Acidosis, but Not Alkalosis, Affects Anaerobic Metabolism and Performance in a 4-km Time Trial

Lactic acidosis: implications for human exercise performance

During high-intensity exercise a lactic-acidosis occurs with raised myoplasmic and plasma concentrations of lactate- and protons ([lactate-], [H+] or pH). We critically evaluate whether this causes/contributes to fatigue during human exercise. Increases of [lactate-] per se (to 25 mM in plasma, 50 mM intracellularly) exert little detrimental effect on muscle performance while ingestion/infusion of lactate- can be ergogenic. An exercise-induced intracellular acidosis at the whole-muscle level (pHi falls from 7.1-7.0 to 6.9-6.3), incorporates small changes in slow-twitch fibres (pHi ~ 6.9) and large changes in fast-twitch fibres (pHi ~ 6.2). The relationship between peak force/power and acidosis during fatiguing contractions varies across exercise regimes implying that acidosis is not the sole cause of fatigue. Concomitant changes of other putative fatigue factors include phosphate metabolites, glycogen, ions and reactive oxygen species. Acidosis to pHi 6.7-6.6 at physiological temperatures (during recovery from exercise or induced in non-fatigued muscle), has minimal effect on force/power. Acidosis to pHi ~ 6.5-6.2 per se reduces maximum force (~12%), slows shortening velocity (~5%), and lowers peak power (~22%) in non-fatigued muscles/individuals. A pre-exercise induced-acidosis with ammonium chloride impairs exercise performance in humans and accelerates the decline of force/power (15-40% initial) in animal muscles stimulated repeatedly in situ. Raised [H+]i and diprotonated inorganic phosphate ([H2PO4-]i) act on myofilament proteins to reduce maximum cross-bridge activity, Ca2+-sensitivity, and myosin ATPase activity. Acidosis/[lactate-]o attenuates detrimental effects of large K+-disturbances on action potentials and force in non-fatigued muscle. We propose that depressive effects of acidosis and [H2PO4-]i on myofilament function dominate over the protective effects of acidosis/lactate- on action potentials during fatigue. Raised extracellular [H+]/[lactate-] do not usually cause central fatigue but do contribute to elevated perceived exertion and fatigue sensations by activating group III/IV muscle afferents. Modulation of H+/lactate- regulation (via extracellular H+-buffers, monocarboxylate transporters, carbonic anhydrase, carnosine) supports a role for intracellular acidosis in fatigue. In conclusion, current evidence advocates that severe acidosis in fast-twitch fibres can contribute to force/power fatigue during intense human exercise.

The Effects of a Novel Sodium Bicarbonate Ingestion System on Repeated 4 km Cycling Time Trial Performance in Well-Trained Male Cyclists

BACKGROUND

A novel sodium bicarbonate (SB) product has come to market named the "Bicarb System" (M-SB; Maurten AB, Gothenburg, Sweden). It claims to minimise gastrointestinal (GI) discomfort whilst still improving exercise performance.

AIM

To investigate the effects of M-SB ingestion on repeated 4 km cycling time trials (TT1 and TT2) in well-trained male cyclists.

METHODS

The study recruited ten well-trained cyclists (maximal oxygen uptake (V ˙ O 2 max ): 67 ± 4 ml kg-1 min-1 BM; peak power output (PPO) atV ˙ O 2 max : 423 ± 21 W) to take part in this randomised, crossover and double-blinded study. Following one visit to determineV ˙ O 2 max , participants completed a second visit to identify individual time to peak blood bicarbonate (HCO3-) (ITTP) in a rested state. Visit three was a familiarisation trial mimicking the experimental procedures. Visits four to seven consisted of completing 2 × 4 km cycling TTs separated by 45 min passive recovery, following one of either: 0.3 g kg-1 BM M-SB, 0.21 g kg-1 BM sodium chloride (placebo; PLA) in vegetarian capsules (size 00), or a control trial (CON). Supplements (M-SB or placebo) were ingested pre-exercise at their respective ITTP.

