Metabolic effects of induced alkalosis during progressive forearm exercise to fatigue

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.

Plasma Acidosis and Peak Power after a Supramaximal Trial in Elite Sprint and Endurance Cyclists: Effect of Bicarbonate

PURPOSE

This study aimed to determine whether (i) a plasma acidosis contributes to a reduction of mechanical performance and (ii) bicarbonate supplementation blunts plasma acidosis and arterial oxygen desaturation to resist fatigue during the end spurt of a supramaximal trial in elite sprint and endurance cyclists.

METHODS

Elite/world-class cyclists ( n = 6 sprint, n = 6 endurance) completed two randomized, double-blind, crossover trials at 105%V̇O 2peak simulating 3 min of a 4-km individual pursuit, 90 min after ingestion of 0.3 g·kg -1 BM sodium bicarbonate (BIC) or placebo (PLA). Peak power output (PPO), optimal cadence and optimal peak torque, and fatigue were assessed using a 6-s "all-out sprint" before (PPO1) and after (PPO2) each trial. Plasma pH, bicarbonate, lactate - , K + , Na + , Ca 2+ , and arterial hemoglobin saturation (SpO 2 (%)), were measured.

RESULTS

Sprint cyclists exhibited a higher PPO, optimal pedal torque, and anaerobic power reserve (APR) than endurance cyclists. The trial reduced PPO (PLA) more for sprint (to 47% initial) than endurance cyclists (to 61% initial). Optimal cadence fell from ~151 to 92 rpm and cyclists with higher APR exhibited a reduced optimal peak torque. Plasma pH fell from 7.35 to 7.13 and plasma [lactate - ] increased from 1.2 to 19.6 mM (PLA), yet neither correlated with PPO loss. Sprint cyclists displayed a lesser plasma acidosis but greater fatigue than endurance cyclists. BIC increased plasma [HCO 3- ] (+6.8 mM) and plasma pH after PPO1 (+0.09) and PPO2 (+0.07) yet failed to influence mechanical performance. SpO 2 fell from 99% to 96% but was unrelated to the plasma acidosis and unaltered with BIC.

CONCLUSIONS

Plasma acidosis was not associated with the decline of PPO in a supramaximal trial with elite cyclists. BIC attenuated acid-base disturbances yet did not improve arterial oxygen desaturation or mechanical performance at the end-spurt stage.

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.

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.

Effects of Prior Voluntary Hyperventilation on the 3-min All-Out Cycling Test in Men

INTRODUCTION

The ergogenic effects of respiratory alkalosis induced by prior voluntary hyperventilation (VH) are controversial. This study examined the effects of prior VH on derived parameters from the 3-min all-out cycling test (3MT).

METHODS

Eleven men ( = 46 ± 8 mL·kg-1·min-1) performed a 3MT preceded by 15 min of rest (CONT) or VH ( = 38 ± 5 L·min-1) with PETCO2 reduced to 21 ± 1 mm Hg (HYP). End-test power (EP; synonymous with critical power) was calculated as the mean power output over the last 30 s of the 3MT, and the work done above EP (WEP; synonymous with W') was calculated as the power-time integral above EP.

RESULTS

At the start of the 3MT, capillary blood PCO2 and [H+] were lower in HYP (25.2 ± 3.0 mm Hg, 27.1 ± 2.6 nmol·L-1) than CONT (43.2 ± 2.0 mm Hg, 40.0 ± 1.5 nmol·L-1) (P < 0.001). At the end of the 3MT, blood PCO2 was still lower in HYP (35.7 ± 5.4 mm Hg) than CONT (40.6 ± 5.0 mm Hg) (P < 0.001). WEP was 10% higher in HYP (19.4 ± 7.0 kJ) than CONT (17.6 ± 6.4 kJ) (P = 0.006), whereas EP was 5% lower in HYP (246 ± 69 W) than CONT (260 ± 74 W) (P = 0.007). The ΔWEP (J·kg-1) between CONT and HYP correlated positively with the PCO2 immediately before the 3MT in HYP (r = 0.77, P = 0.006).

CONCLUSION

These findings suggest that acid-base changes elicited by prior VH increase WEP but decrease EP during the all-out 3MT.

Effects of a nutraceutical supplement on gastrointestinal health in racing standardbreds

BACKGROUND

Feed additives that accelerate gastrointestinal transit time may help support normal gastrointestinal function in horses at risk for impaction colic. Previous research has demonstrated significant stimulatory effect of a hemp-based nutraceutical product (Gs Formula; GF) on contractility of gastric smooth muscle and gastrin production in vitro.

OBJECTIVES

To quantify effects of GF on indicators of GIT transit time and tight junction proteins.

STUDY DESIGN

Randomized placebo-controlled cross-over study.

METHODS

Eight Standardbreds were administered 200 plastic beads by nasogastric tube before (baseline; BL) and after receiving a diet containing GF (CON: 0 g/day, LO: 160 g/day or HI: 480 g/day) for 28 days. Total manure collection occurred every 2 hours for 72 hours after bead administration. Outcome measures included GIT transit time, faecal dry matter (DM), water intake, and complete biochemistry and haematology screens.

RESULTS

There was no effect of GF on GIT transit time. Faecal output was significantly lower in LO and HI horses than CON horses after 28 days on the supplement. HI horses have significantly lower rouleaux formation and lower faecal DM on Day 28 compared with BL. GF also produced changes in electrolytes associated with pH balance, which may indicate a role for GF as an alkalinizing compound in exercising horses. Clinical pathology results support the safety of GF up to 480 g/day for 28 days with no adverse effects being observed in haematology or biochemistry results.

MAIN LIMITATIONS

Future studies on GF should focus on evaluating effect of GF on gastrointestinal transit in horses with naturally or experimentally delayed gastrointestinal motility, and its effect on exercise performance and onset of fatigue.

CONCLUSIONS

GF may help support normal gastrointestinal function in horses at risk for impaction colic by reducing faecal DM and rouleaux formation.

Assessment of acute neuromuscular fatigue manifestations and functional performances after heavy resistance exercise

BACKGROUND

This study aimed to assess neuromuscular fatigue after heavy resistance exercise in rugby players.

METHODS

Twelve male rugby players performed five sets of knee extension exercise lifting 80% of their one repetition maximum until failure, with 3min of rest in-between. Maximal voluntary contraction (MVC) and surface electromyographic activity from quadriceps muscles, as well as ions (i.e., Na+, K+, and Cl-) and metabolic responses (i.e., blood lactate and ammonia concentrations) were measured before and after exercise. Maximum repetitions performance and both peripheral (RPEp) and overall body (RPEo) rating of perceived exertion were recorded following each set.

RESULTS

The number of maximum repetitions decreased significantly across sets (P<0.001). Both RPEp and RPEo increased significantly across sets (P<0.001) with higher RPEp values after each set (P<0.001). Both RPEp (r=-0.98, P<0.01) and RPEo (r=-0.99, P<0.001) were negatively correlated with the changes in the number of maximum repetitions. MVC (P<0.001), root mean square (P<0.05), and neuromuscular efficiency (P<0.01) as well as Na+ (P<0.01), Cl- (P<0.001) and blood concentrations of lactate (P<0.001) and ammonia (P<0.001) decreased significantly after the exercise. However, K+ (P<0.001) increased after the resistance exercise.

