Metabolic alkalosis reduces exercise-induced acidosis and potassium accumulation in human skeletal muscle interstitium

Oral but Not Topical Sodium Bicarbonate Improves Repeated Sprint Performance During Simulated Soccer Match Play Exercise in Collegiate Athletes

This study investigated the effect of oral and topical sodium bicarbonate (SB) on soccer-specific performance during simulated soccer exercise. In a block randomized, double-blind, crossover design, 10 collegiate male soccer players (stature: 181.7 ± 3.2 cm, body mass: 81.7 ± 10.5 kg) performed soccer-specific performance tests (countermovement jumps, Illinois agility, 8 × 25 m repeated sprints) throughout a 90-min soccer-specific aerobic field test (SAFT90) following 0.3 g/kg body mass SB in capsules (SB-ORAL), 0.9036 g/kg body mass PR Lotion (SB-LOTION), or placebo capsules and lotion (PLA). Soccer-specific performance tests were conducted pre-SAFT90, during half-time and post-SAFT90. Blood samples were analyzed for acid-base balance (pH; bicarbonate, HCO3-) and strong ions (sodium, Na+; potassium, K+). Average sprint times were quicker for SB-ORAL than PLA during half-time (3.7%; p = .049; g = .57) and post-SAFT90 (4.9%; p = .041; g = .66). SB-ORAL increased pH and HCO3- prewarm-up and during half-time (p < .05), and lowered K+ during half-time (p = .035) compared with PLA. SB-LOTION increased pH (p = .019) and lowered K+ (p = .012) during half-time compared with PLA. SB-LOTION increased Na+ postexercise compared with PLA (p = .008). Repeated sprint times during simulated soccer exercise improved for SB-ORAL, which might have been mechanistically underpinned by elevated blood buffering capacity and greater regulation of strong ion concentration. Consuming SB in capsules is a more effective strategy than topical SB application for improving blood buffering capacity and repeated sprint performance throughout competitive soccer matches.

A century of exercise physiology: effects of muscle contraction and exercise on skeletal muscle Na+,K+-ATPase, Na+ and K+ ions, and on plasma K+ concentration-historical developments

This historical review traces key discoveries regarding K+ and Na+ ions in skeletal muscle at rest and with exercise, including contents and concentrations, Na+,K+-ATPase (NKA) and exercise effects on plasma [K+] in humans. Following initial measures in 1896 of muscle contents in various species, including humans, electrical stimulation of animal muscle showed K+ loss and gains in Na+, Cl- and H20, then subsequently bidirectional muscle K+ and Na+ fluxes. After NKA discovery in 1957, methods were developed to quantify muscle NKA activity via rates of ATP hydrolysis, Na+/K+ radioisotope fluxes, [3H]-ouabain binding and phosphatase activity. Since then, it became clear that NKA plays a central role in Na+/K+ homeostasis and that NKA content and activity are regulated by muscle contractions and numerous hormones. During intense exercise in humans, muscle intracellular [K+] falls by 21 mM (range - 13 to - 39 mM), interstitial [K+] increases to 12-13 mM, and plasma [K+] rises to 6-8 mM, whilst post-exercise plasma [K+] falls rapidly, reflecting increased muscle NKA activity. Contractions were shown to increase NKA activity in proportion to activation frequency in animal intact muscle preparations. In human muscle, [3H]-ouabain-binding content fully quantifies NKA content, whilst the method mainly detects α2 isoforms in rats. Acute or chronic exercise affects human muscle K+, NKA content, activity, isoforms and phospholemman (FXYD1). Numerous hormones, pharmacological and dietary interventions, altered acid-base or redox states, exercise training and physical inactivity modulate plasma [K+] during exercise. Finally, historical research approaches largely excluded female participants and typically used very small sample sizes.

Sodium Bicarbonate Ingestion in a Fasted State Improves 16.1-km Cycling Time-Trial Performance

PURPOSE

The use of sodium bicarbonate (SB) as a preexercise ergogenic aid has been extensively studied in short-duration high-intensity exercise. Very few studies have considered the effects of SB ingestion before prolonged high-intensity exercise. The aim of the present study was to determine the effects of a 0.3 g·kg -1 body mass dose of SB ingested before the start of a 16.1-km cycling time trial in cyclists.

METHOD

Ten trained male cyclists (age, 31.1 ± 9 yr; height, 1.84 ± 0.05 m; body mass, 82.8 ± 8.5 kg; and V̇O 2peak , 60.4 ± 3.1 mL·kg -1 ·min -1 ) completed this study. Participants ingested 0.3 g·kg -1 in gelatine (SB-G) and enteric capsules (SB-E) 1 wk apart to determine individualized time-to-peak alkalosis for each ingestion form. Using a randomized crossover design, participants then performed simulated 16.1-km time trials after ingestion of SB-G, SB-E, or a placebo.

RESULTS

There were significant differences in performance between the SB and placebo ingestion strategies ( f = 5.50, P = 0.014, p η2 = 0.38). Performance time was significantly improved by SB ingestion (mean improvement: 34.4 ± 42.6 s ( P = 0.031) and 40.4 ± 45.5 s ( P = 0.020) for SB-G and SB-E, respectively) compared with the placebo. Gastrointestinal symptoms were lower after SB-E compared with SB-G (36.3 ± 4.5 vs 5.6 ± 3.1 AU, P < 0.001, g = 7.09).

CONCLUSIONS

This study demonstrates that increased buffering capacity after acute preexercise SB ingestion can improve endurance cycling time-trial performances. The use of SB could be considered for use in 16.1-km cycling time trials, but further work is required to establish these effects after a preexercise meal.

Exercise and fatigue: integrating the role of K+, Na+ and Cl- in the regulation of sarcolemmal excitability of skeletal muscle

Perturbations in K+ have long been considered a key factor in skeletal muscle fatigue. However, the exercise-induced changes in K+ intra-to-extracellular gradient is by itself insufficiently large to be a major cause for the force decrease during fatigue unless combined to other ion gradient changes such as for Na+. Whilst several studies described K+-induced force depression at high extracellular [K+] ([K+]e), others reported that small increases in [K+]e induced potentiation during submaximal activation frequencies, a finding that has mostly been ignored. There is evidence for decreased Cl- ClC-1 channel activity at muscle activity onset, which may limit K+-induced force depression, and large increases in ClC-1 channel activity during metabolic stress that may enhance K+ induced force depression. The ATP-sensitive K+ channel (KATP channel) is also activated during metabolic stress to lower sarcolemmal excitability. Taking into account all these findings, we propose a revised concept in which K+ has two physiological roles: (1) K+-induced potentiation and (2) K+-induced force depression. During low-moderate intensity muscle contractions, the K+-induced force depression associated with increased [K+]e is prevented by concomitant decreased ClC-1 channel activity, allowing K+-induced potentiation of sub-maximal tetanic contractions to dominate, thereby optimizing muscle performance. When ATP demand exceeds supply, creating metabolic stress, both KATP and ClC-1 channels are activated. KATP channels contribute to force reductions by lowering sarcolemmal generation of action potentials, whilst ClC-1 channel enhances the force-depressing effects of K+, thereby triggering fatigue. The ultimate function of these changes is to preserve the remaining ATP to prevent damaging ATP depletion.

Neurocirculatory regulation and adaptations to exercise in chronic kidney disease

Chronic kidney disease (CKD) is characterized by pronounced exercise intolerance and exaggerated blood pressure reactivity during exercise. Classic mechanisms of exercise intolerance in CKD have been extensively described previously and include uremic myopathy, chronic inflammation, malnutrition, and anemia. We contend that these classic mechanisms only partially explain the exercise intolerance experienced in CKD and that alterations in cardiovascular and autonomic regulation also play a key contributing role. The purpose of this review is to examine the physiological factors that contribute to neurocirculatory dysregulation during exercise and discuss the adaptations that result from regular exercise training in CKD. Key neurocirculatory mechanisms contributing to exercise intolerance in CKD include augmentation of the exercise pressor reflex, aberrations in neurocirculatory control, and increased neurovascular transduction. In addition, we highlight how some contributing factors may be improved through exercise training, with a specific focus on the sympathetic nervous system. Important areas for future work include understanding how the exercise prescription may best be optimized in CKD and how the beneficial effects of exercise training may extend to the brain.

Transcutaneous delivery of sodium bicarbonate increases intramuscular pH

Introduction: Oral bicarbonate loading improves the buffering of metabolic acidosis and may improve exercise performance but can also result in gastric distress. Momentous' PR Lotion contains a novel composition intended to provide a transdermal delivery vehicle for sodium bicarbonate which could allow the same ergogenic effect without the gastric distress. The present study explored the effect of transdermal delivery of sodium bicarbonate in a resting condition. Methods: We measured the pH from intramuscular dialysate, via microdialysis, of the vastus lateralis during a 2 h application of PR Lotion (40 g of lotion per leg) in 9 subjects (3 women, 6 men). Venous blood samples were obtained for serum pH before and after application. A placebo time control was also performed in 4 subjects (2 women, 2 men). We hypothesized that PR Lotion application would increase pH of intramuscular dialysate. Results: PR Lotion resulted in a rise in pH of 0.13 ± 0.04 units (p < 0.05), which translates to a 28% reduction in [H⁺]. Increases in serum pH were smaller (∼9%) yet consistent (p < 0.05). In contrast, placebo time control pH tended to decrease (p = 0.08). The effect of PR Lotion on pH tended to correlate with the dose per kg body weight of each individual (r = 0.70, p = 0.08). Conclusion: These observations support the idea of transdermal bicarbonate delivery impacting pH buffering both systemically and intramuscularly. Further work investigating these potential benefits in an exercising model would be critical to establishing PR Lotion's utility as an ergogenic aid.