RESULTS

Performance in TT1 was faster in the M-SB condition compared with TT1 in CON (- 5.1 s; p = 0.004) and PLA (- 3.5 s; p < 0.001). In TT2, performance was also significantly faster in the M-SB condition compared with CON (- 4.4 s; p = 0.018) or PLA (- 4.1 s; p = 0.002). Total aggregated GI symptoms were generally low and not significantly different between PLA and the M-SB conditions for a range of symptoms.

CONCLUSIONS

The ingestion of M-SB improves repeated 4 km cycling TT performance and the recovery of acid-base balance between bouts, whilst causing minimal GI discomfort.

Sodium bicarbonate induces alkalosis, but improves high-intensity cycling performance only when participants expect a beneficial effect: a placebo and nocebo study

The study aimed to investigate the effects of sodium bicarbonate (NaHCO3) intake with divergent verbal and visual information on constant load cycling time-to-task failure, conducted within the severe intensity domain. Fifteen recreational cyclists participated in a randomized double-blind, crossover study, ingesting NaHCO3 or placebo (i.e., dextrose), but with divergent information about its likely influence (i.e., likely to induce ergogenic, inert, or harmful effects). Performance was evaluated using constant load cycling time to task failure trial at 115% of peak power output estimated during a ramp incremental exercise test. Data on blood lactate, blood acid-base balance, muscle electrical activity (EMG) through electromyography signal, and the twitch interpolation technique to assess neuromuscular indices were collected. Despite reduced peak force in the isometric maximal voluntary contraction and post-effort peripheral fatigue in all conditions (P < 0.001), neither time to task failure, EMG nor, blood acid-base balance differed between conditions (P > 0.05). Evaluation of effect sizes of all conditions suggested that informing participants that the supplement would be likely to have a positive effect (NaHCO3/Ergogenic: 0.46; 0.15-0.74; Dextrose/Ergogenic: 0.45; 0.04-0.88) resulted in improved performance compared to control. Thus, NaHCO3 ingestion consistently induced alkalosis, indicating that the physiological conditions to improve performance were present. Despite this, NaHCO3 ingestion did not influence performance or indicators of neuromuscular fatigue. In contrast, effect size estimates indicate that participants performed better when informed that they were ingesting an ergogenic supplement. These findings suggest that the apparently ergogenic effect of NaHCO3 may be due, at least in part, to a placebo effect.

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.

Acute effects of sodium bicarbonate ingestion on cycling time-trial performance: A systematic review and meta-analysis of randomized controlled trials

This study aimed to investigate the isolated effects of NaHCO₃ on cycling time-trial performance. Furthermore, we investigated whether the ingestion time of NaHCO₃, standardized or individualized based on time to peak, could be effective in improving cycling time-trial performance. A systematic review was carried out on randomized placebo-controlled studies. A random-effects meta-analysis assessed the standardized mean difference (SMD) between NaHCO₃ and placebo conditions. Eighteen studies were qualitatively (systematic review) and quantitatively (meta-analysis) analysed concerning mean power output (W_mean) (n = 182) and time performance (n = 201). The reviewed studies showed a low risk of bias and homogenous results for W_mean (I² = 0%) and performance time (I²= 0%). Overall, when compared to placebo, the NaHCO₃ ingestion improved the W_mean (SMD: 0.42; 95% CI: 0.21-0.63; P = 0.001) and performance time (SMD: 0.22; 95% CI: 0.02-0.43; P = 0.03). Similarly, the NaHCO₃ ingestion using a time-to-peak strategy improved the W_mean (SMD: 0.39; 95% CI: 0.03-0.75; P = 0.04; I²= 15%) and performance time (SMD: 0.34; 95% CI: 0.07-0.61, P = 0.01, I²= 0%). The present findings reveal that NaHCO₃ ingestion has the potential to increase the overall performance time and W_mean in cycling time trials. HighlightsNaHCO₃ is an effective strategy to increase cycling time-trial performance.The standardized protocol did not improve the cycling time-trial performance parameters.The individualized time-to-peak NaHCO₃ ingestion has a positive effect on time and W_mean during cycling time-trial performance.

