Effect of acute sodium bicarbonate ingestion on excess CO2 output during incremental exercise

The effect of sodium bicarbonate mini-tablets ingested in a carbohydrate hydrogel system on 40 km cycling time trial performance and metabolism in trained male cyclists

INTRODUCTION

Sodium bicarbonate (NaHCO3) ingestion has been found to be ergogenic in high-intensity exercise that ranges from 1 to 10 min; however, limited studies have investigated high-intensity exercise beyond this duration.

PURPOSE

The present study aimed to determine the effect of NaHCO3 ingested using a carbohydrate hydrogel delivery system on 40 km time trial (TT) performance in trained male cyclists.

METHODS

Fourteen trained male cyclists ingested 0.3 g kg-1 BM NaHCO3 (Maurten AB, Sweden) to determine individualised peak alkalosis, which established time of ingestion prior to exercise. Participants completed a 40 km familiarisation TT, and two 40 km experimental TTs after ingestion of either NaHCO3 or placebo in a randomised, double-blind, crossover design.

RESULTS

NaHCO3 supplementation improved performance (mean improvement = 54.14 s ± 18.16 s; p = 0.002, g = 0.22) and increased blood buffering capacity prior to (HCO3- mean increase = 5.6 ± 0.2 mmol L-1, p < 0.001) and throughout exercise (f = 84.82, p < 0.001, pη2 = 0.87) compared to placebo. There were no differences in total gastrointestinal symptoms (GIS) between conditions either pre- (NaHCO3, 22 AU; Placebo, 44 AU; p = 0.088, r = 0.46) or post-exercise (NaHCO3, 76 AU; Placebo, 63 AU; p = 0.606, r = 0.14).

CONCLUSION

The present study suggests that ingesting NaHCO3 mini-tablets in a carbohydrate hydrogel can enhance 40 km TT performance in trained male cyclists, with minimal GIS. This ingestion strategy could therefore be considered by cyclists looking for a performance enhancing ergogenic aid.

Sodium bicarbonate improves sprint performance in endurance cycling

OBJECTIVES

Oral sodium bicarbonate intake (NaHCO₃) may improve performance in short maximal exercise by inducing metabolic alkalosis. However, it remains unknown whether NaHCO₃ also enhances all-out performance at the end of an endurance competition. Therefore, the present study investigated the effect of stacked NaHCO₃ loading on sprint performance following a 3-h simulated cycling race.

DESIGN

Double-blind randomized placebo-controlled cross-over study.

METHODS

Eleven trained male cyclists (22.3 (18.3-25.3) year; 73.0 (61.5-88) kg; VO₂max: 63.7 (57-72) mlkg^-1min^-1) ingested either 300mgkg^-1 body weight NaHCO₃ (BIC) or NaCl (PL). NaHCO₃ or NaCl was supplemented prior to (150mgkg^-1) and during (150mgkg^-1) a 3-h simulated cycling race with a 90-s all-out sprint (90S) at the end. Capillary blood samples were collected for determination of blood pH, lactate and HCO₃^- concentrations. Analysis of variance (lactate, pH, HCO₃^-) and paired t-test (power) were applied to compare variables across condition (and time).

RESULTS

NaHCO₃ intake improved mean power during 90S by ∼3% (541±59W vs. 524±57W in PL, p=0.047, Cohen's D=0.28, medium). Peak blood lactate concentration and heart rate at the end of 90S were higher (p<0.05) in BIC (16.2±4.1mmoll¹, 184±7bpm) than in PL (12.4±4.2mmoll^-1, 181±5bpm). NaHCO₃ ingestion increased blood [HCO₃^-] (31.5±1.3 vs. 24.4±1.5mmoll^-1 in PL, p<0.001) and blood pH (7.50±0.01 vs. 7.41±0.03 in PL, p<0.05) prior to 90S.

CONCLUSIONS

NaHCO₃ supplementation prior and during endurance exercise improves short all-out exercise performance at the end of the event. Therefore, sodium bicarbonate intake can be applied as a strategy to increase success rate in endurance competitions.