Acute enteric-coated sodium bicarbonate has negligible effect on anaerobic performance but affects metabolomics and attenuates the gastrointestinal response

Sodium bicarbonate ingestion before exercise has a performance-enhancing effect on high-intensity exercise. However, gastrointestinal symptoms can be a problematic side-effect. Enteric-coated sodium bicarbonate can attenuate gastrointestinal symptoms following acute bicarbonate loading. In addition, the subsequent effects on exercise performance and metabolomics have not been investigated. The purpose of this study was to investigate the acute effect of enteric-coated sodium bicarbonate supplementation on the anaerobic performance, physiological profile, and symptoms of gastrointestinal discomfort after severe-intensity intermittent exercise. At the same time, targeted metabolomics was used to study the changes in urine metabolism after ingestion of enteric-coated sodium bicarbonate and to explore the characteristics of biological metabolism. In a randomized crossover design, twelve male college students completed four Wingate anaerobic 30-s cycling tests (WACT) after consuming a placebo (PL) and two experimental conditions: 0.2 g/kg body mass in enteric-coated sodium bicarbonate pills (ES) or general sodium bicarbonate pills (GS). Blood lactate (BLA), heart rate (HR), ratings of perceived exertion (RPE), and gastrointestinal–symptoms assessment questionnaire (GSAQ) were measured pre-exercise and post-exercise. In contrast, mean power (MP) and peak power (PP) were recorded immediately post-exercise. Urine samples were collected before formal tests and 50 min after the third WACT. Our findings indicate the following: 1) mean power and peak power showed no significant difference among conditions (MP: F_{2.0, 33} = 0.541, p = 0.587, η² = 0.032; PP: F_{2.0, 33} = 0.526, p = 0.596, η² = 0.031). The PP decline of the ES and GS after the third WACT was lower than that of the PL; 2) There were no significant differences in physiological responses, such as BLA (F_{2.0, 33.0}= 0.191, p = 0.827, η² = 0.011) and heart rate (F_{2, 33} = 0.418, p = 0.662, η² = 0.025), between the three conditions. Although blood lactate concentration after 10 min of the third WACT was lower with ES and GS than with placebo; 3) Fewer participants experienced gastrointestinal symptoms with enteric-coated than with general sodium bicarbonate; 4) The metabolites with differences among the three conditions 50 min after exercise were 3-phospho-d-glycerate, d-Glucose 6-phosphate, pyruvate, cis-aconitate, oxaloacetate, and citrate. ES had higher levels of 3-phospho-d-glycerate, d-Glucose 6-phosphate, pyruvate, and cis-aconitate than GS. The 3-phospho-d-glycerate, d-Glucose 6-phosphate, pyruvate, and cis-aconitate levels in GS were significantly lower than in PL. In contrast, the citrate level in GS was significantly higher than that in other experimental conditions. Compared to PL, the level of oxaloacetate was higher after exercise in ES. This data suggests that supplementation of enteric-coated and general sodium bicarbonate before exercise can alter energy metabolism following anaerobic exercise, involving the metabolism of 3-phospho-d-glycerate, D-Glucose 6-phosphate, pyruvate, cis-aconitate, oxaloacetate, citrate, and lactate. However, they do not affect anaerobic performance and blood lactate. The supplementation of acute enteric-coated sodium bicarbonate and general sodium bicarbonate can enhance some of the weak effects of blood lactate clearance during anaerobic exercise, which may be beneficial for glycolytic energy supply. In addition, enteric-coated sodium bicarbonate intake mitigates gastrointestinal symptoms compared to general sodium bicarbonate.

The peak force - resting membrane potential relationships of mouse fast- and slow-twitch muscle

We endeavored to understand the factors determining the peak force‑resting membrane potential (E_M) relationships of isolated slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles from mice (25^oC), especially in relation to fatigue. Inter-relationships between intracellular K⁺‑activity (aK⁺_i), extracellular K⁺‑concentration ([K⁺]_o), resting E_M, action potentials and force were studied. The large resting E_M variation was mainly due to the variability of aK⁺_i. Action potential overshoot‑resting E_M relationships determined at 4 and 8-10mM[K⁺]_o following short (<5min) and prolonged (>50min) depolarization periods revealed a constant overshoot from ‑90 to ‑70mV providing a safety margin. Overshoot decline with depolarization beyond ‑70mV was less following short than prolonged depolarization. Inexcitable fibers occurred only with prolonged depolarization. The overshoot decline during action potential trains (2‑s) exceeded that during short depolarizations. Concomitant lower extracellular [Na⁺] and raised [K⁺]_o depressed the overshoot in an additive manner and peak force in a synergistic manner. Raised [K⁺]_o-induced force loss was exacerbated with transverse wire versus parallel plate stimulation in soleus, implicating action potential propagation failure in the surface membrane. Increasing stimulus pulse parameters restored tetanic force at 9‑10mM[K⁺]_o in soleus, but not EDL, indicative of action potential failure within trains. The peak tetanic force‑resting E_M relationships (determined using resting E_M from deeper rather than surface fibers) were dynamic and show pronounced force depression over ‑69 to ‑60mV in both muscle-types, implicating that such depolarization contributes to fatigue. The K⁺-Na⁺-interaction shifted this relationship towards less depolarized potentials suggesting that the combined ionic effect is physiologically important during fatigue.

Extracellular Buffering Supplements to Improve Exercise Capacity and Performance: A Comprehensive Systematic Review and Meta-analysis

BACKGROUND

Extracellular buffering supplements [sodium bicarbonate (SB), sodium citrate (SC), sodium/calcium lactate (SL/CL)] are ergogenic supplements, although questions remain about factors which may modify their effect.

OBJECTIVE

To quantify the main effect of extracellular buffering agents on exercise outcomes, and to investigate the influence of potential moderators on this effect using a systematic review and meta-analytic approach.

METHODS

This study was designed in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Three databases were searched for articles that were screened according to inclusion/exclusion criteria. Bayesian hierarchical meta-analysis and meta-regression models were used to investigate pooled effects of supplementation and moderating effects of a range of factors on exercise and biomarker responses.

RESULTS

189 articles with 2019 participants were included, 158 involving SB supplementation, 30 with SC, and seven with CL/SL; four studies provided a combination of buffering supplements together. Supplementation led to a mean estimated increase in blood bicarbonate of + 5.2 mmol L^-1 (95% credible interval (CrI) 4.7-5.7). The meta-analysis models identified a positive overall effect of supplementation on exercise capacity and performance compared to placebo [ES_0.5 = 0.17 (95% CrI 0.12-0.21)] with potential moderating effects of exercise type and duration, training status and when the exercise test was performed following prior exercise. The greatest ergogenic effects were shown for exercise durations of 0.5-10 min [ES_0.5 = 0.18 (0.13-0.24)] and > 10 min [ES_0.5 = 0.22 (0.10-0.33)]. Evidence of greater effects on exercise were obtained when blood bicarbonate increases were medium (4-6 mmol L^-1) and large (> 6 mmol L^-1) compared with small (≤ 4 mmol L^-1) [β_Small:Medium = 0.16 (95% CrI 0.02-0.32), β_Small:Large = 0.13 (95% CrI - 0.03 to 0.29)]. SB (192 outcomes) was more effective for performance compared to SC (39 outcomes) [β_SC:SB = 0.10 (95% CrI - 0.02 to 0.22)].

CONCLUSIONS

Extracellular buffering supplements generate large increases in blood bicarbonate concentration leading to positive overall effects on exercise, with sodium bicarbonate being most effective. Evidence for several group-level moderating factors were identified. These data can guide an athlete's decision as to whether supplementation with buffering agents might be beneficial for their specific aims.

Serum electrolyte concentrations and skeletal muscle excitability in vivo

OBJECTIVE

Multi-fibre muscle velocity recovery cycle (MVRC) assessment is a well-tolerated method of evaluating sarcolemmal excitability in vivo that shows promise as a research tool and biomarker. MVRC parameters correlate with venous electrolyte concentrations in myopathies. We sought to determine the nature of any such relationships in individuals without muscle disease.

METHODS

Tibialis anterior MVRCs were recorded and electrolyte concentrations measured from two groups of healthy volunteers. After studying a single measure cohort (n = 65, one recording/person), we studied a repeated measures cohort (n = 4, eight recordings/person) to better study intra-individual relationships using repeated measures correlation (rmcorr).

RESULTS

In the single measure cohort, no significant correlations were present between MVRC parameters and electrolyte levels after accounting for age. In the repeated measures cohort, the relative refractory period (P < 0.01) and stimulus frequency measures (P < 0.01) correlated positively with potassium levels. Multiple late supernormality group measures correlated negatively with bicarbonate levels (P < 0.01).

CONCLUSIONS

MVRC measures that vary with the resting muscle membrane potential correlate with venous potassium concentrations, as in myopathies. Late supernormality measures correlate with bicarbonate levels.

SIGNIFICANCE

Determination of serum electrolyte levels may inform the interpretation of MVRC study results if variation in concentrations is anticipated to be significant.

International Society of Sports Nutrition position stand: sodium bicarbonate and exercise performance

Based on a comprehensive review and critical analysis of the literature regarding the effects of sodium bicarbonate supplementation on exercise performance, conducted by experts in the field and selected members of the International Society of Sports Nutrition (ISSN), the following conclusions represent the official Position of the Society: 1. Supplementation with sodium bicarbonate (doses from 0.2 to 0.5 g/kg) improves performance in muscular endurance activities, various combat sports, including boxing, judo, karate, taekwondo, and wrestling, and in high-intensity cycling, running, swimming, and rowing. The ergogenic effects of sodium bicarbonate are mostly established for exercise tasks of high-intensity that last between 30 s and 12 min. 2. Sodium bicarbonate improves performance in single- and multiple-bout exercise. 3. Sodium bicarbonate improves exercise performance in both men and women. 4. For single-dose supplementation protocols, 0.2 g/kg of sodium bicarbonate seems to be the minimum dose required to experience improvements in exercise performance. The optimal dose of sodium bicarbonate dose for ergogenic effects seems to be 0.3 g/kg. Higher doses (e.g., 0.4 or 0.5 g/kg) may not be required in single-dose supplementation protocols, because they do not provide additional benefits (compared with 0.3 g/kg) and are associated with a higher incidence and severity of adverse side-effects. 5. For single-dose supplementation protocols, the recommended timing of sodium bicarbonate ingestion is between 60 and 180 min before exercise or competition. 6. Multiple-day protocols of sodium bicarbonate supplementation can be effective in improving exercise performance. The duration of these protocols is generally between 3 and 7 days before the exercise test, and a total sodium bicarbonate dose of 0.4 or 0.5 g/kg per day produces ergogenic effects. The total daily dose is commonly divided into smaller doses, ingested at multiple points throughout the day (e.g., 0.1 to 0.2 g/kg of sodium bicarbonate consumed at breakfast, lunch, and dinner). The benefit of multiple-day protocols is that they could help reduce the risk of sodium bicarbonate-induced side-effects on the day of competition. 7. Long-term use of sodium bicarbonate (e.g., before every exercise training session) may enhance training adaptations, such as increased time to fatigue and power output. 8. The most common side-effects of sodium bicarbonate supplementation are bloating, nausea, vomiting, and abdominal pain. The incidence and severity of side-effects vary between and within individuals, but it is generally low. Nonetheless, these side-effects following sodium bicarbonate supplementation may negatively impact exercise performance. Ingesting sodium bicarbonate (i) in smaller doses (e.g., 0.2 g/kg or 0.3 g/kg), (ii) around 180 min before exercise or adjusting the timing according to individual responses to side-effects, (iii) alongside a high-carbohydrate meal, and (iv) in enteric-coated capsules are possible strategies to minimize the likelihood and severity of these side-effects. 9. Combining sodium bicarbonate with creatine or beta-alanine may produce additive effects on exercise performance. It is unclear whether combining sodium bicarbonate with caffeine or nitrates produces additive benefits. 10. Sodium bicarbonate improves exercise performance primarily due to a range of its physiological effects. Still, a portion of the ergogenic effect of sodium bicarbonate seems to be placebo-driven.

