolism and blood flow regulation in contracting human skeletal muscle remain unclear. By using leg exercise engaging a small muscle mass, we show that O2 uptake and blood flow are similarly reduced in contracting skeletal muscle of humans during exercise. Despite slower V̇O2 kinetics in the transition from moderate to intense exercise, no effects of nitrate supplementation were observed for V̇O2 kinetics and time to exhaustion. Nitrate and nitrite concentrations are reduced across the exercising leg, suggesting that these ions are extracted from the arterial blood by contracting skeletal muscle.

Training with blood flow restriction increases femoral artery diameter and thigh oxygen delivery during knee-extensor exercise in recreationally trained men.

KEY POINTS: Endurance-type training with blood flow restriction (BFR) increases maximum oxygen uptake ( V̇O2max ) and exercise endurance of humans. However, the physiological mechanisms behind this phenomenon remain uncertain. In the present study, we show that BFR-interval training reduces the peripheral resistance to oxygen transport during dynamic, submaximal exercise in recreationally-trained men, mainly by increasing convective oxygen delivery to contracting muscles. Accordingly, BFR-training increased oxygen uptake by, and concomitantly reduced net lactate release from, the contracting muscles during relative-intensity-matched exercise, at the same time as invoking a similar increase in diffusional oxygen conductance compared to the training control. Only BFR-training increased resting femoral artery diameter, whereas increases in oxygen transport and uptake were dissociated from changes in the skeletal muscle content of mitochondrial electron-transport proteins. Thus, physically trained men benefit from BFR-interval training by increasing leg convective oxygen transport and reducing lactate release, thereby improving the potential for increasing the percentage of V̇O2max that can be sustained throughout exercise. ABSTRACT: In the present study, we investigated the effect of training with blood flow restriction (BFR) on thigh oxygen transport and uptake, and lactate release, during exercise. Ten recreationally-trained men (50 ± 5 mL kg-1  min-1 ) completed 6 weeks of interval cycling with one leg under BFR (BFR-leg; pressure: ∼180 mmHg) and the other leg without BFR (CON-leg). Before and after the training intervention (INT), thigh oxygen delivery, extraction, uptake, diffusion capacity and lactate release were determined during knee-extensor exercise at 25% incremental peak power output (iPPO) (Ex1), followed by exercise to exhaustion at 90% pre-training iPPO (Ex2), by measurement of femoral-artery blood flow and femoral-arterial and -venous blood sampling. A muscle biopsy was obtained from legs before and after INT to determine mitochondrial electron-transport protein content. Femoral-artery diameter was also measured. In the BFR-leg, after INT, oxygen delivery and uptake were higher, and net lactate release was lower, during Ex1 (vs. CON-leg; P < 0.05), with an 11% larger increase in workload (vs. CON-leg; P < 0.05). During Ex2, after INT, oxygen delivery was higher, and oxygen extraction was lower, in the BFR-leg compared to the CON-leg (P < 0.05), resulting in an unaltered oxygen uptake (vs. CON-leg; P > 0.05). In the CON-leg, at both intensities, oxygen delivery, extraction, uptake and lactate release remained unchanged (P > 0.05). Resting femoral artery diameter increased with INT only in the BFR-leg (∼4%; P < 0.05). Oxygen diffusion capacity was similarly raised in legs (P < 0.05). Mitochondrial protein content remained unchanged in legs (P > 0.05). Thus, BFR-interval training enhances oxygen utilization by, and lowers lactate release from, submaximally-exercising muscles of recreationally-trained men mainly by increasing leg convective oxygen transport.

Effect of aerobic exercise training on asthma in adults: a systematic review and meta-analysis.