CONCLUSIONS

Heavy resistance exercise affected both objective (i.e., neuromuscular and biochemical parameters) and subjective (i.e., RPE) aspects of neuromuscular fatigue.

Enteric-coated sodium bicarbonate supplementation improves high-intensity cycling performance in trained cyclists

Purpose

Enteric-coated sodium bicarbonate (NaHCO₃) can attenuate gastrointestinal (GI) symptoms following acute bicarbonate loading, although the subsequent effects on exercise performance have not been investigated. The purpose of this study was to examine the effects of enteric-coated NaHCO₃ supplementation on high-intensity exercise performance and GI symptoms.

Methods

Eleven trained male cyclists completed three 4 km time trials after consuming; a placebo or 0.3 g∙kg^–1 body mass NaHCO₃ in enteric-coated or gelatin capsules. Exercise trials were timed with individual peak blood bicarbonate ion concentration ([HCO₃^–]). Blood acid–base balance was measured pre-ingestion, pre-exercise, and post-exercise, whereas GI symptoms were recorded pre-ingestion and immediately pre-exercise.

Results

Pre-exercise blood [HCO3⁻] and potential hydrogen (pH) were greater for both NaHCO₃ conditions (P < 0.0005) when compared to placebo. Performance time was faster with enteric-coated (− 8.5 ± 9.6 s, P = 0.044) and gelatin (− 9.6 ± 7.2 s, P = 0.004) NaHCO₃ compared to placebo, with no significant difference between conditions (mean difference = 1.1 ± 5.3 s, P = 1.000). Physiological responses were similar between conditions, although blood lactate ion concentration was higher with gelatin NaHCO₃ (2.4 ± 1.7 mmol∙L^–1, P = 0.003) compared with placebo. Furthermore, fewer participants experienced GI symptoms with enteric-coated (n = 3) compared to gelatin (n = 7) NaHCO₃.

Discussion

Acute enteric-coated NaHCO₃ consumption mitigates GI symptoms at the onset of exercise and improves subsequent 4 km cycling TT performance. Athletes who experience GI side-effects after acute bicarbonate loading may, therefore, benefit from enteric-coated NaHCO₃ supplementation prior to exercise performance.

Impact of sodium citrate ingestion during recovery after dehydrating exercise on rehydration and subsequent 40-km cycling time-trial performance in the heat

The purpose of this study was to assess the impact of sodium citrate (CIT) ingestion (600 mg·kg^-1) during recovery from dehydrating cycling exercise (DE) on subsequent 40-km cycling performance in a warm environment (32 °C). Twenty male nonheat-acclimated endurance athletes exercised in the heat until 4% body mass (BM) loss occurred. After 16 h recovery with consumption of water ad libitum and prescribed diet (evening meal 20 kcal·kg^-1, breakfast 12 kcal·kg^-1) supplemented in a double-blind, randomized, crossover manner with CIT or placebo (PLC), they performed 40-km time-trial (TT) on a cycle ergometer in a warm environment. During recovery greater increases in BM and plasma volume (PV) concomitant with greater water intake and retention occurred in the CIT trial compared with the PLC trial (p < 0.0001). During TT there was greater water intake and smaller BM loss in the CIT trial than in the PLC trial (p < 0.05) with no between-trial differences (p > 0.05) in sweat loss, PV decrement, ratings of perceived exertion, or TT time (CIT 68.10 ± 3.28 min, PLC 68.11 ± 2.87 min). At the end of TT blood lactate concentration was higher (7.58 ± 2.44 mmol·L^-1 vs 5.58 ± 1.32 mmol·L^-1; p = 0.0002) and rectal temperature lower (39.54 ± 0.50 °C vs 39.65 ± 0.52 °C; p = 0.033) in the CIT trial than in the PLC trial. Compared with pre-DE time point, PV had decreased to a lower level in the PLC trial than in the CIT trial (p = 0.0001). In conclusion, CIT enhances rehydration after exercise-induced dehydration but has no impact on subsequent 40-km cycling TT performance in a warm uncompensable environment.

The influence of sodium bicarbonate on maximal force and rates of force development in the triceps surae and brachii during fatiguing exercise

NEW FINDINGS

What is the central question of this study? Does metabolic alkalosis in humans, induced by sodium bicarbonate, affect rates of skeletal muscle fatigue differentially in muscle groups composed predominately of slow- and fast-twitch fibres? What is the main finding and its importance? Sodium bicarbonate exhibited no effect on the fatigue profile observed between triceps surae and brachii muscle groups during and after 2 min of tetanic stimulation. For the first time in exercising humans, we have profiled the effect of sodium bicarbonate on the voluntary and involuntary contractile characteristics of muscle groups representative of predominately slow- and fast-twitch fibres. The effect of metabolic alkalosis on fibre-specific maximal force production and rates of force development (RFD) has been investigated previously in animal models, with evidence suggesting an improved capacity to develop force rapidly in fast- compared with slow-twitch muscle. We have attempted to model in vivo the fatigue profile of voluntary and involuntary maximal force and RFD in the triceps surae and brachii after sodium bicarbonate (NaHCO₃ ) ingestion. In a double-blind, three-way repeated-measures design, participants (n = 10) ingested either 0.3 g kg^-1 NaHCO₃ (ALK) or equivalent calcium carbonate (PLA) prior to 2 min of continuous (1 Hz) supramaximal stimulation (300 ms at 40 Hz) of the triceps surae or brachii, with maximal voluntary efforts (maximal voluntary torque) coupled with direct muscle stimulation also measured at baseline, 1 and 2 min. Metabolic alkalosis was achieved in both ALK trials but was not different between muscle groups. Regardless of the conditions, involuntary torque declined nearly 60% in the triceps brachii (P < 0.001) and ∼30% in the triceps surae (P < 0.001). In all trials, there was a significant decline in normalized involuntary RFD (P < 0.05). Maximal voluntary torque declined nearly 28% but was not different between conditions (P < 0.01), and although declining nearly 21% in voluntary RFD (P < 0.05) there was no difference between PLA and ALK in either muscle group (P = 0.93). Sodium bicarbonate exhibited no effect on the fatigue observed between representative fibre-type muscle groups on maximal voluntary and involuntary torque or rates of torque development during and after 2 min of tetanic stimulation.

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.

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.

Simple and effective exercise design for assessing in vivo mitochondrial function in clinical applications using (31)P magnetic resonance spectroscopy

The growing recognition of diseases associated with dysfunction of mitochondria poses an urgent need for simple measures of mitochondrial function. Assessment of the kinetics of replenishment of the phosphocreatine pool after exercise using (31)P magnetic resonance spectroscopy can provide an in vivo measure of mitochondrial function; however, the wider application of this technique appears limited by complex or expensive MR-compatible exercise equipment and protocols not easily tolerated by frail participants or those with reduced mental capacity. Here we describe a novel in-scanner exercise method which is patient-focused, inexpensive, remarkably simple and highly portable. The device exploits an MR-compatible high-density material (BaSO4) to form a weight which is attached directly to the ankle, and a one-minute dynamic knee extension protocol produced highly reproducible measurements of post-exercise PCr recovery kinetics in both healthy subjects and patients. As sophisticated exercise equipment is unnecessary for this measurement, our extremely simple design provides an effective and easy-to-implement apparatus that is readily translatable across sites. Its design, being tailored to the needs of the patient, makes it particularly well suited to clinical applications, and we argue the potential of this method for investigating in vivo mitochondrial function in new cohorts of growing clinical interest.