Skeletal muscle phenotype and game performance in elite women football players

We combined game activity analyses with skeletal muscle phenotypes and comprehensive physiological testing to elucidate factors of importance for physical performance in elite women's football. GPS-data from an experimental game, sprint and endurance testing, and muscle tissue analysis of metabolic enzyme activity, protein expression and fiber type composition were completed for international top-level women players (n = 20; age; 23 ± 4 yrs, height; 166 ± 10 cm, weight; 60 ± 8 kg; VO_2max ; 51 ± 6 ml/min/kg). Muscle monocarboxylate transporter 4 (MCT4) protein expression explained 46% of the variance in total game distance, while the ability to maintain high-intensity running (HIR) during the final 15 min of the game correlated to myosin heavy chain 1 (MHCI) and Na⁺ -K⁺ ATPase β1, FXYD1 (phospholemman) and superoxide dismutase 2 (SOD2) protein expression (range: r = 0.51-0.71; all p < 0.05). Total HIR distance correlated with (MHCIIa) protein expression (r = 0.51; p < 0.05), while muscle Na⁺ /H⁺ exchanger 1 (NHE1) protein explained 36% of the variance in game sprint distance (p < 0.05). Total game accelerations (actions >4 m/s² ) correlated with platelet endothelial cell adhesion molecule (PECAM-1) protein expression (r = 0.51; p < 0.05), while concentric knee flexor strength explained 42-62% of the variance in intense decelerations (>4 m/s² ). In conclusion, for elite women players' game endurance performance and resistance to end-game fatigue were affected by monocarboxylate transporter expression and myosin heavy chain profile. HIR was also correlated to ion transporter expression and muscle antioxidative capacity. Finally, the importance of functional strength and measures of muscle vascularization in relation to total game decelerations and accelerations, respectively, illustrates the complex physiological demands in elite women's football.

The time to peak blood bicarbonate (HCO3-), pH, and the strong ion difference (SID) following sodium bicarbonate (NaHCO3) ingestion in highly trained adolescent swimmers

The timing of sodium bicarbonate (NaHCO₃) supplementation has been suggested to be most optimal when coincided with a personal time that bicarbonate (HCO₃^–) or pH peaks in the blood following ingestion. However, the ergogenic mechanisms supporting this ingestion strategy are strongly contested. It is therefore plausible that NaHCO₃ may be ergogenic by causing beneficial shifts in the strong ion difference (SID), though the time course of this blood acid base balance variable is yet to be investigated. Twelve highly trained, adolescent swimmers (age: 15.9 ± 1.0 years, body mass: 65.3 ± 9.6 kg) consumed their typical pre-competition nutrition 1–3 hours before ingesting 0.3 g∙kg BM^-1 NaHCO₃ in gelatine capsules. Capillary blood samples were then taken during seated rest on nine occasions (0, 60, 75, 90, 105, 120, 135, 150, 165 min post-ingestion) to identify the time course changes in HCO₃^–, pH, and the SID. No significant differences were found in the time to peak of each blood measure (HCO₃^–: 130 ± 35 min, pH: 120 ± 38 min, SID: 98 ± 37 min; p = 0.08); however, a large effect size was calculated between time to peak HCO₃^– and the SID (g = 0.88). Considering that a difference between time to peak blood HCO₃^– and the SID was identified in adolescents, future research should compare the ergogenic effects of these two individualized NaHCO₃ ingestion strategies compared to a traditional, standardized approach.

Muscle Ionic Shifts During Exercise: Implications for Fatigue and Exercise Performance

Exercise causes major shifts in multiple ions (e.g., K⁺ , Na⁺ , H⁺ , lactate^- , Ca²⁺ , and Cl^- ) during muscle activity that contributes to development of muscle fatigue. Sarcolemmal processes can be impaired by the trans-sarcolemmal rundown of ion gradients for K⁺ , Na⁺ , and Ca²⁺ during fatiguing exercise, while changes in gradients for Cl^- and Cl^- conductance may exert either protective or detrimental effects on fatigue. Myocellular H⁺ accumulation may also contribute to fatigue development by lowering glycolytic rate and has been shown to act synergistically with inorganic phosphate (Pi) to compromise cross-bridge function. In addition, sarcoplasmic reticulum Ca²⁺ release function is severely affected by fatiguing exercise. Skeletal muscle has a multitude of ion transport systems that counter exercise-related ionic shifts of which the Na⁺ /K⁺ -ATPase is of major importance. Metabolic perturbations occurring during exercise can exacerbate trans-sarcolemmal ionic shifts, in particular for K⁺ and Cl^- , respectively via metabolic regulation of the ATP-sensitive K⁺ channel (K_ATP ) and the chloride channel isoform 1 (ClC-1). Ion transport systems are highly adaptable to exercise training resulting in an enhanced ability to counter ionic disturbances to delay fatigue and improve exercise performance. In this article, we discuss (i) the ionic shifts occurring during exercise, (ii) the role of ion transport systems in skeletal muscle for ionic regulation, (iii) how ionic disturbances affect sarcolemmal processes and muscle fatigue, (iv) how metabolic perturbations exacerbate ionic shifts during exercise, and (v) how pharmacological manipulation and exercise training regulate ion transport systems to influence exercise performance in humans. © 2021 American Physiological Society. Compr Physiol 11:1895-1959, 2021.

Evaluation of High-Intensity Interval Training and Beta-Alanine Supplementation on Efficiency of Electrical Activity and Electromyographic Fatigue Threshold

ABSTRACT

Herda, AA, Smith-Ryan, AE, Kendall, KL, Cramer, JT, and Stout, JR. Evaluation of high-intensity interval training and beta-alanine supplementation on efficiency of electrical activity and electromyographic fatigue threshold. J Strength Cond Res 35(6): 1535-1541, 2021-The purpose of this study was to determine the effects of high-intensity interval training (HIIT) with or without β-alanine (BA) supplementation on the electromyographic fatigue threshold (EMGFT) and efficiency of electrical activity (EEA) in young women. Forty-four women (mean ± SD; age [yrs]: 21.7 ± 3.7; height [cm]: 166.3 ± 6.4; body mass [kg]: 66.1 ± 10.3) were randomly assigned to one of 3 treatment groups. The supplement groups performed HIIT on the cycle ergometer 3 times·wk-1 for 6 weeks. Electromyographic fatigue threshold and EEA were assessed at baseline (PRE), after 3 weeks of training (MID), and after 6 weeks of HIIT (POST). Two 2-way mixed factorial analyses of variance (time [PRE vs. MID vs. POST] × treatment (BA vs. PL vs. CON)] were used to analyze EMGFT and EEA with a predetermined level of significance α of 0.05. For EMGFT, there was no interaction (p = 0.26) and no main effect for time (p = 0.28) nor treatment (p = 0.86); thus, there were no changes in EMGFT regardless of training or supplementation status. For EEA, there was no interaction (p = 0.70) nor treatment (p = 0.79); however, there was a main effect for time (p < 0.01). Our findings indicated that neither training nor supplementation was effective in improving EMGFT in women. Efficiency of electrical activity was altered, potentially because of a learning effect. Coaches and practitioners may not use these tests to monitor training status; however, they may find EEA as a useful tool to track cycling efficiency.

Does varying the ingestion period of sodium citrate influence blood alkalosis and gastrointestinal symptoms?

OBJECTIVES

To compare blood alkalosis, gastrointestinal symptoms and indicators of strong ion difference after ingestion of 500 mg.kg-1 BM sodium citrate over four different periods.

METHODS

Sixteen healthy and active participants ingested 500 mg.kg-1 BM sodium citrate in gelatine capsules over a 15, 30, 45 or 60 min period using a randomized cross-over experimental design. Gastrointestinal symptoms questionnaires and venous blood samples were collected before ingestion, immediately post-ingestion, and every 30 min for 480 min post-ingestion. Blood samples were analysed for blood pH, [HCO3-], [Na+], [Cl-] and plasma [citrate]. Linear mixed models were used to estimate the effect of the ingestion protocols.

RESULTS

For all treatments, blood [HCO3-] was significantly elevated above baseline for the entire 480 min post-ingestion period, and peak occurred 180 min post-ingestion. Blood [HCO3-] and pH were significantly elevated above baseline and not significantly below the peak between 150-270 min post-ingestion. Furthermore, blood pH and [HCO3-] were significantly lower for the 60 min ingestion period when compared to the other treatments. Gastrointestinal symptoms were minor for all treatments; the mean total session symptoms ratings (all times summed together) were between 9.8 and 11.6 from a maximum possible rating of 720.

CONCLUSION

Based on the findings of this investigation, sodium citrate should be ingested over a period of less than 60 min (15, 30 or 45 min), and completed 150-270 min before exercise.