Caffeine Combined With Sodium Bicarbonate Improves Pacing and Overall Performance During a High-Intensity Time Trial

Background: No study has demonstrated the effects of sodium bicarbonate plus caffeine (NaHCO₃ + CAF) on power output (PO) distribution (e.g., pacing), physiological parameters and energy system contribution during a 4-km cycling time trial (TT). Thus, we aimed to investigate the effects of NaHCO₃ + CAF on pacing, physiological parameters, and energy system contribution during a 4-km cycling TT. Methods: Using a double-blind and counterbalanced design, 10 cyclists performed three ingestion protocols (NaHCO₃ + CAF, NaHCO₃ and placebo) followed by a 4-km cycling TT. Results: 100 min after substance ingestion, the magnitude of change in blood pH and bicarbonate concentration [HCO₃^-] for NaHCO₃ + CAF (+0.04 ± 0.03 and +5.9 ± 1.6 mmol·L^-1, respectively, P < .05) and NaHCO₃ (+0.02 ± 0.03 and +4.1 ± 2.0 mmol·L^-1, respectively, P < .05) was more pronounced than in placebo (-0.01 ± 0.02 and 0.4 ± 0.9 mmol·L^-1, respectively). The increase in plasma lactate concentration was more pronounced in NaHCO₃ + CAF than in NaHCO₃ and placebo (P < .05). Mean ventilation and carbon dioxide production were higher in NaHCO₃ + CAF compared to NaHCO₃ and placebo (P < .05). The PO and anaerobic power output were increased at the beginning of the 4-km TT (P < .05) in NaHCO₃ + CAF compared to the other two conditions, resulting in an improved overall performance (P < .05). Conclusion: NaHCO₃ + CAF results in a higher PO and increased anaerobic contribution and respiratory parameters during a 4-km cycling TT.

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.

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.

Effect of Warm-Up and Sodium Bicarbonate Ingestion on 4-km Cycling Time-Trial Performance

PURPOSE

To examine whether an ecologically valid, intermittent, sprint-based warm-up strategy impacted the ergogenic capacity of individualized sodium bicarbonate (NaHCO3) ingestion on 4-km cycling time-trial (TT) performance.

METHODS

A total of 8 male cyclists attended 6 laboratory visits for familiarization, determination of time to peak blood bicarbonate, and 4 × 4-km cycling TTs. Experimental beverages were administered doubleblind. Treatments were conducted in a block-randomized, crossover order: intermittent warm-up + NaHCO3 (IWSB), intermittent warm-up + placebo, control warm-up + NaHCO3 (CWSB), and control warm-up + placebo (CWP). The intermittent warm-up comprised exercise corresponding to lactate threshold (5 min at 50%, 2 min at 60%, 2 min at 80%, 1 min at 100%, and 2 min at 50%) and 3 × 10-second maximal sprints. The control warm-up comprised 16.5 minutes cycling at 150 W. Participants ingested 0.3 g·kg body mass-1 NaHCO3 or 0.03 g·kg body mass-1 sodium chloride (placebo) in 5 mL·kg body mass-1 fluid (3:2, water and sugar-free orange squash). Paired t tests were conducted for TT performance. Hematological data (blood bicarbonate and blood lactate) and gastrointestinal discomfort were analyzed using repeated-measures analysis of variance.

RESULTS

Performance was faster for CWSB versus IWSB (5.0 [6.1] s; P = .052) and CWP (5.8 [6.0] s; P = .03). Pre-TT bicarbonate concentration was elevated for CWSB versus IWSB (+9.3 mmol·L-1; P < .001) and CWP (+7.1 mmol·L-1; P < .001). Post-TT blood lactate concentration was elevated for CWSB versus CWP (+2.52 mmol·L-1; P = .022). Belching was exacerbated pre-warm-up for IWSB versus intermittent warm-up +placebo (P = .046) and CWP (P = .027).