Sodium bicarbonate supplementation improved MAOD but is not correlated with 200- and 400-m running performances: a double-blind, crossover, and placebo-controlled study

The aim of the study was to investigate the effects of acute supplementation of sodium bicarbonate (NaHCO3) on maximal accumulated oxygen deficit (MAOD) determined by a single supramaximal effort (MAODALT) in running and the correlation with 200- and 400-m running performances. Fifteen healthy men (age, 23 ± 4 years; maximal oxygen uptake, 50.6 ± 6.1 mL·kg−1·min−1) underwent a maximal incremental exercise test and 2 supramaximal efforts at 110% of the intensity associated with maximal oxygen uptake, which was carried out after ingesting either 0.3 g·kg−1 body weight NaHCO3 or a placebo (dextrose) and completing 200- and 400-m performance tests. The study design was double-blind, crossover, and placebo-controlled. Significant differences were found between the NaHCO3 and placebo conditions for MAODALT (p = 0.01) and the qualitative inference for substantial changes showed a very likely positive effect (98%). The lactic anaerobic contribution in the NaHCO3 ingestion condition was significantly higher (p < 0.01) and showed a very likely positive effect (99% chance), similar to that verified for peak blood lactate concentration (p < 0.01). No difference was found for time until exhaustion (p = 0.19) or alactic anaerobic contribution (p = 0.81). No significant correlations were observed between MAODALT and 200- and 400-m running performance tests. Therefore, we can conclude that both MAODALT and the anaerobic lactic metabolism are modified after acute NaHCO3 ingestion, but it is not correlated with running performance.

Muscle fatigue resistance in the rat hindlimbin vivofrom low dietary intakes of tuna fish oil that selectively increase phospholipidn-3 docosahexaenoic acid according to muscle fibre type

Dietary fish oil (FO) modulates muscle O2consumption and contractile function, predictive of effects on muscle fatigue. High doses unattainable through human diet and muscle stimulation parameters used engender uncertainty in their physiological relevance. We tested the hypothesis that nutritionally relevant FO doses can modulate membrane fatty acid composition and muscle fatigue. Male Sprague–Dawley rats were randomised to control (10 % olive oil (OO) by weight) or low or moderate FO diet (LowFO and ModFO) (HiDHA tuna fish oil) for 15 weeks (LowFO: 0·3 % FO, 9·7 % OO, 0·25 % energy as EPA+DHA; ModFO: 1·25 % FO, 8·75 % OO, 1·0 % energy as EPA+DHA). Hindlimb muscle function was assessed under anaesthesiain vivousing repetitive 5 s burst sciatic nerve stimulation (0·05 ms, 7–12 V, 5 Hz, 10 s duty cycle, 300 s). There were no dietary differences in maximum developed muscle force. Repetitive peak developed force fell to 50 % within 62 (sem10) s in controls and took longer to decline in FO-fed rats (LowFO 110 (sem15) s; ModFO 117 (sem14) s) (P<0·05). Force within bursts was better sustained with FO and maximum rates of force development and relaxation declined more slowly. The FO-fed rats incorporated higher muscle phospholipid DHA-relative percentages than controls (P<0·001). Incorporation of DHA was greater in the fast-twitch gastrocnemius (Control 9·3 (sem0·8) %, LowFO 19·9 (sem0·4), ModFO 24·3 (sem1·0)) than in the slow-twitch soleus muscle (Control 5·1 (sem0·2), LowFO 14·3 (sem0·7), ModFO 18·0 (sem1·4)) (P<0·001), which was comparable with the myocardium, in line with muscle fibre characteristics. The LowFO and ModFO diets, emulating human dietary and therapeutic supplement intake, respectively, both elicited muscle membrane DHA enrichment and fatigue resistance, providing a foundation for translating these physiological effects to humans.

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.

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.

Dietary sodium citrate supplementation does not improve upper-body anaerobic performance in trained wrestlers in simulated competition-day conditions

PURPOSE

Similarly to a wrestling match, upper-body intermittent sprint performance (UBISP) test elicits severe acidosis. This study aimed to determine whether sodium citrate (CIT) ingestion would help to better maintain peak power (PP) and mean power (MP) output across four consecutive UBISP tests simulating wrestling matches of a competition-day.

METHODS

In a double-blind, counterbalanced, crossover manner, 11 trained wrestlers ingested either placebo (PLC) or CIT (900 mg kg(-1)) within a 17-h supplementation period. Thereafter they completed four (T1-T4) 6-min UBISP tests interspersed with 30-min recovery periods.

RESULTS

Compared with PLC, CIT supplementation resulted in a persistent increase (P < 0.05) in blood HCO3 (-) concentration and pH: pre-T1 25.6 % and 0.08 units, post-T4 39.1 % and 0.14 units, respectively. Post-T1 blood lactate concentration in CIT (16.1 ± 3.8 mmol L(-1)) was higher (P = 0.037) than that in PLC (13.7 ± 2.3 mmol L(-1)). Decrease in plasma volume across the supplementation period and UBISP tests was greater (P = 0.03) in PLC (-6.91 ± 4.37 %) than in CIT (-1.51 ± 4.34 %). There was an overall decrease (P = 0.028) in ratings of perceived exertion in CIT compared with PLC, but no between-trial difference (P > 0.05) in PP or MP in any UBISP test occurred.

CONCLUSION

In trained wrestlers, CIT ingestion induces alkalosis, counteracts reduction in plasma volume, increases post-test blood lactate concentration and reduces perceived exertion, but does not improve PP or MP attained in consecutive UBISP tests simulating four wrestling matches of a competition-day.

Caffeine, but not bicarbonate, improves 6 min maximal performance in elite rowers

This study examined the ergogenic effects in a 6 min maximal performance test (PT) on 12 elite rowers: 6 open-weight (mean ± SD; 25 ± 1 years, and 92 ± 3 kg) and 6 light-weight (25 ± 3 years, and 73 ± 6 kg), following supplementation with caffeine (CAF), sodium bicarbonate (SB), and the combination of both, in a double-blind randomized placebo (PLA) controlled design. PT was executed on 4 occasions, on separate days within a week, and in a non-fasted state, with standardized training being performed the day before PT. Protocols were as follows: (i) CAF, 3 mg/kg, 45 min prior to PT + calcium as SB-PLA; (ii) SB, 0.3 g/kg, 75 min prior to PT + dextrose as CAF-PLA; (iii) CAF + SB; and (iv) PLA; CAF-PLA + SB-PLA. The total distance in the CAF (1878 ± 97 m) and CAF + SB (1877 ± 97 m) was longer than in the PLA (1865 ± 104 m; P < 0.05) and SB (1860 ± 96 m; P < 0.01). The mean power in CAF (400 ± 58 W) and CAF + SB (400 ± 58 W) was higher than the PLA (393 ± 61 W; P < 0.05) and SB (389 ± 57 W; P < 0.01). In CAF and CAF + SB, power was higher (P < 0.05) relative to PLA in the last half (4-6 min) of PT. Trials with CAF were more effective in light-weight rowers (1.0% ± 0.8% improvement in distance; P < 0.05) than in open-weight rowers (0.3% ± 0.8%; P > 0.05). No difference between interventions was observed for readiness and stomach comfort before PT and perceived exertion during PT. This study demonstrates that caffeine ingestion does improve performance in elite rowing. In contrast sodium bicarbonate does not appear to be ergogenic, but it does not abolish the ergogenic effect of caffeine.