OBJECTIVE: To evaluate the effect of aerobic exercise training on asthma control, lung function and airway inflammation in adults with asthma. DESIGN: Systematic review and meta-analysis. METHODS: Randomised controlled trials investigating the effect of ≥8 weeks of aerobic exercise training on outcomes for asthma control, lung function and airway inflammation in adults with asthma were eligible for study. MEDLINE, Embase, CINAHL, PEDro and the Cochrane Central Register of Controlled Trials (CENTRAL) were searched up to April 3, 2019. Risk of bias was assessed using the Cochrane Risk of Bias Tool. RESULTS: We included 11 studies with a total of 543 adults with asthma. Participants' mean (range) age was 36.5 (22-54) years; 74.8% of participants were female and the mean (range) body mass index was 27.6 (23.2-38.1) kg·m-2. Interventions had a median (range) duration of 12 (8-12) weeks and included walking, jogging, spinning, treadmill running and other unspecified exercise training programmes. Exercise training improved asthma control with a standard mean difference (SMD) of -0.48 (-0.81--0.16). Lung function slightly increased with an SMD of -0.36 (-0.72-0.00) in favour of exercise training. Exercise training had no apparent effect on markers of airway inflammation (SMD -0.03 (-0.41-0.36)). CONCLUSIONS: In adults with asthma, aerobic exercise training has potential to improve asthma control and lung function, but not airway inflammation.

High-intensity exercise training enhances mitochondrial oxidative phosphorylation efficiency in a temperature-dependent manner in human skeletal muscle: implications for exercise performance.

The purpose of the present study was to investigate whether exercise training-induced adaptations in human skeletal muscle mitochondrial bioenergetics are magnified under thermal conditions resembling sustained intense contractile activity and whether training-induced changes in mitochondrial oxidative phosphorylation (OXPHOS) efficiency influence exercise efficiency. Twenty healthy men performed 6 wk of high-intensity exercise training [i.e., speed endurance training (SET; n = 10)], or maintained their usual lifestyle (n = 10). Before and after the intervention, mitochondrial respiratory function was determined ex vivo in permeabilized muscle fibers under experimentally-induced normothermia (35°C) and hyperthermia (40°C) mimicking in vivo muscle temperature at rest and during intense exercise, respectively. In addition, activity and content of muscle mitochondrial enzymes and proteins were quantified. Exercising muscle efficiency was determined in vivo by measurements of leg hemodynamics and blood parameters during one-legged knee-extensor exercise. SET enhanced maximal OXPHOS capacity and OXPHOS efficiency at 40°C, but not at 35°C, and attenuated hyperthermia-induced decline in OXPHOS efficiency. Furthermore, SET increased expression of markers of mitochondrial content and up-regulated content of MFN2, DRP1, and ANT1. Also, SET improved exercise efficiency and capacity. These findings indicate that muscle mitochondrial bioenergetics adapts to high-intensity exercise training in a temperature-dependent manner and that enhancements in mitochondrial OXPHOS efficiency may contribute to improving exercise performance.-Fiorenza, M., Lemminger, A. K., Marker, M., Eibye, K., Iaia, F. M., Bangsbo, J., Hostrup, M. High-intensity exercise training enhances mitochondrial oxidative phosphorylation efficiency in a temperature-dependent manner in human skeletal muscle: implications for exercise performance.

Efficacy of 10-20-30 training versus moderate-intensity continuous training on HbA1c, body composition and maximum oxygen uptake in male patients with type 2 diabetes: A randomized controlled trial.