CONCLUSION

An intermittent, sprint-based warm-up mitigated the ergogenic benefits of NaHCO3 ingestion on 4-km cycling TT performance.

Effect of sodium bicarbonate contribution on energy metabolism during exercise: a systematic review and meta-analysis

Background

The effects of sodium bicarbonate (NaHCO₃) on anaerobic and aerobic capacity are commonly acknowledged as unclear due to the contrasting evidence thus, the present study analyzes the contribution of NaHCO₃ to energy metabolism during exercise.

Methods

Following a search through five databases, 17 studies were found to meet the inclusion criteria. Meta-analyses of standardized mean differences (SMDs) were performed using a random-effects model to determine the effects of NaHCO₃ supplementation on energy metabolism. Subgroup meta-analyses were conducted for the anaerobic-based exercise (assessed by changes in pH, bicarbonate ion [HCO₃⁻], base excess [BE] and blood lactate [BLa]) vs. aerobic-based exercise (assessed by changes in oxygen uptake [VO₂], carbon dioxide production [VCO₂], partial pressure of oxygen [PO₂] and partial pressure of carbon dioxide [PCO₂]).

Results

The meta-analysis indicated that NaHCO₃ ingestion improves pH (SMD = 1.38, 95% CI: 0.97 to 1.79, P < 0.001; I² = 69%), HCO₃⁻ (SMD = 1.63, 95% CI: 1.10 to 2.17, P < 0.001; I² = 80%), BE (SMD = 1.67, 95% CI: 1.16 to 2.19, P < 0.001, I² = 77%), BLa (SMD = 0.72, 95% CI: 0.34 to 1.11, P < 0.001, I² = 68%) and PCO₂ (SMD = 0.51, 95% CI: 0.13 to 0.90, P = 0.009, I² = 0%) but there were no differences between VO₂, VCO₂ and PO₂ compared with the placebo condition.

Conclusions

This meta-analysis has found that the anaerobic metabolism system (AnMS), especially the glycolytic but not the oxidative system during exercise is affected by ingestion of NaHCO₃. The ideal way is to ingest it is in a gelatin capsule in the acute mode and to use a dose of 0.3 g•kg^− 1 body mass of NaHCO₃ 90 min before the exercise in which energy is supplied by the glycolytic system.

Caffeine Ingestion Affects Performance in Different Parts of a Novel Multidirectional High-Intensity Intermittent Exercise in Futsal Athletes

Objective: No study has analyzed the effects of caffeine ingestion on performance during a multidirectional high-intensity intermittent exercise. Thus, we aimed to investigate the effects of caffeine ingestion during a novel repeated agility test in futsal athletes.Methods: Using a double-blind, counterbalanced, and repeated-measures design, ten athletes (mass 71.2 ± 8.7 kg, height 1.77 ± 0.05 m, body mass index 22.7 ± 1.9 km/m², body fat percentage 10.2 ± 3.7%) performed a novel repeated-bout agility test 60 min after ingesting 6 mg · kg^-1 of caffeine or cellulose (placebo).Results: Performance time decreased progressively throughout the trial in both conditions (P = 0.01; η_p² = 0.66), with a significant interaction effect (P = 0.01; η_p² = 0.35) showing a potential beneficial effect of caffeine at the beginning, followed by a decrease at the end of the test. Furthermore, magnitude of decrease in performance was more pronounced in caffeine (-9.0 ± 5.7%) compared with placebo (-4.7 ± 3.9%, P = 0.01; d = 0.88). Interestingly, magnitude-based inferences revealed a possible benefit (70%) of caffeine at the beginning, followed by likely (93%) to very likely (96%) impairments in performance during the last third of the test. Heart rate and rating of perceived effort increased in both conditions over the time (P < 0.05), with similar values between experimental conditions (P > 0.05).Conclusion: Caffeine seems to have a potential beneficial effect at the beginning, with an impaired performance during the final third of a new multidirectional high-intensity intermittent exercise in futsal athletes.