Factors Influencing Blood Alkalosis and Other Physiological Responses, Gastrointestinal Symptoms, and Exercise Performance Following Sodium Citrate Supplementation: A Review

This review aimed to identify factors associated with (a) physiological responses, (b) gastrointestinal (GI) symptoms, and (c) exercise performance following sodium citrate supplementation. A literature search identified 33 articles. Observations of physiological responses and GI symptoms were categorized by dose (< 500, 500, and > 500 mg/kg body mass [BM]) and by timing of postingestion measurements (in minutes). Exercise performance following sodium citrate supplementation was compared with placebo using statistical significance, percentage change, and effect size. Performance observations were categorized by exercise duration (very short < 60 s, short ≥ 60 and ≤ 420 s, and longer > 420 s) and intensity (very high > 100% VO2max and high 90-100% VO2max). Ingestion of 500 mg/kg BM sodium citrate induced blood alkalosis more frequently than < 500 mg/kg BM, and with similar frequency to >500 mg/kg BM. The GI symptoms were minimized when a 500 mg/kg BM dose was ingested in capsules rather than in solution. Significant improvements in performance following sodium citrate supplementation were reported in all observations of short-duration and very high-intensity exercise with a 500 mg/kg BM dose. However, the efficacy of supplementation for short-duration, high-intensity exercise is less clear, given that only 25% of observations reported significant improvements in performance following sodium citrate supplementation. Based on the current literature, the authors recommend ingestion of 500 mg/kg BM sodium citrate in capsules to induce alkalosis and minimize GI symptoms. Supplementation was of most benefit to performance of short-duration exercise of very high intensity; further investigation is required to determine the importance of ingestion duration and timing.

Regulation of muscle potassium: exercise performance, fatigue and health implications

This review integrates from the single muscle fibre to exercising human the current understanding of the role of skeletal muscle for whole-body potassium (K⁺) regulation, and specifically the regulation of skeletal muscle [K⁺]. We describe the K⁺ transport proteins in skeletal muscle and how they contribute to, or modulate, K⁺ disturbances during exercise. Muscle and plasma K⁺ balance are markedly altered during and after high-intensity dynamic exercise (including sports), static contractions and ischaemia, which have implications for skeletal and cardiac muscle contractile performance. Moderate elevations of plasma and interstitial [K⁺] during exercise have beneficial effects on multiple physiological systems. Severe reductions of the trans-sarcolemmal K⁺ gradient likely contributes to muscle and whole-body fatigue, i.e. impaired exercise performance. Chronic or acute changes of arterial plasma [K⁺] (hyperkalaemia or hypokalaemia) have dangerous health implications for cardiac function. The current mechanisms to explain how raised extracellular [K⁺] impairs cardiac and skeletal muscle function are discussed, along with the latest cell physiology research explaining how calcium, β-adrenergic agonists, insulin or glucose act as clinical treatments for hyperkalaemia to protect the heart and skeletal muscle in vivo. Finally, whether these agents can also modulate K⁺-induced muscle fatigue are evaluated.

Effects of endurance exercise under hypoxia on acid-base and ion balance in healthy males

[Purpose]

This study was performed to investigate the acid-base and ion balance at rest and after exercise in healthy males under normoxia, moderate hypoxia, and severe hypoxia.

[Methods]

Ten healthy Korean males completed three different trials on different days, comprising exercise under normoxia (F_iO₂ = 20.9%, N trial), moderate hypoxia (F_iO₂ = 16.5%, MH trial), and severe hypoxia (F_iO₂ = 12.8%, SH trial). They undertook endurance exercise for 30 min on a cycle ergometer at the same relative exercise intensity equivalent to 80% maximal heart rate under all conditions. Capillary blood samples were obtained to determine acid-base and ion balance at rest and after exercise.

[Results]

Exercise-induced blood lactate elevations were significantly increased as hypoxic conditions became more severe; SH > MH > N trials (P = 0.003). After exercise, blood glucose levels were significantly higher in the SH trial than in the N and MH trials (P = 0.001). Capillary oxygen saturation (S_CO₂) levels were significantly lowered as hypoxic conditions became more severe; SH > MH > N trials (P < 0.001). The pH levels were significantly lower in the MH trial than that in the N trial (P = 0.010). Moreover, H_CO₃- levels were significantly lower in the SH trial than in the N trial, with significant interaction (P = 0.003). There were no significant differences in blood Na⁺, K⁺, and Ca²⁺ levels between the trials.

[Conclusion]

MH and SH trials induced greater differences in glucose, lactate, S_CO₂, pH, and H_CO₃- levels in capillary blood compared to the N trial. Additionally, lactate, S_CO₂, and H_CO₃- levels showed greater changes in the SH trial than in the MH trial. However, there were no significant differences in Na⁺, K⁺, and Ca²⁺ levels in MH and SH trials compared to the N trial.

Skeletal muscle energy metabolism during exercise

The continual supply of ATP to the fundamental cellular processes that underpin skeletal muscle contraction during exercise is essential for sports performance in events lasting seconds to several hours. Because the muscle stores of ATP are small, metabolic pathways must be activated to maintain the required rates of ATP resynthesis. These pathways include phosphocreatine and muscle glycogen breakdown, thus enabling substrate-level phosphorylation ('anaerobic') and oxidative phosphorylation by using reducing equivalents from carbohydrate and fat metabolism ('aerobic'). The relative contribution of these metabolic pathways is primarily determined by the intensity and duration of exercise. For most events at the Olympics, carbohydrate is the primary fuel for anaerobic and aerobic metabolism. Here, we provide an overview of exercise metabolism and the key regulatory mechanisms ensuring that ATP resynthesis is closely matched to the ATP demand of exercise. We also summarize various interventions that target muscle metabolism for ergogenic benefit in athletic events.

Dietary Acid-Base Balance in High-Performance Athletes

Physical exercise leads to metabolic changes that affect the acid-base balance in skeletal muscles and other tissues. Nutrition is one of the factors that may influence the acid-base balance in the body. Keeping alkaline circumstances in the body is important not only for health and athletic performance in training but also during competition in many sport events. This is especially significant for athletes who practice in sport at the highest level of competition. The aim of the study was to determine the dietary acid-base balance in competitive Lithuanian high-performance athletes, and to evaluate the effect of actual diets of athletes on NEAP (net endogenous acid production), muscle mass and body mineral content during a four-year Olympic cycle. The research participants were 18.1 ± 3.3-year-old Lithuanian high performance athletes (n = 323). The actual diet was investigated using the 24 h recall dietary survey method. The measurements of body composition were performed using BIA (bioelectrical impedance analysis). The potential renal acid load of the diets of athletes (dietary PRAL) and NEAP were calculated. In 10.2% of athletes, NEAP exceeds 100 mEq · day-1 and is on average 126.1 ± 32.7 mEq · day-1. Higher NEAP in athletes is associated with lower muscle mass (β -1.2% of body weight, p < 0.001) but has no effect on the amount of minerals in the body (β 0.01% of body weight, p = 0.073). Overall, 25-30% of Lithuanian high-performance athletes use high-protein diets (2.0-4.8 g · kg-1 · day-1) leading to a dietary acid-base imbalance as well as an excessive production of endogenous acids in the body. Athletes are recommended to consume higher amounts of potassium and magnesium. An increase in calcium intake up to 1500 mg per day is recommended. In exceptional cases, periodised nutrition for athletes may involve diets complemented with bicarbonate and/or beta-alanine supplements.

Exercise Training, Intermittent Fasting and Alkaline Supplementation as an Effective Strategy for Body Weight Loss: A 12-Week Placebo-Controlled Double-Blind Intervention with Overweight Subjects

BACKGROUND

Intermittent fasting (IF) combined with exercise has been suggested to enhance weight loss. However, both procedures might negatively influence acid-base status. The aim of this study was to determine the combined effects of IF, exercise training and alkaline supplementation in overweight subjects on body composition and running performance.

METHODS

80 overweight subjects of age 45.5 ± 7.8 years were assigned to IF or non-intermittent fasting (nIF). Furthermore, subjects were randomly assigned to take either an alkaline supplement (IF-v, nIF-v) or a placebo (IF-p, nIF-p) twice a day. All subjects performed a personalized endurance exercise program (3-4 times/week for 12 weeks). Body weight, body composition, running performance and acid-base parameters were determined before (pre) and after the 12-week program (post).

RESULTS

68 participants completed the study. There was a significant effect on body weight loss, body fat loss, visceral fat loss and running performance enhancement in all groups (p < 0.01) for pre and post measurements. Body weight decreased in all groups (IF-p: -5.80 ± 0.77 kg and nIF-p: -3.40 ± 0.58 kg; IF-v: -8.28 ± 0.75 kg and nIF-v: -5.59 ± 0.87 kg). In both dietary strategies, weight loss was significantly further enhanced by alkaline supplementation. The increase in running velocity was significantly higher in IF combined with alkaline supplementation (IF-v 1.73 ± 0.23 km/h and IF-p 0.97 ± 0.20 km/h). In addition, alkaline supplementation increased plasma HCO₃^- concentration and urinary pH.

CONCLUSION

Exercise training in combination with IF and alkaline supplementation is an effective strategy to reduce body weight and improve running performance in a 12-week intervention.

KIR channel activation links local vasodilatation with muscle fibre recruitment during exercise in humans

KEY POINTS

During exercise, blood flow to working skeletal muscle increases in parallel with contractile activity such that oxygen delivery is sufficient to meet metabolic demand. K⁺ released from active skeletal muscle fibres could facilitate vasodilatation in proportion to the degree of muscle fibre recruitment. Once released, K⁺ stimulates inwardly rectifying K⁺ (K_IR ) channels on the vasculature to elicit an increase in blood flow. In the present study, we demonstrate that K_IR channels mediate the rapid vasodilatory response to an increase in exercise intensity. We also show that K_IR channels augment vasodilatation during exercise which demands greater muscle fibre recruitment independent of the total amount of work performed. These results suggest that K⁺ plays a key role in coupling the magnitude of vasodilatation to the degree of contractile activity. Ultimately, the findings from this study help us understand the signalling mechanisms that regulate muscle blood flow in humans.

ABSTRACT

Blood flow to active skeletal muscle is augmented with greater muscle fibre recruitment. We tested whether activation of inwardly rectifying potassium (K_IR ) channels underlies vasodilatation with elevated muscle fibre recruitment when work rate is increased (Protocol 1) or held constant (Protocol 2). We assessed forearm vascular conductance (FVC) during rhythmic handgrip exercise under control conditions and during local inhibition of K_IR channels (intra-arterial BaCl₂ ). In Protocol 1, healthy volunteers performed mild handgrip exercise for 3 min, then transitioned to moderate intensity for 30 s. BaCl₂ eliminated vasodilatation during the first contraction at the moderate workload (ΔFVC, BaCl₂ : -1 ± 17 vs. control: 30 ± 28 ml min^-1  100 mmHg^-1 ; n = 9; P = 0.004) and attenuated the 30 s area under the curve by 56 ± 14% (n = 9; P < 0.0001). In Protocol 2, participants performed two exercise bouts in which muscle fibre recruitment was manipulated while total contractile work was held constant via reciprocal changes in contraction frequency: (1) low fibre recruitment, with contractions at 12.5% maximal voluntary contraction once every 4 s and (2) high fibre recruitment, with contractions at 25% maximal voluntary contraction once every 8 s. Under control conditions, steady-state FVC was augmented in high vs. low fibre recruitment (211 ± 90 vs. 166 ± 73 ml min^-1 ⋅100 mmHg^-1 ; n = 10; P = 0.0006), whereas BaCl₂ abolished the difference between high and low fibre recruitment (134 ± 59 vs. 134 ± 63 ml min^-1  100 mmHg^-1 ; n = 10; P = 0.85). These findings demonstrate that K_IR channel activation is a key mechanism linking local vasodilatation with muscle fibre recruitment during exercise.