The differential effect of metabolic alkalosis on maximum force and rate of force development during repeated, high-intensity cycling

The purpose of this investigation was to assess the influence of sodium bicarbonate supplementation on maximal force production, rate of force development (RFD), and muscle recruitment during repeated bouts of high-intensity cycling. Ten male and female ( n = 10) subjects completed two fixed-cadence, high-intensity cycling trials. Each trial consisted of a series of 30-s efforts at 120% peak power output (maximum graded test) that were interspersed with 30-s recovery periods until task failure. Prior to each trial, subjects consumed 0.3 g/kg sodium bicarbonate (ALK) or placebo (PLA). Maximal voluntary contractions were performed immediately after each 30-s effort. Maximal force (Fmax) was calculated as the greatest force recorded over a 25-ms period throughout the entire contraction duration while maximal RFD (RFDmax) was calculated as the greatest 10-ms average slope throughout that same contraction. Fmax declined similarly in both the ALK and PLA conditions, with baseline values (ALK: 1,226 ± 393 N; PLA: 1,222 ± 369 N) declining nearly 295 ± 54 N [95% confidence interval (CI) = 84–508 N; P < 0.006]. RFDmax also declined in both trials; however, a differential effect persisted between the ALK and PLA conditions. A main effect of condition was observed across the performance time period, with RFDmax on average higher during ALK (ALK: 8,729 ± 1,169 N/s; PLA: 7,691 ± 1,526 N/s; mean difference between conditions 1,038 ± 451 N/s, 95% CI = 17–2,059 N/s; P < 0.048). These results demonstrate a differential effect of alkalosis on maximum force vs. maximum rate of force development during a whole body fatiguing task.

Sodium bicarbonate supplementation improves hypertrophy-type resistance exercise performance

The aim of the present study was to examine the effects of sodium bicarbonate (NaHCO(3)) administration on lower-body, hypertrophy-type resistance exercise (HRE). Using a double-blind randomized counterbalanced design, 12 resistance-trained male participants (mean ± SD; age = 20.3 ± 2 years, mass = 88.3 ± 13.2 kg, height = 1.80 ± 0.07 m) ingested 0.3 g kg(-1) of NaHCO(3) or placebo 60 min before initiation of an HRE regimen. The protocol employed multiple exercises: squat, leg press, and knee extension, utilizing four sets each, with 10-12 repetition-maximum loads and short rest periods between sets. Exercise performance was determined by total repetitions generated during each exercise, total accumulated repetitions, and a performance test involving a fifth set of knee extensions to failure. Arterialized capillary blood was collected via fingertip puncture at four time points and analyzed for pH, [HCO(3)(-)], base excess (BE), and lactate [Lac(-)]. NaHCO(3) supplementation induced a significant alkaline state (pH: NaHCO(3): 7.49 ± 0.02, placebo: 7.42 ± 0.02, P < 0.05; [HCO(3)(-)]: NaHCO(3): 31.50 ± 2.59, placebo: 25.38 ± 1.78 mEq L(-1), P < 0.05; BE: NaHCO(3): 7.92 ± 2.57, placebo: 1.08 ± 2.11 mEq L(-1), P < 0.05). NaHCO(3) administration resulted in significantly more total repetitions than placebo (NaHCO(3): 139.8 ± 13.2, placebo: 134.4 ± 13.5), as well as significantly greater blood [Lac(-)] after the exercise protocol (NaHCO(3): 17.92 ± 2.08, placebo: 15.55 ± 2.50 mM, P < 0.05). These findings demonstrate ergogenic efficacy for NaHCO(3) during HRE and warrant further investigation into chronic training applications.

Influence of an alkalizing supplement on markers of endurance performance using a double-blind placebo-controlled design

Background

Previous research has shown that ingestion of substances that enhance the body's hydrogen ion buffering capacity during high intensity exercise can improve exercise performance. The present study aimed to determine whether the chronic ingestion of an alkalizing supplement, which purports to enhance both intracellular and extracellular buffering capacity, could impact cardiorespiratory and performance markers in trained Nordic skiers.

Methods

Twenty-four skiers (12 men, 12 women), matched for upper body power (UBP), were split into treatment and placebo groups. The treatment group ingested Alka-Myte^®-based alkalizing tablets (1 tablet/22.7 kg body mass/day) over seven successive days while the placebo group consumed placebo tablets (i.e., no Alka-Myte^®) at the same dosage. Prior to tablet ingestion (i.e., pre-testing), both groups completed a constant power UBP test, three successive 10-sec UBP tests, and then a 60-sec UBP test. Next, skiers completed the 7-day ingestion of their assigned tablets followed immediately by a repeat of the same UBP tests (i.e., post-testing). Neither the skiers nor the researchers were aware of which tablets were being consumed by either group until after all testing was complete. Dependent measures for analysis included heart rate (HR), oxygen consumption (VO₂), minute ventilation (V_E), blood lactate (LA), as well as 10-sec (W10, W) and 60-sec (W60, W) UBP. All data were evaluated using a two-factor multivariate repeated measures ANOVA with planned contrasts for post-hoc testing (alpha = 0.05).

Results

Post-testing cardiorespiratory (HR, VO₂, V_E) and LA measures for the treatment group tended to be significantly lower when measured for both constant power and UBP60 tests, while measures of both 10-sec (W10: 229 to 243 W) and 60-sec UBP (W60: 190 to 198 W) were significantly higher (P < 0.05). In contrast, there were no significant changes for the placebo group (P > 0.05).

Conclusions

Following the 7-day loading phase of Alka-Myte^®-based alkalizing tablets, trained Nordic skiers experienced significantly lower cardiorespiratory stress, lower blood lactate responses, and higher UBP measures. Thus, the use of this supplement appeared to impart an ergogenic benefit to the skiers that may be similar to the effects expected from consuming well-studied extracellular buffering agents such as sodium bicarbonate.