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.

Performance Enhancing Effect of Metabolic Pre-conditioning on Upper-Body Strength-Endurance Exercise

High systemic blood lactate (La) was shown to inhibit glycolysis and to increase oxidative metabolism in subsequent anaerobic exercise. Aim of this study was to examine the effect of a metabolic pre-conditioning (MPC) on net La increase and performance in subsequent pull-up exercise (PU). Nine trained students (age: 25.1 ± 1.9 years; BMI: 21.7 ± 1.4) performed PU on a horizontal bar with legs placed on a box (angular hanging) either without or with MPC in a randomized order. MPC was a 26.6 ± 2 s all out shuttle run. Each trial started with a 15-min warm-up phase. Time between MPC and PU was 8 min. Heart rate (HR) and gas exchange measures (VO₂, VCO₂, and VE) were monitored, La and glucose were measured at specific time points. Gas exchange measures were compared by area under the curve (AUC). In PU without MPC, La increased from 1.24 ± 0.4 to 6.4 ± 1.4 mmol⋅l^-1, whereas with MPC, PU started at 9.28 ± 1.98 mmol⋅l^-1 La which increased to 10.89 ± 2.13 mmol⋅l^-1. With MPC, net La accumulation was significantly reduced by 75.5% but performance was significantly increased by 1 rep (4%). Likewise, net oxygen uptake VO₂ (50% AUC), pulmonary ventilation (VE) (34% AUC), and carbon dioxide VCO₂ production (26% AUC) were significantly increased during PU but respiratory exchange ratio (RER) was significantly blunted during work and recovery. MPC inhibited glycolysis and increased oxidative metabolism and performance in subsequent anaerobic upper-body strength-endurance exercise.

Time to Optimize Supplementation: Modifying Factors Influencing the Individual Responses to Extracellular Buffering Agents

Blood alkalosis, as indicated by an increased blood bicarbonate concentration and pH, has been shown to be beneficial for exercise performance. Sodium bicarbonate, sodium citrate, and sodium or calcium lactate, can all result in increased circulating bicarbonate and have all independently been shown to improve exercise capacity and performance under various circumstances. Although there is considerable evidence demonstrating the efficacy of these supplements in several sports-specific situations, it is commonly acknowledged that their efficacy is equivocal, due to contrasting evidence. Herein, we discuss the physiological and environmental factors that may modify the effectiveness of these supplements including, (i) absolute changes in circulating bicarbonate; (ii) supplement timing, (iii) the exercise task performed, (iv) monocarboxylate transporter (MCT) activity; (v) training status, and (vi) associated side-effects. The aim of this narrative review is to highlight the factors which may modify the response to these supplements, so that individuals can use this information to attempt to optimize supplementation and allow the greatest possibility of an ergogenic effect.

Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial

BACKGROUND

Low-carbohydrate, ketogenic diets cause mild, subclinical systemic acidosis. Anaerobic exercise performance is limited by acidosis. Therefore, we evaluated the hypothesis that a low-carbohydrate, ketogenic diet impairs anaerobic exercise performance, as compared to a high-carbohydrate diet.

METHODS

Sixteen men and women (BMI, 23±1 kg/m2, age 23±1 years) participated in a randomized-sequence, counterbalanced crossover study in which they underwent exercise testing after 4 days of either a low-carbohydrate, ketogenic diet (LC; <50 g/day and <10% of energy from carbohydrates) or a high-carbohydrate diet (HC; 6-10 g/kg/day carbohydrate). Dietary compliance was assessed with nutrient analysis of diet records, and with measures of urine pH and ketones. Anaerobic exercise performance was evaluated with the Wingate anaerobic cycling test and the yo-yo intermittent recovery test.