AIM: To compare the efficacy of 10-20-30 training versus moderate-intensity continuous training (MICT) on HbA1c, body composition and maximum oxygen uptake (V˙O2 max) in male patients with type 2 diabetes (T2D). MATERIALS AND METHODS: Fifty-one male participants with T2D were randomly assigned (1:1) to a 10-20-30 (N = 26) and a MICT (N = 25) training group. Interventions consisted of supervised cycling three times weekly for 10 weeks, lasting 29 minutes (10-20-30) and 50 minutes (MICT) in a local non-clinical setting. The primary outcome was change in HbA1c from baseline to 10-week follow-up. RESULTS: Of 51 participants enrolled, 44 (mean age 61.0 ± 6.8 [mean ± SD] years, diagnosed 7.5 ± 5.8 years, baseline HbA1c 7.4% ± 1.3%) were included in the analysis. Training compliance was 84% and 86% in 10-20-30 and MICT, respectively. No adverse events occurred during the intervention. HbA1c decreased (P <0.001) by 0.5 (95% CI -0.72 to -0.21) percentage points with training in 10-20-30, with no change in MICT. The change in 10-20-30 was greater (P <0.05) than in MICT. Visceral fat mass decreased (P <0.05) only with 10-20-30 training, whereas total fat mass decreased (P <0.01) and V˙O2 max increased (P <0.01) with training in both groups. CONCLUSIONS: Ten weeks of 10-20-30 training was superior to MICT in lowering HbA1c, and only 10-20-30 training decreased visceral fat mass in patients with T2D. Furthermore, 10-20-30 training was as effective as MICT in reducing total fat mass and increasing V˙O2 max, despite a 42% lower training time commitment.

Cycling with blood flow restriction improves performance and muscle K+ regulation and alters the effect of anti-oxidant infusion in humans.

KEY POINTS: Training with blood flow restriction (BFR) is a well-recognized strategy for promoting muscle hypertrophy and strength. However, its potential to enhance muscle function during sustained, intense exercise remains largely unexplored. In the present study, we report that interval training with BFR augments improvements in performance and reduces net K+ release from contracting muscles during high-intensity exercise in active men. A better K+ regulation after BFR-training is associated with an elevated blood flow to exercising muscles and altered muscle anti-oxidant function, as indicated by a higher reduced to oxidized glutathione (GSH:GSSG) ratio, compared to control, as well as an increased thigh net K+ release during intense exercise with concomitant anti-oxidant infusion. Training with BFR also invoked fibre type-specific adaptations in the abundance of Na+ ,K+ -ATPase isoforms (α1 , ß1 , phospholemman/FXYD1). Thus, BFR-training enhances performance and K+ regulation during intense exercise, which may be a result of adaptations in anti-oxidant function, blood flow and Na+ ,K+ -ATPase-isoform abundance at the fibre-type level. ABSTRACT: We examined whether blood flow restriction (BFR) augments training-induced improvements in K+ regulation and performance during intense exercise in men, and also whether these adaptations are associated with an altered muscle anti-oxidant function, blood flow and/or with fibre type-dependent changes in Na+ ,K+ -ATPase-isoform abundance. Ten recreationally-active men (25 ± 4 years, 49.7 ± 5.3 mL kg-1  min-1 ) performed 6 weeks of interval cycling, where one leg trained without BFR (control; CON-leg) and the other trained with BFR (BFR-leg, pressure: ∼180 mmHg). Before and after training, femoral arterial and venous K+ concentrations and artery blood flow were measured during single-leg knee-extensor exercise at 25% (Ex1) and 90% of thigh incremental peak power (Ex2) with i.v. infusion of N-acetylcysteine (NAC) or placebo (saline) and a resting muscle biopsy was collected. After training, performance increased more in BFR-leg (23%) than in CON-leg (12%, P < 0.05), whereas K+ release during Ex2 was attenuated only from BFR-leg (P < 0.05). The muscle GSH:GSSG ratio at rest and blood flow during exercise was higher in BFR-leg than in CON-leg after training (P < 0.05). After training, NAC increased resting muscle GSH concentration and thigh net K+ release during Ex2 only in BFR-leg (P < 0.05), whereas the abundance of Na+ ,K+ -ATPase-isoform α1 in type II (51%), ß1 in type I (33%), and FXYD1 in type I (108%) and type II (60%) fibres was higher in BFR-leg than in CON-leg (P < 0.05). Thus, training with BFR elicited greater improvements in performance and reduced thigh K+ release during intense exercise, which were associated with adaptations in muscle anti-oxidant function, blood flow and Na+ ,K+ -ATPase-isoform abundance at the fibre-type level.