Sodium bicarbonate ingestion and repeated swim sprint performance

The purpose of the present investigation was to observe the ergogenic potential of 0.3 g·kg-1 of sodium bicarbonate (NaHCO3) in competitive, nonelite swimmers using a repeated swim sprint design that eliminated the technical component of turning. Six male (181.2 ± 7.2 cm; 80.3 ± 11.9 kg; 50.8 ± 5.5 ml·kg-1·min-1 VO2max) and 8 female (168.8 ± 5.6 cm; 75.3 ± 10.1 kg; 38.8 ± 2.6 ml·kg-1·min-1 VO2max) swimmers completed 2 trial conditions (NaHCO3 [BICARB] and NaCl placebo [PLAC]) implemented in a randomized (counterbalanced), single blind manner, each separated by 1 week. Swimmers were paired according to ability and completed 8, 25-m front crawl maximal effort sprints each separated by 5 seconds. Blood acid-base status was assessed preingestion, pre, and postswim via capillary finger sticks, and total swim time was calculated as a performance measure. Total swim time was significantly decreased in the BICARB compared to PLAC condition (p = 0.04), with the BICARB condition resulting in a 2% decrease in total swim time compared to the PLAC condition (159.4 ± 25.4 vs. 163.2 ± 25.6 seconds; mean difference = 4.4 seconds; 95% confidence interval = 8.7-0.1). Blood analysis revealed significantly elevated blood buffering potential preswim (pH: BICARB = 7.48 ± 0.01, PLAC = 7.41 ± 0.01) along with a significant decrease in extracellular K+ (BICARB = 4.0 ± 0.1 mmol·L-1, PLAC = 4.6 ± 0.1 mmol·L-1). The findings suggest that 0.3 g·kg-1 NaHCO3 ingested 2.5 hours before exercise enhances the blood buffering potential and may positively influence swim performance.

Sodium bicarbonate supplementation prevents skilled tennis performance decline after a simulated match

The supplementation of sodium bicarbonate (NaHCO₃) could increase performance or delay fatigue in intermittent high-intensity exercise. Prolonged tennis matches result in fatigue, which impairs skilled performance. The aim of this study was to investigate the effect of NaHCO₃ supplementation on skilled tennis performance after a simulated match. Nine male college tennis players were recruited for this randomized cross-over, placebo-controlled, double-blind study. The participants consumed NaHCO₃ (0.3 g. kg^-1) or NaCl (0.209 g. kg^-1) before the trial. An additional supplementation of 0.1 g. kg^-1 NaHCO₃ or 0.07 g. kg^-1 NaCl was ingested after the third game in the simulated match. The Loughborough Tennis Skill Test was performed before and after the simulated match. Post-match [HCO₃^-] and base excess were significantly higher in the bicarbonate trial than those in the placebo trial. Blood [lactate] was significantly increased in the placebo (pre: 1.22 ± 0.54; post: 2.17 ± 1.46 mM) and bicarbonate (pre: 1.23 ± 0.41; post: 3.21 ± 1.89 mM) trials. The match-induced change in blood [lactate] was significantly higher in the bicarbonate trial. Blood pH remained unchanged in the placebo trial (pre: 7.37 ± 0.32; post: 7.37 ± 0.14) but was significantly increased in the bicarbonate trial (pre: 7.37 ± 0.26; post: 7.45 ± 0.63), indicating a more alkaline environment. The service and forehand ground stroke consistency scores were declined significantly after the simulated match in the placebo trial, while they were maintained in the bicarbonate trial. The match-induced declines in the consistency scores were significantly larger in the placebo trial than those in the bicarbonate trial. This study suggested that NaHCO₃ supplementation could prevent the decline in skilled tennis performance after a simulated match.

Effects of four recovery methods on repeated maximal rock climbing performance

PURPOSE

Considering the development of rock climbing as a competitive sport, we aimed at investigating the influence of four recovery methods on subsequent maximal climbing performance.

METHODS

In a randomly assigned crossover design, 13 female well-trained climbers (27.1 +/- 8.9 yr) came to the climbing center on four occasions separated by 1 wk. On each occasion, they had to perform two climbing tests (C1 and C2) until volitional exhaustion on a prepracticed route (overhanging wall, level 6b). These two tests were separated by 20 min of recovery. Four recovery methods were used in randomized order: passive recovery, active recovery (cycle ergometer, 30-40 W), electromyostimulation on the forearm muscles (bisymmetric TENS current), or cold water immersion of the forearms and arms (three periods of 5 min at 15 +/- 1 degrees C). Climbing tests' performance was reflected by the number of arm movements and climb duration.

RESULTS

Using active recovery and cold water immersion, performance at C2 was maintained in comparison with C1, whereas C2 performance was impaired compared with C1 (P< 0.01) using electromyostimulation and passive recovery (recovery method-by-climb interaction, P < 0.05). Blood lactate decreased during recovery, with the greatest decrease occurring during active recovery (time-by-recovery method interaction, P < 0.001). Arms and forearms' skin temperatures were lower throughout the cold water immersion compared with the other three methods (P < 0.001).

CONCLUSION

Active recovery and cold water immersion are two means of preserving performance when repeating acute exhausting climbing trails in female climbers. These positive effects are accompanied by a greater lactate removal and a decrease in subcutaneous tissues temperatures, respectively.

Role of beta-alanine supplementation on muscle carnosine and exercise performance

In this narrative review, we present and discuss the current knowledge available on carnosine and beta-alanine metabolism as well as the effects of beta-alanine supplementation on exercise performance. Intramuscular acidosis has been attributed to be one of the main causes of fatigue during intense exercise. Carnosine has been shown to play a significant role in muscle pH regulation. Carnosine is synthesized in skeletal muscle from the amino acids l-histidine and beta-alanine. The rate-limiting factor of carnosine synthesis is beta-alanine availability. Supplementation with beta-alanine has been shown to increase muscle carnosine content and therefore total muscle buffer capacity, with the potential to elicit improvements in physical performance during high-intensity exercise. Studies on beta-alanine supplementation and exercise performance have demonstrated improvements in performance during multiple bouts of high-intensity exercise and in single bouts of exercise lasting more than 60 s. Similarly, beta-alanine supplementation has been shown to delay the onset of neuromuscular fatigue. Although beta-alanine does not improve maximal strength or VO2max, some aspects of endurance performance, such as anaerobic threshold and time to exhaustion, can be enhanced. Symptoms of paresthesia may be observed if a single dose higher than 800 mg is ingested. The symptoms, however, are transient and related to the increase in plasma concentration. They can be prevented by using controlled release capsules and smaller dosing strategies. No important side effect was related to the use of this amino acid so far. In conclusion, beta-alanine supplementation seems to be a safe nutritional strategy capable of improving high-intensity anaerobic performance.

Diet-induced acidosis: is it real and clinically relevant?

The concept of diet-induced ‘acidosis’ as a cause of disease has been a subject of interest for more than a century. The present article reviews the history of our evolving understanding of physiological pH, the physiological support for the concept of ‘acidosis’, the causes of acidosis, how it is recognised, its short-term effects as well as the long-term clinical relevance of preventative measures, and the research support for normalisation of pH. Further, we suggest differentiation of the terms ‘acidosis’ and ‘acidaemia’ as a way to resolve the conflation of these topics which has led to confusion and controversy. The available research makes a compelling case that diet-induced acidosis, not diet-induced acidaemia, is a real phenomenon, and has a significant, clinical, long-term pathophysiological effect that should be recognised and potentially counterbalanced by dietary means.