Physiological responses and energy cost during a simulation of a Muay Thai boxing match

Muay Thai is a martial art that requires complex skills and tactical excellence for success. However, the energy demand during a Muay Thai competition has never been studied. This study was devised to obtain an understanding of the physiological capacities underlying Muay Thai performance. To that end, the aerobic energy expenditure and the recruitment of anaerobic metabolism were assessed in 10 male athletes during a simulation match of Muay Thai. Subjects were studied while wearing a portable gas analyzer, which was able to provide data on oxygen uptake, carbon dioxide production, and heart rate (HR). The excess of CO2 production (CO2 excess) was also measured to obtain an index of anaerobic glycolysis. During the match, group energy expenditure was, on average (mean ± standard error of the mean), 10.75 ± 1.58 kcal·min–1, corresponding to 9.39 ± 1.38 metabolic equivalents. Oxygen uptake and HRs were always above the level of the anaerobic threshold assessed in a preliminary incremental test. CO2 excess showed an abrupt increase in the first round, and reached a value of 636 ± 66.5 mL·min–1. This parameter then gradually decreased throughout the simulation match. These data suggest that Muay Thai is a physically demanding activity with great involvement of both the aerobic metabolism and anaerobic glycolysis. In particular, it appears that, after an initial burst of anaerobic glycolysis, there was a progressive increase in the aerobic energy supply. Thus, training protocols should include exercises that train both aerobic and anaerobic energetic pathways.

Bicarbonate infusion and pH clamp moderately reduce hyperventilation during ramp exercise in humans

To test the hypothesis that the decrease in plasma pH contributes to the hyperventilation observed in humans in response to exercise at high workloads, five healthy male subjects performed a ramp exercise [maximal workload: 352 W (SD 35)] in a control situation and when arterialized plasma pH was maintained at the resting level (pH clamp) by intravenous infusion of sodium bicarbonate [129 mmol (SD 23), beginning at 59% maximal workload (SD 5)]. Bicarbonate infusion did not modify O(2) consumption (Vo(2)) but significantly (P < 0.05) increased arterial Pco(2), plasma bicarbonate concentration, and respiratory exchange ratio (P < 0.05). At the three highest workloads, pulmonary ventilation (Ve) and Ve/Vo(2) were approximately 5-10% lower (P < 0.05) when bicarbonate was infused than in the control situation, and hyperventilation was reduced by 15-30%. These data suggest that the decrease in plasma pH is one of the factors that contribute to the hyperventilation observed at high workloads.

Model for the behaviour of compartmental CO(2) stores during incremental exercise

The respiratory exchange ratio (RER) is a valid method for determining fat and carbohydrate oxidation during exercise when the exchange of respiratory gas is in a state of steady flux between the tissue and fluid compartments and the alveoli. However, under incremental intensity or heavy exercise conditions, the movement of electrolytes, fluids, and CO(2) between body-fluid compartments is accentuated, leading to increased hydrogen-ion concentration ([H(+)]), decreased bicarbonate-ion concentration ([HCO(3) (-)]) and CO(2) stores, and the excretion of additional CO(2) at the alveoli (i.e. H(+)+HCO(3) (-) --> CO(2)+H(2)O) elevating the CO(2) minute volume. This non-respiratory CO(2) excretion can invalidate use of the RER for determination of fat and carbohydrate oxidation. Direct measurement of the labile CO(2) store and non-respiratory CO(2) excretion during exercise is difficult. Therefore, physicochemical models were derived to illustrate the likely behaviour of compartmental CO(2) stores during 8 W.min(-1) incremental cycling exercise to formulate correction factors to the RER for the non-respiratory CO(2) component. From these models, a polynomial regression equation was derived to describe the change in the total labile CO(2) store volume during incremental exercise from the relationship with blood HCO(3) (-) content: CO(2) volume (ml) = -17x(2)+464x+650, where x is the arterialised blood standard HCO(3) (-) concentration (mmol.l(-1)), relative to resting conditions. Non-respiratory CO(2) excretion (ml.min(-1)) was then determined from the rate of change in CO(2) volume. The modelling method could allow for straightforward calculation of the non-respiratory CO(2) excretion rate for future validation work.

Metabolic effects of induced alkalosis during progressive forearm exercise to fatigue