The Effects of Endurance Exercise in Hypoxia on Acid-Base Balance, Potassium Kinetics, and Exogenous Glucose Oxidation

Purpose

To investigate the carbohydrate metabolism, acid–base balance, and potassium kinetics in response to exercise in moderate hypoxia among endurance athletes.

Methods

Nine trained endurance athletes [maximal oxygen uptake (VO_2max): 62.5 ± 1.2 mL/kg/min] completed two different trials on different days: either exercise in moderate hypoxia [fraction of inspired oxygen (FiO₂) = 14.5%, HYPO] or exercise in normoxia (FiO₂ = 20.9%, NOR). They performed a high-intensity interval-type endurance exercise consisting of 10 × 3 min runs at 90% of VO_2max with 60 s of running (active rest) at 50% of VO_2max between sets in hypoxia (HYPO) or normoxia (NOR). Venous blood samples were obtained before exercise and during the post-exercise. The subjects consumed ¹³C-labeled glucose immediately before exercise, and we collected expired gas samples during exercise to determine the ¹³C-excretion (calculated as ¹³CO₂/¹²CO₂).

Results

The running velocities were significantly lower in HYPO (15.0 ± 0.2 km/h) than in NOR (16.4 ± 0.3 km/h, P < 0.0001). Despite the lower running velocity, we found a significantly greater exercise-induced blood lactate elevation in HYPO compared with in NOR (P = 0.002). The bicarbonate ion concentration (P = 0.002) and blood pH (P = 0.002) were significantly lower in HYPO than in NOR. There were no significant differences between the two trials regarding the exercise-induced blood potassium elevation (P = 0.87) or ¹³C-excretion (HYPO, 0.21 ± 0.02 mmol⋅39 min; NOR, 0.14 ± 0.03 mmol⋅39 min; P = 0.10).

Conclusion

Endurance exercise in moderate hypoxia elicited a decline in blood pH. However, it did not augment the exercise-induced blood K⁺ elevation or exogenous glucose oxidation (¹³C-excretion) compared with the equivalent exercise in normoxia among endurance athletes. The findings suggest that endurance exercise in moderate hypoxia causes greater metabolic stress and similar exercise-induced elevation of blood K⁺ and exogenous glucose oxidation compared with the same exercise in normoxia, despite lower mechanical stress (i.e., lower running velocity).

Characterization of the Human Skeletal Muscle Metabolome for Elucidating the Mechanisms of Bicarbonate Ingestion on Strenuous Interval Exercise

Bicarbonate has long been touted as a putative ergogenic aid that improves exercise performance and blood buffering capacity during strenuous exercise. However, the underlying mechanisms of action of bicarbonate intake on skeletal muscle metabolism have yet to be fully elucidated. Herein, we apply two orthogonal analytical platforms for nontargeted profiling of metabolites and targeted analysis of electrolytes from mass-limited muscle tissue biopsies (∼2 mg dried mass) when multisegment injection-capillary electrophoresis-mass spectrometry (MSI-CE-MS) and CE with indirect UV detection are used, respectively. Seven untrained men performed a standardized bout of high-intensity interval exercise trial following either bicarbonate (0.40 g/kg) or placebo ingestion in a double-blinded, placebo-controlled, crossover study design, where paired skeletal muscle tissue and plasma specimens were collected at three time intervals at rest, postexercise, and recovery. Optimization of a quantitative microextraction procedure was first developed for lyophilized tissue prior to characterization of the human muscle metabolome, which resulted in the identification and quantification of more than 80 polar/ionic metabolites reliably (CV < 30%) detected in a majority (>75%) of samples with quality control. Complementary univariate and multivariate statistical methods were used to identify biomarkers associated with strenuous exercise and/or bicarbonate treatment responses, whereas structural elucidation of biologically significant intramuscular metabolites was performed using high-resolution MS/MS. Importantly, bicarbonate ingestion prior to strenuous interval exercise was found to elicit a modest treatment effect ( p < 0.05) in comparison to placebo on metabolic pathways associated with ionic homeostasis (potassium), purine degradation (uric acid), and oxidative stress as regulated by glutathione metabolism (oxidized mixed glutathione disulfide) and histidine-containing dipeptides (anserine) within muscle tissue that was distinctive from dynamic metabolic changes measured in circulation. This work provides deeper biochemical insights into the effect of acute alkalosis in preserving contracting muscle function during high-intensity exercise, which is also applicable to the study of muscle-related pathologies relevant to human health and aging.

Molecular stressors underlying exercise training-induced improvements in K+ regulation during exercise and Na+ ,K+ -ATPase adaptation in human skeletal muscle

Despite substantial progress made towards a better understanding of the importance of skeletal muscle K⁺ regulation for human physical function and its association with several disease states (eg type-II diabetes and hypertension), the molecular basis underpinning adaptations in K⁺ regulation to various stimuli, including exercise training, remains inadequately explored in humans. In this review, the molecular mechanisms essential for enhancing skeletal muscle K⁺ regulation and its key determinants, including Na⁺ ,K⁺ -ATPase function and expression, by exercise training are examined. Special attention is paid to the following molecular stressors and signaling proteins: oxygenation, redox balance, hypoxia, reactive oxygen species, antioxidant function, Na⁺ ,K⁺ , and Ca²⁺ concentrations, anaerobic ATP turnover, AMPK, lactate, and mRNA expression. On this basis, an update on the effects of different types of exercise training on K⁺ regulation in humans is provided, focusing on recent discoveries about the muscle fibre-type-dependent regulation of Na⁺ ,K⁺ -ATPase-isoform expression. Furthermore, with special emphasis on blood-flow-restricted exercise as an exemplary model to modulate the key molecular mechanisms identified, it is discussed how training interventions may be designed to maximize improvements in K⁺ regulation in humans. The novel insights gained from this review may help us to better understand how exercise training and other strategies, such as pharmacological interventions, may be best designed to enhance K⁺ regulation and thus the physical function in humans.

The effects of endurance exercise in hypoxia on acid-base balance and potassium kinetics: a randomized crossover design in male endurance athletes

Background

Exercise-induced disturbance of acid-base balance and accumulation of extracellular potassium (K⁺) are suggested to elicit fatigue. Exercise under hypoxic conditions may augment exercise-induced alterations of these two factors compared with exercise under normoxia. In the present study, we investigated acid-base balance and potassium kinetics in response to exercise under moderate hypoxic conditions in endurance athletes.

Methods

Nine trained middle-to-long distance athletes [maximal oxygen uptake (VO_2max) 57.2 ± 1.0 mL/kg/min] completed two different trials on different days, consisting of exercise in moderate hypoxia [fraction of inspired oxygen (F_iO₂) = 14.5%, H trial] and exercise in normoxia (F_iO₂ = 20.9%, N trial). They performed interval endurance exercise (8 × 4 min pedaling at 80% of VO_2max alternated with 2-min intervals of active rest at 40% of VO_2max) under hypoxic or normoxic conditions. Venous blood samples were obtained to determine blood lactate, pH, bicarbonate ion, and K⁺ concentrations before exercise, during exercise, and after exercise.

Results

The blood lactate concentrations increased significantly with exercise in both trials. Exercise-induced blood lactate elevations were significantly greater in the N trial than in the H trial at all time points (P = 0.012). Bicarbonate ion concentrations (P = 0.001) and blood pH (P = 0.019) during exercise and post-exercise periods were significantly lower in the N trial than in the H trial. A significantly greater exercise-induced elevation in blood K⁺ concentration was produced in the N trial than in the H trial during exercise and immediately after exercise (P = 0.03).

Conclusions

High-intensity interval exercise on a cycle ergometer under moderate hypoxic conditions did not elicit a decrease in blood pH or elevation in K⁺ levels compared with an equivalent level of exercise under normoxic conditions.

β-Alanine Supplementation's Improvement of High-Intensity Game Activities in Water Polo

OBJECTIVES

To investigate whether 4 wk of β-alanine supplementation improves total distance covered, distance covered and time spent in different speed zones, and sprint numbers during a simulated water polo game.

DESIGN

Double-blind, parallel, and placebo controlled. A total of 11 male water polo players participated in the study, divided randomly into 2 homogeneous groups (placebo and β-alanine).

METHODS

The participants performed a simulated water polo game before and after the supplementation period (4 wk). They received 4.8 g·d^-1 of dextrose or β-alanine on the first 10 d and 6.4 g·d^-1 on the final 18 d.

RESULTS

Only the β-alanine group presented a significant improvement in total sprint numbers compared with the presupplementation moment (PRE = 7.8 [5.2] arbitrary units [a.u.]; POST = 20.2 [7.8] a.u.; P = .002). Furthermore, β-alanine supplementation presented a likely beneficial effect in improving total distance covered (83%) and total time spent (81%) in speed zone 4 (ie, speed ≥ 1.8 m·s^-1). There was no significant interaction effect (group × time) for any variable.

CONCLUSIONS

Four weeks of β-alanine supplementation slightly improved sprint numbers and had a likely beneficial effect on improving distance covered and time spent in speed zone 4 in a simulated water polo game.

Enhanced 400-m sprint performance in moderately trained participants by a 4-day alkalizing diet: a counterbalanced, randomized controlled trial

Background

Sodium bicarbonate (NaHCO₃) is an alkalizing agent and its ingestion is used to improve anaerobic performance. However, the influence of alkalizing nutrients on anaerobic exercise performance remains unclear. Therefore, the present study investigated the influence of an alkalizing versus acidizing diet on 400-m sprint performance, blood lactate, blood gas parameters, and urinary pH in moderately trained adults.