Moderate hypercapnia exerts beneficial effects on splanchnic energy metabolism during endotoxemia

PURPOSE

Low tidal volume ventilation and permissive hypercapnia are required in patients with sepsis complicated by ARDS. The effects of hypercapnia on tissue oxidative metabolism in this setting are unknown. We therefore determined the effects of moderate hypercapnia on markers of systemic and splanchnic oxidative metabolism in an animal model of endotoxemia.

METHODS

Anesthetized rats maintained at a PaCO(2) of 30, 40 or 60 mmHg were challenged with endotoxin. A control group (PaCO(2) 40 mmHg) received isotonic saline. Hemodynamic variables, arterial lactate, pyruvate, and ketone bodies were measured at baseline and after 4 h. Tissue adenosine triphosphate (ATP) and lactate were measured in the small intestine and the liver after 4 h.

RESULTS

Endotoxin resulted in low cardiac output, increased lactate/pyruvate ratio and decreased ketone body ratio. These changes were not influenced by hypercapnia, but were more severe with hypocapnia. In the liver, ATP decreased and lactate increased independently from PaCO(2) after endotoxin. In contrast, the drop of ATP and the rise in lactate triggered by endotoxin in the intestine were prevented by hypercapnia.

CONCLUSIONS

During endotoxemia in rats, moderate hypercapnia prevents the deterioration of tissue energetics in the intestine.

Muscle metabolism and acid-base status during exercise in forearm work-related myalgia measured with31P-MRS

In this study, we examined muscle metabolic and acid-base status during incremental wrist extension exercise in the forearm of individuals with work-related myalgia (WRM). Eighteen women employed in full-time occupations involving repetitive forearm labor were recruited in this cross-sectional study. Nine of these women were diagnosed with WRM, while the other nine had no previous WRM history and were used as age-matched controls (Con). Phosphorus-31 magnetic resonance spectroscopy (31P-MRS) was used to noninvasively monitor the intracellular concentrations of phosphocreatine ([PCr]) and inorganic phosphate ([Pi]) as well as intracellular pH (pHi) status during exercise in WRM and Con. We observed a 38% decreased work capacity in WRM compared with Con [0.18 W (SD 0.03) vs. 0.28 W (SD 0.10); P = 0.007]. Piecewise linear regression of the incremental exercise data revealed that the onset of a faster decrease in pHi(i.e., the pH threshold, pHT) and the onset of a faster increase in log([Pi]/[PCr]) (i.e., the phosphorylation threshold, PT) occurred at a 14% relatively lower power output in WRM [pHT: 45.2% (SD 5.3) vs. 59.0% (SD 4.6), P < 0.001; PT: 44.8% (SD 4.3) vs. 57.8% (SD 3.1), P < 0.001; % of peak power output, Con vs. WRM, respectively]. Monoexponential modeling of the kinetics of [PCr] and pHirecovery following exercise demonstrated a slower ( P = 0.005) time constant (τ) for [PCr] in WRM [113 s (SD 25)] vs. Con [77 s (SD 23)] and a slower ( P = 0.007) τ for pHiin WRM [370 s (SD 178)] vs. Con [179 s (SD 52)]. In conclusion, our results suggest that WRM is associated with an increased reliance on nonoxidative metabolism. Possible mechanisms include a reduction in local muscle blood flow and perfusion, an increased ATP cost of force production, or both.

Ergogenic effects of sodium bicarbonate

Athletes use many different strategies to enhance their performance, including clothing and footwear, training regimes, diets, and ergogenic aids. The use of ergogenic aids is believed to be widespread, with a variety of legal as well as illegal substances being used previously and currently. Among the more popular ergogenic aids is the use of sodium bicarbonate or sodium citrate, collectively recognized as "buffers." These substances potentially provide the body with added resistance against fatigue caused by deleterious changes in acid-base balance brought about by a variety of exercise modes and durations. The popularity of buffering has generated a plethora of research dating back to the 1930s, which continues to date. The issues surrounding buffering revolve around the dosage size, timing of ingestion, and the type of exercise to benefit from the use of buffers. We hope this review addresses these pertinent issues.

Accurate work-rate measurements during in vivo MRS studies of exercising human quadriceps

INTRODUCTION

Given that we have reached a point in the field of muscle energetics where absolute measurements are warranted to take the area forward, we designed an ergometer, including two force and two displacement transducers, allowing dynamic and isometric knee extension within a MR system and accurate measurements of power output.

METHODS

On the basis of repeated measurements, the force and displacement transducers accuracy was 1% for values ranging from 0 to 394 N and 4% for values ranging from 0 to 20 cm. In addition, measurements were not affected by magnetic field. MRS experiments in exercising muscle were conducted in eight subjects. They performed two standardized dynamic alternate leg extension exercises (25 and 35% of MVC) while the corresponding metabolic changes were measured using (31)P-MRS.

RESULTS

The mean power output produced during both exercises were 63 +/- 16 and 81 +/- 15 W while the eccentric work was reduced i.e. 12 +/- 14 and 21 +/- 6 W for the moderate and heavy exercise respectively. The corresponding metabolic changes were significant with a 20-40% PCr depletion and an end of exercise pH ranging from 0.02 to 0.70 pH units.

CONCLUSION

Overall, the present ergometer allows quadriceps exercise in a MR system and should be useful for future metabolic studies for which reliable and absolute quantification of power output is warranted.

β-Alanine supplementation augments muscle carnosine content and attenuates fatigue during repeated isokinetic contraction bouts in trained sprinters

Carnosine (β-alanyl-l-histidine) is present in high concentrations in human skeletal muscle. The ingestion of β-alanine, the rate-limiting precursor of carnosine, has been shown to elevate the muscle carnosine content. We aimed to investigate, using proton magnetic resonance spectroscopy (proton MRS), whether oral supplementation with β-alanine during 4 wk would elevate the calf muscle carnosine content and affect exercise performance in 400-m sprint-trained competitive athletes. Fifteen male athletes participated in a placebo-controlled, double-blind study and were supplemented orally for 4 wk with either 4.8 g/day β-alanine or placebo. Muscle carnosine concentration was quantified in soleus and gastrocnemius by proton MRS. Performance was evaluated by isokinetic testing during five bouts of 30 maximal voluntary knee extensions, by endurance during isometric contraction at 45% maximal voluntary contraction, and by the indoor 400-m running time. β-Alanine supplementation significantly increased the carnosine content in both the soleus (+47%) and gastrocnemius (+37%). In placebo, carnosine remained stable in soleus, while a small and significant increase of +16% occurred in gastrocnemius. Dynamic knee extension torque during the fourth and fifth bout was significantly improved with β-alanine but not with placebo. Isometric endurance and 400-m race time were not affected by treatment. In conclusion, 1) proton MRS can be used to noninvasively quantify human muscle carnosine content; 2) muscle carnosine is increased by oral β-alanine supplementation in sprint-trained athletes; 3) carnosine loading slightly but significantly attenuated fatigue in repeated bouts of exhaustive dynamic contractions; and 4) the increase in muscle carnosine did not improve isometric endurance or 400-m race time.