RESULTS

The diets were matched for total energy (LC: 2333±158 kcal/d; HC: 2280±160 kcal/d; P=0.65) but differed in carbohydrate content (9±1% vs. 63±2% of energy intake; P<0.001). LC resulted in lower urine pH (5.9±0.1 vs. 6.3±0.2, P=0.004) and the appearance of urine ketones in every participant. LC resulted in 7% lower peak power (801±58 watts vs. 857±61 watts, P=0.008) and 6% lower mean power (564±50 watts vs. 598±51 watts, P=0.01) during the Wingate Test. Total distance ran in the yo-yo intermittent recovery test was 15% less after LC diet (887±139 vs. 1045±145 meters, P=0.02).

CONCLUSIONS

Short-term low-carbohydrate, ketogenic diets reduce exercise performance in activities that are heavily dependent on anaerobic energy systems. These findings have clear performance implications for athletes, especially for high-intensity, short duration activities and sports.

Sodium bicarbonate ingestion increases glycolytic contribution and improves performance during simulated taekwondo combat

PURPOSE

To investigate the effect of sodium bicarbonate (NaHCO₃) on performance and estimated energy system contribution during simulated taekwondo combat.

METHODS

Nine taekwondo athletes completed two experimental sessions separated by at least 48 h. Athletes consumed 300 mg/kg body mass of NaHCO₃ or placebo (CaCO₃) 90 min before the combat simulation (three rounds of 2 min separated by 1 min passive recovery), in a double-blind, randomized, repeated-measures crossover design. All simulated combat was filmed to quantify the time spent fighting in each round. Lactate concentration [La^-] and rating of perceived exertion (RPE) were measured before and after each round, whereas heart rate (HR) and the estimated contribution of the oxidative (W_OXI), ATP (adenosine triphosphate)-phosphocreatine (PCr) (W_PCR), and glycolytic (W_[La^-]) systems were calculated during the combat simulation.

RESULTS

[La^-] increased significantly after NaHCO₃ ingestion, when compared with the placebo condition (+14%, P = 0.04, d = 3.70). NaHCO₃ ingestion resulted in greater estimated glycolytic energy contribution in the first round when compared with the placebo condition (+31%, P = 0.01, d = 3.48). Total attack time was significantly greater after NaHCO₃ when compared with placebo (+13%, P = 0.05, d = 1.15). W_OXI, W_PCR, VO₂, HR and RPE were not different between conditions (P > 0.05).

CONCLUSION

NaHCO₃ ingestion was able to increase the contribution of glycolytic metabolism and, therefore, improve performance during simulated taekwondo combat.

Sodium bicarbonate improves 4 km time trial cycling performance when individualised to time to peak blood bicarbonate in trained male cyclists

The aim of this study was to investigate the effects of sodium bicarbonate (NaHCO₃) on 4 km cycling time trial (TT) performance when individualised to a predetermined time to peak blood bicarbonate (HCO₃^-). Eleven male trained cyclists volunteered for this study (height 1.82 ± 0.80 m, body mass (BM) 86.4 ± 12.9 kg, age 32 ± 9 years, peak power output (PPO) 382 ± 22 W). Two trials were initially conducted to identify time to peak HCO₃^- following both 0.2 g^.kg^-1 BM (SBC2) and 0.3 g^.kg^-1 BM (SBC3) NaHCO₃. Thereafter, on three separate occasions using a randomised, double-blind, crossover design, participants completed a 4 km TT following ingestion of either SBC2, SBC3, or a taste-matched placebo (PLA) containing 0.07 g^.kg^-1 BM sodium chloride (NaCl) at the predetermined individual time to peak HCO₃^-. Both SBC2 (-8.3 ± 3.5 s; p < 0.001, d = 0.64) and SBC3 (-8.6 ± 5.4 s; p = 0.003, d = 0.66) reduced the time to complete the 4 km TT, with no difference between SBC conditions (mean difference = 0.2 ± 0.2 s; p = 0.87, d = 0.02). These findings suggest trained cyclists may benefit from individualising NaHCO₃ ingestion to time to peak HCO₃^- to enhance 4 km TT performance.