Methods

In a randomized crossover design, eleven recreationally active participants (8 men, 3 women) aged 26.0 ± 1.7 years performed one trial under each individual’s unmodified diet and subsequently two trials following either 4 days of an alkalizing (BASE) or acidizing (ACID) diet. Trials consisted of 400-m runs at intervals of 1 week on a tartan track in a randomized order.

Results

We found a significantly lower 400-m performance time for the BASE trial (65.8 ± 7.2 s) compared with the ACID trial (67.3 ± 7.1 s; p = 0.026). In addition, responses were significantly higher following the BASE diet for blood lactate (BASE: 16.3 ± 2.7; ACID: 14.4 ± 2.1 mmol/L; p = 0.32) and urinary pH (BASE: 7.0 ± 0.7; ACID: 5.5 ± 0.7; p = 0.001).

Conclusions

We conclude that a short-term alkalizing diet may improve 400-m performance time in moderately trained participants. Additionally, we found higher blood lactate concentrations under the alkalizing diet, suggesting an enhanced blood or muscle buffer capacity. Thus, an alkalizing diet may be an easy and natural way to enhance 400-m sprint performance for athletes without the necessity of taking artificial dietary supplements.

Elevated extracellular potassium prior to muscle contraction reduces onset and steady-state exercise hyperemia in humans

The increase in interstitial potassium (K⁺) during muscle contractions is thought to be a vasodilatory signal that contributes to exercise hyperemia. To determine the role of extracellular K⁺ in exercise hyperemia, we perfused skeletal muscle with K⁺ before contractions, such that the effect of any endogenously-released K⁺ would be minimized. We tested the hypothesis that local, intra-arterial infusion of potassium chloride (KCl) at rest would impair vasodilation in response to subsequent rhythmic handgrip exercise in humans. In 11 young adults, we determined forearm blood flow (FBF) (Doppler ultrasound) and forearm vascular conductance (FVC) (FBF/mean arterial pressure) during 4 min of rhythmic handgrip exercise at 10% of maximal voluntary contraction during 1) control conditions, 2) infusion of KCl before the initiation of exercise, and 3) infusion of sodium nitroprusside (SNP) as a control vasodilator. Infusion of KCl or SNP elevated resting FVC similarly before the onset of exercise (control: 39 ± 6 vs. KCl: 81 ± 12 and SNP: 82 ± 13 ml·min^-1·100 mmHg^-1; both P < 0.05 vs. control). Infusion of KCl at rest diminished the hyperemic (ΔFBF) and vasodilatory (ΔFVC) response to subsequent exercise by 22 ± 5% and 30 ± 5%, respectively (both P < 0.05 vs. control), whereas SNP did not affect the change in FBF ( P = 0.74 vs. control) or FVC ( P = 0.61 vs. control) from rest to steady-state exercise. These findings implicate the K⁺ ion as an essential vasodilator substance contributing to exercise hyperemia in humans. NEW & NOTEWORTHY Our findings support a significant and obligatory role for potassium signaling in the local vasodilatory and hyperemic response to exercise in humans.

Improved Exercise Tolerance with Caffeine Is Associated with Modulation of both Peripheral and Central Neural Processes in Human Participants

Background

Caffeine has been shown to enhance exercise performance and capacity. The mechanisms remain unclear but are suggested to relate to adenosine receptor antagonism, resulting in increased central motor drive, reduced perception of effort, and altered peripheral processes such as enhanced calcium handling and extracellular potassium regulation. Our aims were to investigate how caffeine (i) affects knee extensor PCr kinetics and pH during repeated sets of single-leg knee extensor exercise to task failure and (ii) modulates the interplay between central and peripheral neural processes. We hypothesized that the caffeine-induced extension of exercise capacity during repeated sets of exercise would occur despite greater disturbance of the muscle milieu due to enhanced peripheral and corticospinal excitatory output, central motor drive, and muscle contractility.

Methods

Nine healthy active young men performed five sets of intense single-leg knee extensor exercise to task failure on four separate occasions: for two visits (6 mg·kg^-1 caffeine vs placebo), quadriceps ³¹P-magnetic resonance spectroscopy scans were performed to quantify phosphocreatine kinetics and pH, and for the remaining two visits (6 mg·kg^-1 caffeine vs placebo), femoral nerve electrical and transcranial magnetic stimulation of the quadriceps cortical motor area were applied pre- and post exercise.

Results

The total exercise time was 17.9 ± 6.0% longer in the caffeine (1,225 ± 86 s) than in the placebo trial (1,049 ± 73 s, p = 0.016), and muscle phosphocreatine concentration and pH (p < 0.05) were significantly lower in the latter sets of exercise after caffeine ingestion. Voluntary activation (VA) (peripheral, p = 0.007; but not supraspinal, p = 0.074), motor-evoked potential (MEP) amplitude (p = 0.007), and contractility (contraction time, p = 0.009; and relaxation rate, p = 0.003) were significantly higher after caffeine consumption, but at task failure MEP amplitude and VA were not different from placebo. Caffeine prevented the reduction in M-wave amplitude that occurred at task failure (p = 0.039).

Conclusion

Caffeine supplementation improved high-intensity exercise tolerance despite greater-end exercise knee extensor phosphocreatine depletion and H⁺ accumulation. Caffeine-induced increases in central motor drive and corticospinal excitability were attenuated at task failure. This may have been induced by the afferent feedback of the greater disturbance of the muscle milieu, resulting in a stronger inhibitory input to the spinal and supraspinal motor neurons. However, causality needs to be established through further experiments.

Caffeine and Bicarbonate for Speed. A Meta-Analysis of Legal Supplements Potential for Improving Intense Endurance Exercise Performance

A 1% change in average speed is enough to affect medal rankings in intense Olympic endurance events lasting ~45 s to 8 min which for example includes 100 m swimming and 400 m running (~1 min), 1,500 m running and 4000 m track cycling (~4 min) and 2,000 m rowing (~6-8 min). To maximize the likelihood of winning, athletes utilizes legal supplements with or without scientifically documented beneficial effects on performance. Therefore, a continued systematic evidence based evaluation of the possible ergogenic effects is of high importance. A meta-analysis was conducted with a strict focus on closed-end performance tests in humans in the time domain from 45 s to 8 min. These test include time-trials or total work done in a given time. This selection criterion results in a high relevance for athletic performance. Only peer-reviewed placebo controlled studies were included. The often applied and potentially ergogenic supplements beta-alanine, bicarbonate, caffeine and nitrate were selected for analysis. Following a systematic search in Pubmed and SportsDiscuss combined with evaluation of cross references a total of 7 (beta-alanine), 25 (bicarbonate), 9 (caffeine), and 5 (nitrate) studies was included in the meta-analysis. For each study, performance was converted to an average speed (km/h) from which an effect size (ES; Cohens d with 95% confidence intervals) was calculated. A small effect and significant performance improvement relative to placebo was observed for caffeine (ES: 0.41 [0.15–0.68], P = 0.002) and bicarbonate (ES: 0.40 [0.27–0.54], P < 0.001). Trivial and non-significant effects on performance was observed for nitrate (ES: 0.19 [−0.03–0.40], P = 0.09) and beta-alanine (ES: 0.17 [−0.12–0.46], P = 0.24). Thus, caffeine's and bicarbonate's ergogenic effect is clearly documented for intense endurance performance. Importantly, for all supplements an individualized approach may improve the ergogenic effect on performance.

Biochemical responses and physical performance during high-intensity resistance circuit training in hypoxia and normoxia

PURPOSE

The aim of this study was to analyze the effect of hypoxia on metabolic and acid-base balance, blood oxygenation, electrolyte, and half-squat performance variables during high-resistance circuit (HRC) training.

METHODS

Twelve resistance-trained subjects participated in this study. After a 6RM testing session, participants performed three randomized trials of HRC: normoxia (NORM: FiO₂ = 0.21), moderate hypoxia (MH: FiO₂ = 0.16), or high hypoxia (HH: FiO₂ = 0.13), separated by 72 h of recovery in normoxic conditions. HRC consisted of two blocks of three exercises (Block 1: bench press, deadlift and elbow flexion; Block 2: half-squat, triceps extension, and ankle extension). Each exercise was performed at 6RM. Rest periods lasted for 35 s between exercises, 3 min between sets, and 5 min between blocks. Peak and mean force and power were determined during half-squat. Metabolic, acid-base balance, blood oxygenation and electrolyte variables, arterial oxygen saturation (SaO₂), and rating of perceived exertion (RPE) were measured following each block.

RESULTS

During the first set, peak force and power were significantly lower in HH than MH and NORM; whereas in the second set, mean and peak force and power were significantly lower in HH than NORM. At the end of the HRC training session, blood lactate and RPE in HH were significantly higher than in MH and NORM. SaO₂, pH, HCO₃^-, and pO₂ values were significantly lower in all hypoxic conditions than in NORM.

CONCLUSION

These results indicate that simulated hypoxia during HRC exercise reduce blood oxygenation, pH, and HCO₃^-, and increased blood lactate ultimately decreasing muscular performance.

Conducted dilatation to ATP and K+ in rat skeletal muscle arterioles

AIM

During exercise in humans, circulating levels of ATP and K+ increase at a time when blood flow increases to satisfy metabolic demand. Both molecules can activate arteriolar K+ channels to stimulate vasodilatation; here, it is established whether conducted dilatation is observed in a skeletal muscle bed.

METHODS

Isolated and cannulated rat cremaster arterioles were used to assess both local and conducted responses. Agents were either added to the bath, focally pulse-ejected to the downstream end of arterioles, or in triple-cannulated arterioles, luminally perfused into the downstream branches to assess both local and conducted responses.

RESULTS

The endothelium-dependent agonist ACh and the KATP channel opener levcromakalim each stimulated both local and conducted vasodilatation. Focal, bolus delivery of ATP (10 μm) or KCl (33 mm) to the outside of arterioles stimulated a biphasic vasomotor response: rapid vasoconstriction followed by dilatation as each washed away. At lower concentrations of KCl (19 mm), constriction was avoided, and instead, Ba2+ -sensitive local dilatation and conducted dilatation were both observed. Luminal perfusion of ATP avoided constriction and activated P2Y1 receptors stimulating vasodilatation secondary to opening of KCa channels. In triple-cannulated arterioles, either ATP (10 μm) or K+ (15 mm) luminally perfused into daughter branches of a bifurcation stimulated local dilatation which conducted into the parent arteriole.