Effects of extracellular HCO3(-) on fatigue, pHi, and K+ efflux in rat skeletal muscles

Elevated plasma HCO(3)(-) can improve exercise endurance in humans. This effect has been related to attenuation of the work-induced reduction in muscle pH, which is suggested to improve performance via at least two mechanisms: 1) less inhibition of muscle enzymes and 2) reduced opening of muscle K(ATP) channels with less ensuing reduction in excitability. Aiming at determining whether the ergogenic effect of HCO(3)(-) is related to effects on muscles, we examined the effect of elevating extracellular HCO(3)(-) from 25 to 40 mM (pH from 7.4 to 7.6) on fatigue, intracellular pH (pH(i)), and K(+) efflux in isolated rat skeletal muscles contracting isometrically. Fatigue induced by 30-Hz stimulation at 30 and 37 degrees C was similar between soleus muscles incubated in high and normal HCO(3)(-) concentrations. In extensor digitorum longus muscles stimulated at 60 Hz, elevated HCO(3)(-) did not affect fatigue at 30 degrees C. In soleus muscles, 30-Hz stimulation induced a approximately 0.2 unit reduction in pH(i), as determined by using the pH-sensitive probe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. This reduction in pH(i) was not affected by elevated HCO(3)(-). Estimation of K(+) efflux using (86)Rb(+) showed that elevated HCO(3)(-) did not affect K(+) efflux at rest or during contractions. Similarly, other modifications of the intra- and extracellular pH had little effect on K(+) efflux during contraction. In conclusion, elevated extracellular HCO(3)(-) had no significant effect on muscle fatigue, pH(i), and K(+) efflux. These findings indicate that alternative mechanisms must be considered for the ergogenic effect of HCO(3)(-) observed in integral exercise studies.

Prior exercise delays the onset of acidosis during incremental exercise

The effects of prior moderate- and prior heavy-intensity exercise on the subsequent metabolic response to incremental exercise were examined. Healthy, young adult subjects (n = 8) performed three randomized plantar-flexion exercise tests: 1) an incremental exercise test (approximately 0.6 W/min) to volitional fatigue (Ramp); 2) Ramp preceded by 6 min of moderate-intensity, constant-load exercise below the intracellular pH threshold (pHT; Mod-Ramp); and 3) Ramp preceded by 6 min of heavy-intensity, constant-load exercise above pHT (Hvy-Ramp); the constant-load and incremental exercise periods were separated by 6 min of rest. (31)P-magnetic resonance spectroscopy was used to continuously monitor intracellular pH, phosphocreatine concentration ([PCr]), and inorganic phosphate concentration ([P(i)]). No differences in exercise performance or the metabolic response to exercise were observed between Ramp and Mod-Ramp. However, compared with Ramp, a 14% (SD 10) increase (P < 0.01) in peak power output (PPO) was observed in Hvy-Ramp. The improved exercise performance in Hvy-Ramp was accompanied by a delayed (P = 0.01) onset of intracellular acidosis [Hvy-Ramp 60.4% PPO (SD 11.7) vs. Ramp 45.8% PPO (SD 9.4)] and a delayed (P < 0.01) onset of rapid increases in [P(i)]/[PCr] [Hvy-Ramp 61.5% PPO (SD 12.0) vs. Ramp 45.1% PPO (SD 9.1)]. In conclusion, prior heavy-intensity exercise delayed the onset of intracellular acidosis and enhanced exercise performance during a subsequent incremental exercise test.

Sodium Bicarbonate Ingestion Alters the Slow but Not the Fast Phase of V˙O2 Kinetics

PURPOSE

The influence of metabolic alkalosis (ALK) on pulmonary O2 uptake (pVO2) kinetics during high-intensity cycle exercise is controversial. The purpose of this study was to examine the influence of ALK induced by sodium bicarbonate (NaHCO3) ingestion on pVO2 kinetics, using a sufficient number of repeat-step transitions to provide high confidence in the results obtained.

METHODS

Seven healthy males completed step tests to a work rate requiring 80% pVO2max on six separate occasions: three times after ingestion of 0.3 g x kg(-1) body mass NaHCO3 in 1 L of fluid, and three times after ingestion of a placebo (CON). Blood samples were taken to assess changes in acid-base balance, and pVO2 was measured breath-by-breath.

RESULTS

NaHCO3 ingestion significantly increased blood pH and [bicarbonate] both before and during exercise relative to the control condition (P < 0.001). The time constant of the phase II pVO2 response was not different between conditions (CON: 29 +/- 6 vs ALK: 32 +/- 7 s; P = 0.21). However, the onset of the pVO2 slow component was delayed by NaHCO3 ingestion (CON: 120 +/- 19 vs ALK: 147 +/- 34 s; P < 0.01), resulting in a significantly reduced end-exercise pVO2 (CON: 2.88 +/- 0.19 vs ALK: 2.79 +/- 0.23 L x min(-1); P < 0.05).

CONCLUSIONS

Metabolic alkalosis has no effect on phase II pVO2 kinetics but alters the pVO2 slow-component response, possibly as a result of the effects of NaHCO3 ingestion on muscle pH.

Lactic acid and exercise performance : culprit or friend?

This article critically discusses whether accumulation of lactic acid, or in reality lactate and/or hydrogen (H+) ions, is a major cause of skeletal muscle fatigue, i.e. decline of muscle force or power output leading to impaired exercise performance. There exists a long history of studies on the effects of increased lactate/H+ concentrations in muscle or plasma on contractile performance of skeletal muscle. Evidence suggesting that lactate/H+ is a culprit has been based on correlation-type studies, which reveal close temporal relationships between intramuscular lactate or H+ accumulation and the decline of force during fatiguing stimulation in frog, rodent or human muscle. In addition, an induced acidosis can impair muscle contractility in non-fatigued humans or in isolated muscle preparations, and several mechanisms to explain such effects have been provided. However, a number of recent high-profile papers have seriously challenged the 'lactic acid hypothesis'. In the 1990s, these findings mainly involved diminished negative effects of an induced acidosis in skinned or intact muscle fibres, at higher more physiological experimental temperatures. In the early 2000s, it was conclusively shown that lactate has little detrimental effect on mechanically skinned fibres activated by artificial stimulation. Perhaps more remarkably, there are now several reports of protective effects of lactate exposure or induced acidosis on potassium-depressed muscle contractions in isolated rodent muscles. In addition, sodium-lactate exposure can attenuate severe fatigue in rat muscle stimulated in situ, and sodium lactate ingestion can increase time to exhaustion during sprinting in humans. Taken together, these latest findings have led to the idea that lactate/H+ is ergogenic during exercise. It should not be taken as fact that lactic acid is the deviant that impairs exercise performance. Experiments on isolated muscle suggest that acidosis has little detrimental effect or may even improve muscle performance during high-intensity exercise. In contrast, induced acidosis can exacerbate fatigue during whole-body dynamic exercise and alkalosis can improve exercise performance in events lasting 1-10 minutes. To reconcile the findings from isolated muscle fibres through to whole-body exercise, it is hypothesised that a severe plasma acidosis in humans might impair exercise performance by causing a reduced CNS drive to muscle.