Metabolic alkalosis induced by sodium bicarbonate (NaHCO3) ingestion has been shown to enhance performance during brief high-intensity exercise. The mechanisms associated with this increase in performance may include increased muscle phosphocreatine (PCr) breakdown, muscle glycogen utilization, and plasma lactate (Lac-pl) accumulation. Together, these changes would imply a shift toward a greater contribution of anaerobic energy production, but this statement has been subject to debate. In the present study, subjects ( n = 6) performed a progressive wrist flexion exercise to volitional fatigue (0.5 Hz, 14–21 min) in a control condition (Con) and after an oral dose of NaHCO3 (Alk: 0.3 g/kg; 1.5 h before testing) to evaluate muscle metabolism over a complete range of exercise intensities. Phosphorus-31 magnetic resonance spectroscopy was used to continuously monitor intracellular pH, [PCr], [Pi], and [ATP] (brackets denote concentration). Blood samples drawn from a deep arm vein were analyzed with a blood gas-electrolyte analyzer to measure plasma pH, Pco2, and [Lac-]pl, and plasma [Formula: see text] was calculated from pH and Pco2. NaHCO3 ingestion resulted in an increased ( P < 0.05) plasma pH and [Formula: see text] throughout rest and exercise. Time to fatigue and peak power output were increased ( P < 0.05) by ∼12% in Alk. During exercise, a delayed ( P < 0.05) onset of intracellular acidosis (1.17 ± 0.26 vs. 1.28 ± 0.22 W, Con vs. Alk) and a delayed ( P < 0.05) onset of rapid increases in the [Pi]-to-[PCr] ratio (1.21 ± 0.30 vs. 1.30 ± 0.30 W) were observed in Alk. No differences in total [H+], [Pi], or [Lac-]pl accumulation were detected. In conclusion, NaHCO3 ingestion was shown to increase plasma pH at rest, which resulted in a delayed onset of intracellular acidification during incremental exercise. Conversely, NaHCO3 was not associated with increased [Lac-]pl accumulation or PCr breakdown.

Physiological model of CO2 output during incremental exercise

In this study, a physiological model to explain the pathway of CO2 output during incremental exercise was examined by referring to experimental data. Since CO2 output (VCO2) shows multiple correlations with mixed venous CO2 pressure (PvCO2) and arterial CO2 pressure (PaCO2), the increase in the difference between PvCO2 and PaCO2 was considered to be involved in the increase in VCO2. In order to better understand the influence of CO2 pressure, VCO2 was divided into the expiratory CO2 phase (non-lactic VCO2), which was unrelated to lactic acid increase and the expiratory CO2 phase (excess VCO2), which was related to lactic acid increase. As a result, the non-lactic VCO2 significantly correlated to PvCO2. When non-lactic VCO2 was zero, the value of PvCO2 was 43.7 mmHg. This was higher than the resting PaCO2 value. On the other hand, as PaCO2 showed an almost constant value in the low load phase and showed a low value in the high load phase, it was believed that the low value of PaCO2 was related to the excess VCO2 that appeared in the high load phase. The CO2 excess, which was obtained by adding excess VCO2 in terms of the lapse of exercise time, correlated significantly with an increase in lactate in the blood. Based on the results, a model was constructed to illustrate the pathway of CO2 output. The key points of the model were as follows: (1) the use of the blood CO2 dissociation curve as the vector to transport CO2 from tissue to lungs, (2) the standard value of PaCO2 was established in order to divide non-lactic VCO2 and excess VCO2, (3) the dextroversion of the blood CO2 dissociation curve due to lactic acid was connected to excess VCO2, and (4) a decrease in PaCO2 was related to excess VCO2 derived from tissue.

Prediction of blood lactate accumulation from excess CO2 output during constant exercise

To determine the predictability of blood lactate accumulation from excess CO2 output derived from bicarbonate buffering of lactic acid during constant exercise, eight normal active volunteers were studied during three stages of constant exercise on a cycle ergometer. Three work rates consisted of 100% (stage I), 120% (stage II) and 150% (stage III) of each subject's anaerobic threshold (AT), each of which was lasted for 4 min. Excess CO2 output (Ex CO2, ml) at each stage of constant exercise was estimated form the integral of difference between total VCO2 and aerobic VCO2 (from regression line for VCO2 and VO2 at exercise intensities below the AT obtained in incremental exercise test). Ex CO2 per body mass (Ex CO2-mass-1) was increased progressively with blood lactate (La) accumulation from rest to each stage of constant exercise. Mean values (+/-SD) in the measured La accumulation (delta La,measured) and predicted La accumulation (delta La,predicted) at three stages of constant exercise were 1.82 +/- 0.83 vs 3.19 +/- 1.70 for stage 1, 5.58 +/- 3.47 vs 7.09 +/- 3.28 for stage II and 12.19 +/- 2.36 vs 12.74 +/- 1.83 mmol.l-1 for stage III, respectively. There was a significant difference between delta La,measured and delta La,predicted at stage I (p < 0.05), but no significant differences between these two variables at stage II and III. The averaged difference from delta La,predicted to delta La,measured at stage III (0.55 mmol.l-1) showed a tendency to be smaller than stage I (1.38 mmol.l-1) and II (1.50 mmol.l-1). On the other hand, delta La,predicted was found to correlate very closely with delta La,measured (r = 0.954, P < 0.001, n = 20). The results of this study suggest that the changes of La accumulation could be predicted from excess CO2 output generated in constant exercises above the AT.