CONCLUSION

The recognized physiological autocrine and paracrine mediators ATP and K+ each act to evoke both local and conducted vasodilatation in rat cremaster arterioles. Therefore, in situations when circulating levels are raised, such as during exercise, these agents can act as important regulators of blood flow.

Limitations in intense exercise performance of athletes - effect of speed endurance training on ion handling and fatigue development

Mechanisms underlying fatigue development and limitations for performance during intense exercise have been intensively studied during the past couple of decades. Fatigue development may involve several interacting factors and depends on type of exercise undertaken and training level of the individual. Intense exercise (½-6 min) causes major ionic perturbations (Ca²⁺ , Cl^- , H⁺ , K⁺ , lactate^- and Na⁺ ) that may reduce sarcolemmal excitability, Ca²⁺ release and force production of skeletal muscle. Maintenance of ion homeostasis is thus essential to sustain force production and power output during intense exercise. Regular speed endurance training (SET), i.e. exercise performed at intensities above that corresponding to maximum oxygen consumption (V̇O2, max ), enhances intense exercise performance. However, most of the studies that have provided mechanistic insight into the beneficial effects of SET have been conducted in untrained and recreationally active individuals, making extrapolation towards athletes' performance difficult. Nevertheless, recent studies indicate that only a few weeks of SET enhances intense exercise performance in highly trained individuals. In these studies, the enhanced performance was not associated with changes in V̇O2, max and muscle oxidative capacity, but rather with adaptations in muscle ion handling, including lowered interstitial concentrations of K⁺ during and in recovery from intense exercise, improved lactate^- -H⁺ transport and H⁺ regulation, and enhanced Ca²⁺ release function. The purpose of this Topical Review is to provide an overview of the effect of SET and to discuss potential mechanisms underlying enhancements in performance induced by SET in already well-trained individuals with special emphasis on ion handling in skeletal muscle.

Mechanistic Insights into the Efficacy of Sodium Bicarbonate Supplementation to Improve Athletic Performance

A large proportion of empirical research and reviews investigating the ergogenic potential of sodium bicarbonate (NaHCO₃) supplementation have focused predominately on performance outcomes and only speculate about underlying mechanisms responsible for any benefit. The aim of this review was to critically evaluate the influence of NaHCO₃ supplementation on mechanisms associated with skeletal muscle fatigue as it translates directly to exercise performance. Mechanistic links between skeletal muscle fatigue, proton accumulation (or metabolic acidosis) and NaHCO₃ supplementation have been identified to provide a more targeted, evidence-based approach to direct future research, as well as provide practitioners with a contemporary perspective on the potential applications and limitations of this supplement. The mechanisms identified have been broadly categorised under the sections ‘Whole-body Metabolism’, ‘Muscle Physiology’ and ‘Motor Pathways’, and when possible, the performance outcomes of these studies contextualized within an integrative framework of whole-body exercise where other factors such as task demand (e.g. large vs. small muscle groups), cardio-pulmonary and neural control mechanisms may outweigh any localised influence of NaHCO₃. Finally, the ‘Performance Applications’ section provides further interpretation for the practitioner founded on the mechanistic evidence provided in this review and other relevant, applied NaHCO₃ performance-related studies.

The effect of metabolic alkalosis on central and peripheral mechanisms associated with exercise-induced muscle fatigue in humans

NEW FINDINGS

What is the central question of this study? Does metabolic alkalosis affect central and peripheral mechanisms associated with exercise-induced muscle fatigue in humans? What is the main finding and its importance? Inducing metabolic alkalosis before exercise preserved voluntary activation, but not muscle excitation, after a 2 min maximal voluntary contraction (MVC) followed by ischaemia. An effect of pH was also observed in maximal rates of torque development, where alkalosis mitigated the reduction in maximal rates of torque development after the initial 2 min MVC. For the first time, these results demonstrate a differential effect of pH on voluntary activation as well as maximal rates of torque development after sustained, maximal voluntary knee extension in humans. The increased concentration of protons during fatiguing exercise may contribute to increased activation of group III and IV afferents and subsequently reduced central drive, but this has yet to be confirmed in exercising humans. Here, we determined whether inducing metabolic alkalosis differentially affects descending central drive after fatiguing exercise and whether this effect may, in part, be explained by attenuating group III and IV afferent firing. Eleven men performed a maximal 2 min voluntary knee extension (MVC) followed by a 2 min rest and subsequent 1 min MVC with an occlusive cuff either in placebo [PLA; 0.3 g (kg body weight)(-1) calcium carbonate] or alkalosis conditions [ALK; 0.3 g (kg body weight)(-1) sodium bicarbonate]. Femoral nerve stimulation was applied before exercise, after the 2 min MVC and at 40-60 s intervals throughout the remainder of the protocol to explore central and peripheral mechanisms associated with reductions in maximal force and rate of torque development. Although voluntary activation declined to a similar extent after the 2 min MVC, during the ischaemic period voluntary activation was higher during ALK (PLA, 57 ± 8%; ALK, 76 ± 5%). Maximal voluntary torque declined at similar rates during the task (203 ± 19 N m), but maximal rate of torque development was significantly higher in the ALK conditions after the 2 min MVC (mean difference of 177 ± 60 N m s(-1) ). These results demonstrate the effect of pH on voluntary activation as well as maximal rates of torque development after sustained, maximal voluntary knee extension in humans.

Effects of traditional vs. alternating whole-body strength training on squat performance

Traditional strength training with 80% of 1 repetition maximum (1RM) uses 2- to 5-minute rest periods between sets. These long rest periods minimize decreases in volume and intensity but result in long workouts. Performing upper-body exercises during lower-body rest intervals may decrease workout duration but may affect workout performance. Therefore, the purpose of this study was to compare the effects of traditional vs. alternating whole-body strength training on squat performance. Twenty male (24 ± 2 years) volunteers performed 2 workouts. The traditional set (TS) workout consisted of 4 sets of squats (SQ) at 80% of 1RM on a force plate with 3-minute rest between sets. The alternating set (AS) workout also consisted of 4 sets of SQ at 80% of 1RM but with bench press, and bench pull exercises performed between squat sets 1, 2 and 3 with between-exercise rest of 50 seconds, resulting in approximately 3-minute rest between squat sets. Sets 1-3 were performed for 4 repetitions, whereas set 4 was performed to concentric failure. Total number of completed repetitions of the fourth squat set to failure was recorded. Peak ground reaction force (GRF), peak power (PP), and average power (AP) of every squat repetition were recorded and averaged for each set. There was no significant interaction for GRF, PP, or AP. However, volume-equated AP was greater during the TS condition (989 ± 183) than the AS condition (937 ± 176). During the fourth squat set, the TS condition resulted in more repetitions to failure (7.5 ± 2.2) than the AS condition (6.5 ± 2.2). Therefore, individuals who aim to optimize squat AP should refrain from performing more than 3 ASs per exercise. Likewise, those who aim to maximize squat repetitions to failure should refrain from performing upper-body multijoint exercises during squat rest intervals.

Effects of pre-exercise alkalosis on the decrease in VO2 at the end of all-out exercise

PURPOSE

This study determined the effects of pre-exercise sodium bicarbonate ingestion (ALK) on changes in oxygen uptake (VO2) at the end of a supramaximal exercise test (SXT).

METHODS

Eleven well-trained cyclists completed a 70-s all-out cycling effort, in double-blind trials, after oral ingestion of either 0.3 g kg(-1) of sodium bicarbonate (NaHCO3) or 0.2 g kg(-1) body mass of calcium carbonate (PLA). Blood samples were taken to assess changes in acid-base balance before the start of the supramaximal exercise, and 0, 5 and 8 min after the exercise; ventilatory parameters were also measured at rest and during the SXT.

RESULTS

At the end of the PLA trial, which induced mild acidosis (blood pH = 7.20), subjects presented a significant decrease in VO2 (P < 0.05), which was related to the amplitude of the decrease in minute ventilation (VE) during the SXT (r = 0.70, P < 0.01, n = 11). Pre-exercise metabolic alkalosis significantly prevented the exercise-induced decrease in VO2 in eleven well-trained participants (PLA:12.5 ± 2.1 % and ALK: 4.9 ± 0.9 %, P < 0.05) and the decrease in mean power output was significantly less pronounced in ALK (P < 0.05). Changes in the VO2 decrease between PLA and ALK trials were positively related to changes in the VE decrease (r = 0.74, P < 0.001), but not to changes in power output (P > 0.05).

CONCLUSIONS

Pre-exercise alkalosis counteracted the VO2 decrease related to mild acidosis, potentially as a result of changes in VE and in muscle acid-base status during the all-out supramaximal exercise.

Physiological and health-related adaptations to low-volume interval training: influences of nutrition and sex

Interval training refers to the basic concept of alternating periods of relatively intense exercise with periods of lower-intensity effort or complete rest for recovery. Low-volume interval training refers to sessions that involve a relatively small total amount of exercise (i.e. ≤10 min of intense exercise), compared with traditional moderate-intensity continuous training (MICT) protocols that are generally reflected in public health guidelines. In an effort to standardize terminology, a classification scheme was recently proposed in which the term 'high-intensity interval training' (HIIT) be used to describe protocols in which the training stimulus is 'near maximal' or the target intensity is between 80 and 100 % of maximal heart rate, and 'sprint interval training' (SIT) be used for protocols that involve 'all out' or 'supramaximal' efforts, in which target intensities correspond to workloads greater than what is required to elicit 100 % of maximal oxygen uptake (VO2max). Both low-volume SIT and HIIT constitute relatively time-efficient training strategies to rapidly enhance the capacity for aerobic energy metabolism and elicit physiological remodeling that resembles changes normally associated with high-volume MICT. Short-term SIT and HIIT protocols have also been shown to improve health-related indices, including cardiorespiratory fitness and markers of glycemic control in both healthy individuals and those at risk for, or afflicted by, cardiometabolic diseases. Recent evidence from a limited number of studies has highlighted potential sex-based differences in the adaptive response to SIT in particular. It has also been suggested that specific nutritional interventions, in particular those that can augment muscle buffering capacity, such as sodium bicarbonate, may enhance the adaptive response to low-volume interval training.

Sodium bicarbonate intake improves high-intensity intermittent exercise performance in trained young men

Background

Sodium bicarbonate intake has been shown to improve exercise tolerance, but the effects on high-intensity intermittent exercise are less clear. Thus, the aim of the present study was to determine the effect of sodium bicarbonate intake on Yo-Yo intermittent recovery test level 2 performance in trained young men.