Effects of chronic NaHCO3 ingestion during interval training on changes to muscle buffer capacity, metabolism, and short-term endurance performance

This study determined the effects of altering the H(+) concentration during interval training, by ingesting NaHCO(3) (Alk-T) or a placebo (Pla-T), on changes in muscle buffer capacity (beta m), endurance performance, and muscle metabolites. Pre- and posttraining peak O(2) uptake (V(O2 peak)), lactate threshold (LT), and time to fatigue at 100% pretraining V(O2 peak) intensity were assessed in 16 recreationally active women. Subjects were matched on the LT, were randomly placed into the Alk-T (n = 8) or Pla-T (n = 8) groups, and performed 8 wk (3 days/wk) of six to twelve 2-min cycle intervals at 140-170% of their LT, ingesting NaHCO(3) or a placebo before each training session (work matched between groups). Both groups had improvements in beta m (19 vs. 9%; P < 0.05) and V(O2 peak) (22 vs. 17%; P < 0.05) after the training period, with no differences between groups. There was a significant correlation between pretraining beta m and percent change in beta m (r = -0.70, P < 0.05). There were greater improvements in both the LT (26 vs. 15%; P = 0.05) and time to fatigue (164 vs. 123%; P = 0.05) after Alk-T, compared with Pla-T. There were no changes to pre- or postexercise ATP, phosphocreatine, creatine, and intracellular lactate concentrations, or pH(i) after training. Our findings suggest that training intensity, rather than the accumulation of H(+) during training, may be more important to improvements in beta m. The group ingesting NaHCO(3) before each training session had larger improvements in the LT and endurance performance, possibly because of a reduced metabolic acidosis during training and a greater improvement in muscle oxidative capacity.

Alkalosis increases muscle K+ release, but lowers plasma [K+] and delays fatigue during dynamic forearm exercise

Alkalosis enhances human exercise performance, and reduces K+ loss in contracting rat muscle. We investigated alkalosis effects on K+ regulation, ionic regulation and fatigue during intense exercise in nine untrained volunteers. Concentric finger flexions were conducted at 75% peak work rate (3 W) until fatigue, under alkalosis (Alk, NaHCO3, 0.3 g kg(-1)) and control (Con, CaCO3) conditions, 1 month apart in a randomised, double-blind, crossover design. Deep antecubital venous (v) and radial arterial (a) blood was drawn at rest, during exercise and recovery, to determine arterio-venous differences for electrolytes, fluid shifts, acid-base and gas exchange. Finger flexion exercise barely perturbed arterial plasma ions and acid-base status, but induced marked arterio-venous changes. Alk elevated [HCO3-] and PCO2, and lowered [H+] (P < 0.05). Time to fatigue increased substantially during Alk (25 +/- 8%, P < 0.05), whilst both [K+]a and [K+]v were reduced (P < 0.01) and [K+]a-v during exercise tended to be greater (P= 0.056, n= 8). Muscle K+ efflux at fatigue was greater in Alk (21.2+/- 7.6 micromol min(-1), 32 +/- 7%, P < 0.05, n= 6), but peak K+ uptake rate was elevated during recovery (15 +/- 7%, P < 0.05) suggesting increased muscle Na+,K+-ATPase activity. Alk induced greater [Na+]a, [Cl-]v, muscle Cl- influx and muscle lactate concentration ([Lac-]) efflux during exercise and recovery (P < 0.05). The lower circulating [K+] and greater muscle K+ uptake, Na+ delivery and Cl- uptake with Alk, are all consistent with preservation of membrane excitability during exercise. This suggests that lesser exercise-induced membrane depolarization may be an important mechanism underlying enhanced exercise performance with Alk. Thus Alk was associated with improved regulation of K+, Na+, Cl- and Lac-.

Characteristics of a MR-compatible ankle exercise ergometer for a 3.0 T head-only MR scanner

An exercise ergometer, for isometric or dynamic contraction of both dorsiflexion and/or plantarflexion exercise, was designed and constructed for a 3.0 T head-only MR scanner. The principal features of this MR-compatible ergometer include electronic devices for quantification of force (during isometric exercise) and angular displacement (during dynamic exercise), without any significant losses to external motions or frictions. The ergometer was also made to be adjustable for subject leg length and was designed for suspension within the bore of the magnet to eliminate transmission of force and vibration to the MR scanner. A description of the design and construction, as well as the important technical features, is presented herein.

Methodological approaches to the study of metabolism across individual tissues in man

PURPOSE OF REVIEW

This article is intended to briefly overview available methodological approaches for the study of regional metabolism in man in vivo, and to summarize recent advances in this field of research.

RECENT FINDINGS

Several methods have been developed and currently allow for the qualitative and quantitative assessment of energy interconversions and substrate fluxes across individual tissues of man, including the measurement of arteriovenous concentration differences, microdialysis, and nuclear magnetic resonance spectroscopy of carbon, hydrogen, and phosphorus isotopes. Each method alone has been used rather extensively to examine certain aspects of organ and tissue metabolism under a variety of experimental conditions, and has contributed novel information in this regard. The most exciting development appears to be the combined use of more than one investigational technique, across one or more tissues simultaneously. A handful of recent studies have employed complex experimental designs or hybrid methodologies, ultimately demonstrating the potential for a more detailed assessment of metabolism at the local level.

SUMMARY

Clearly, advances in the use, performance, and applications of available methods are expected to provide improved and more powerful tools for the metabolic investigation of organs and tissues in humans in vivo.

NaHCO3-induced alkalosis reduces the phosphocreatine slow component during heavy-intensity forearm exercise

During heavy-intensity exercise, the mechanisms responsible for the continued slow decline in phosphocreatine concentration ([PCr]) (PCr slow component) have not been established. In this study, we tested the hypothesis that a reduced intracellular acidosis would result in a greater oxidative flux and, consequently, a reduced magnitude of the PCr slow component. Subjects (n = 10) performed isotonic wrist flexion in a control trial and in an induced alkalosis (Alk) trial (0.3g/kg oral dose of NaHCO3, 90 min before testing). Wrist flexion, at a contraction rate of 0.5 Hz, was performed for 9 min at moderate- (75% of onset of acidosis; intracellular pH threshold) and heavy-intensity (125% intracellular pH threshold) exercise. 31P-magnetic resonance spectroscopy was used to measure intracellular [H+], [PCr], [Pi], and [ATP]. The initial recovery data were used to estimate the rate of ATP synthesis and oxidative flux at the end of heavy-intensity exercise. In repeated trials, venous blood sampling was used to measure plasma [H+], [HCO3-], and [Lac-]. Throughout rest and exercise, plasma [H+] was lower (P < 0.05) and [HCO3-] was elevated (P < 0.05) in Alk compared with control. During the final 3 min of heavy-intensity exercise, Alk caused a lower (P < 0.05) intracellular [H+] [246 (SD 117) vs. 291 nmol/l (SD 129)], a greater (P < 0.05) [PCr] [12.7 (SD 7.0) vs. 9.9 mmol/l (SD 6.0)], and a reduced accumulation of [ADP] [0.065 (SD 0.031) vs. 0.098 mmol/l (SD 0.059)]. Oxidative flux was similar (P > 0.05) in the conditions at the end of heavy-intensity exercise. In conclusion, our results are consistent with a reduced intracellular acidosis, causing a decrease in the magnitude of the PCr slow component. The decreased PCr slow component in Alk did not appear to be due to an elevated oxidative flux.