Method

Thirteen men aged 23 ± 1 year (height: 180 ± 2 cm, weight: 78 ± 3 kg; VO₂max: 61.3 ± 3.3 mlO₂ · kg⁻¹ · min⁻¹; means ± SEM) performed the Yo-Yo intermittent recovery test level 2 (Yo-Yo IR2) on two separate occasions in randomized order with (SBC) and without (CON) prior intake of sodium bicarbonate (0.4 g · kg⁻¹ body weight). Heart rate and rating of perceived exertion (RPE) were measured during the test and venous blood samples were taken frequently.

Results

Yo-Yo IR2 performance was 14 % higher (P = 0.04) in SBC than in CON (735 ± 61 vs 646 ± 46 m, respectively). Blood pH and bicarbonate were similar between trials at baseline, but higher (P = 0.003) immediately prior to the Yo-Yo IR2 test in SBC than in CON (7.44 ± 0.01 vs 7.32 ± 0.01 and 33.7 ± 3.2 vs 27.3 ± 0.6 mmol · l⁻¹, respectively). Blood lactate was 0.9 ± 0.1 and 0.8 ± 0.1 mmol · l⁻¹ at baseline and increased to 11.3 ± 1.4 and 9.4 ± 0.8 mmol · l⁻¹ at exhaustion in SBC and CON, respectively, being higher (P = 0.03) in SBC. Additionally, peak blood lactate was higher (P = 0.02) in SBC than in CON (11.7 ± 1.2 vs 10.2 ± 0.7 mmol · l⁻¹). Blood glucose, plasma K⁺ and Na⁺ were not different between trials. Peak heart rate reached at exhaustion was 197 ± 3 and 195 ± 3 bpm in SBC and CON, respectively, with no difference between conditions. RPE was 7 % lower (P = 0.003) in SBC than in CON after 440 m, but similar at exhaustion (19.3 ± 0.2 and 19.5 ± 0.2).

Conclusion

In conclusion, high-intensity intermittent exercise performance is improved by prior intake of sodium bicarbonate in trained young men, with concomitant elevations in blood alkalosis and peak blood lactate levels, as well as lowered rating of perceived exertion.

Ergogenic effects of caffeine and sodium bicarbonate supplementation on intermittent exercise performance preceded by intense arm cranking exercise

BACKGROUND

Caffeine and sodium bicarbonate ingestion have been suggested to improve high-intensity intermittent exercise, but it is unclear if these ergogenic substances affect performance under provoked metabolic acidification. To study the effects of caffeine and sodium bicarbonate on intense intermittent exercise performance and metabolic markers under exercise-induced acidification, intense arm-cranking exercise was performed prior to intense intermittent running after intake of placebo, caffeine and sodium bicarbonate.

METHODS

Male team-sports athletes (n = 12) ingested sodium bicarbonate (NaHCO3; 0.4 g.kg(-1) b.w.), caffeine (CAF; 6 mg.kg(-1) b.w.) or placebo (PLA) on three different occasions. Thereafter, participants engaged in intense arm exercise prior to the Yo-Yo intermittent recovery test level-2 (Yo-Yo IR2). Heart rate, blood lactate and glucose as well as rating of perceived exertion (RPE) were determined during the protocol.

RESULTS

CAF and NaHCO3 elicited a 14 and 23% improvement (P < 0.05), respectively, in Yo-Yo IR2 performance, post arm exercise compared to PLA. The NaHCO3 trial displayed higher [blood lactate] (P < 0.05) compared to CAF and PLA (10.5 ± 1.9 vs. 8.8 ± 1.7 and 7.7 ± 2.0 mmol.L(-1), respectively) after the Yo-Yo IR2. At exhaustion CAF demonstrated higher (P < 0.05) [blood glucose] compared to PLA and NaHCO3 (5.5 ± 0.7 vs. 4.2 ± 0.9 vs. 4.1 ± 0.9 mmol.L(-1), respectively). RPE was lower (P < 0.05) during the Yo-Yo IR2 test in the NaHCO3 trial in comparison to CAF and PLA, while no difference in heart rate was observed between trials.

CONCLUSIONS

Caffeine and sodium bicarbonate administration improved Yo-Yo IR2 performance and lowered perceived exertion after intense arm cranking exercise, with greater overall effects of sodium bicarbonate intake.

The Neuro-Immune Pathophysiology of Central and Peripheral Fatigue in Systemic Immune-Inflammatory and Neuro-Immune Diseases

Many patients with systemic immune-inflammatory and neuro-inflammatory disorders, including depression, rheumatoid arthritis, systemic lupus erythematosus, Sjögren's disease, cancer, cardiovascular disorder, Parkinson's disease, multiple sclerosis, stroke, and chronic fatigue syndrome/myalgic encephalomyelitis, endure pathological levels of fatigue. The aim of this narrative review is to delineate the wide array of pathways that may underpin the incapacitating fatigue occurring in systemic and neuro-inflammatory disorders. A wide array of immune, inflammatory, oxidative and nitrosative stress (O&NS), bioenergetic, and neurophysiological abnormalities are involved in the etiopathology of these disease states and may underpin the incapacitating fatigue that accompanies these disorders. This range of abnormalities comprises: increased levels of pro-inflammatory cytokines, e.g., interleukin-1 (IL-1), IL-6, tumor necrosis factor (TNF) α and interferon (IFN) α; O&NS-induced muscle fatigue; activation of the Toll-Like Receptor Cycle through pathogen-associated (PAMPs) and damage-associated (DAMPs) molecular patterns, including heat shock proteins; altered glutaminergic and dopaminergic neurotransmission; mitochondrial dysfunctions; and O&NS-induced defects in the sodium-potassium pump. Fatigue is also associated with altered activities in specific brain regions and muscle pathology, such as reductions in maximum voluntary muscle force, downregulation of the mitochondrial biogenesis master gene peroxisome proliferator-activated receptor gamma coactivator 1-alpha, a shift to glycolysis and buildup of toxic metabolites within myocytes. As such, both mental and physical fatigue, which frequently accompany immune-inflammatory and neuro-inflammatory disorders, are the consequence of interactions between multiple systemic and central pathways.

Determination of micro and macro elements in iron supplements used for treatment of anemia and evaluation employing chemometric analysis tools

This paper propose a method using inductively coupled plasma optical emission spectrometry for the determination of micro and macro elements in pharmaceutical formulations used for anemia treatment and evaluation by chemometrics analysis tools.

Impact of acute sodium citrate ingestion on endurance running performance in a warm environment

PURPOSE

Dietary supplements inducing alkalosis have been shown to be ergogenic during intense endurance exercise in temperate environments, but there is lack of data regarding the efficacy of these substances in the heat. This study aimed to investigate the effect of sodium citrate (CIT) ingestion on 5,000-m running performance in a warm environment.

METHODS

Sixteen non-heat-acclimated endurance-trained males (age 25.8 ± 4.4 years, VO2peak 56.9 ± 4.7 mL kg min) completed two 5,000-m self-paced treadmill runs with preceding CIT or placebo (wheat flour; PLC) ingestion in a double-blind, randomized, crossover manner in a climatic chamber (air temperature 32 °C, relative humidity 50 %).

RESULTS

CIT ingestion (500 mg kg(-1) body mass) compared to PLC induced increases in water retention, body mass and plasma volume (P < 0.05). Pre- and post-exercise blood HCO3 (-) concentration, base excess and pH were higher (P < 0.001) in CIT compared to PLC trial. Rectal temperature, body heat storage, heat storage rate, heart rate and 5,000-m running time (18.92 ± 2.05 min in CIT, 19.11 ± 2.38 min in PLC; 66 % likelihood of benefit, d = -0.09) were similar (P > 0.05) in the two trials. Post-exercise blood lactate concentration was higher (P < 0.001) in CIT (11.05 ± 3.22 mmol L(-1)) compared to PLC trial (8.22 ± 2.64 mmol L(-1)). Ratings of perceived exertion, fatigue and thermal sensation did not differ in the two trials (P > 0.05).

CONCLUSION

Acute CIT ingestion induces alkalosis, water retention, plasma volume expansion and an increase in post-exercise blood lactate concentration, but does not improve 5,000-m running performance in a warm environment in non-heat-acclimated endurance-trained males.

Warm-up strategy and high-intensity endurance performance in trained cyclists

PURPOSE

To evaluate the influence of warm-up exercise intensity and subsequent recovery on intense endurance performance, selected blood variables, and the oxygen-uptake (VO2) response.

METHODS

Twelve highly trained male cyclists (VO2max 72.4 ± 8.0 mL · min-1 · kg-1, incremental-test peak power output (iPPO) 432 ± 31 W; mean ± SD) performed 3 warm-up strategies lasting 20 min before a 4-min maximal-performance test (PT). Strategies consisted of moderate-intensity exercise (50%iPPO) followed by 6 min of recovery (MOD6) or progressive high-intensity exercise (10-100%iPPO and 2 × 20-s sprints) followed by recovery for 6 min (HI6) or 20 min (HI20).

RESULTS

Before PT venous pH was lower (P < .001) in HI6 (7.27 ± 0.05) than in HI20 (7.34 ± 0.04) and MOD6 (7.35 ± 0.03). At the same time, differences (P < .001) existed for venous lactate in HI6 (8.2 ± 2.0 mmol/L), HI20 (5.1 ± 1.7 mmol/L), and MOD6 (1.4 ± 0.4 mmol/L), as well as for venous bicarbonate in HI6 (19.3 ± 2.6 mmol/L), HI20 (22.6 ± 2.3 mmol/L), and MOD6 (26.0 ± 1.4 mmol/L). Mean power in PT in HI6 (402 ± 38 W) tended to be lower (P = .11) than in HI20 (409 ± 34 W) and was lower (P = .007) than in MOD6 (416 ± 32 W). Total VO2 (15-120 s in PT) was higher in HI6 (8.18 ± 0.86 L) than in HI20 (7.85 ± 0.82 L, P = .008) and MOD6 (7.90 ± 0.74 L, P = .012).

CONCLUSIONS

Warm-up exercise including race-pace and sprint intervals combined with short recovery can reduce subsequent performance in a 4-min maximal test in highly trained cyclists. Thus, a reduced time at high exercise intensity, a reduced intensity in the warm-up, or an extension of the recovery period after an intense warm-up is advocated.