During high-intensity exercise, the muscles mainly supplies energy through anaerobic metabolism to meet the energy demand (Gastin, 2001). In this process, it is inevitable to produce some metabolic acidic substances, such as lactate. The muscle lactate will cross the muscle cell membrane and enter the blood through diffusion or transfer. If the lactate cannot be removed in time, it will be decomposed into lactate and H⁺, resulting in H⁺ accumulation (Zinner et al., 2011). The increase of H⁺ will lead to an imbalance of acid-base balance and hinder the production of ATP (Juel, 2001), which will damage the contractile ability of muscles and ultimately affect exercise ability and performance. Therefore, it is very necessary to take reasonable measures to promote muscle acid-base balance during exercise.

Regulating the acid-base balance through nutrition is one of the important methods to alleviate fatigue and promote physical recovery (Naderi et al., 2016) quickly. During the past decades, numerous studies have demonstrated that increases in the extracellular buffer concentration via the oral ingestion of an alkaline solution, such as sodium bicarbonate may enhance human exercise performance (Wilkes et al., 1983; McNaughton et al., 1999; Requena et al., 2005; Lindh et al., 2008; Zabala et al., 2008; Ferreira et al., 2019). Sodium bicarbonate ingestion leads to an increase in plasma bicarbonate (HCO₃ ⁻) concentration. The increase in extracellular pH leads to a greater transmembrane H+ concentration gradient, stimulating the co-transport of H+ and lactate from the exercising muscle cell. It has also been established that ingestion of Na⁺ can increase the plasma volume (Greenleaf and Brock, 1980), which could also benefit anaerobic activity by creating an enlarged buffering potential through dilution of the H⁺ concentration. Other studies have identified that acute or chronic exogenous HCO₃ ⁻ may improve performance in 400 m races, high-intensity cycling, the Wingate test, and other anaerobic activities (Pouzash et al., 2012; Saunders et al., 2014; Dalle et al., 2021). Previous studies on the effect of sodium bicarbonate on anaerobic capacity were fewer. One study explored different levels of sodium bicarbonate intake that influenced acid-base balance and performance during high-intensity exercise (DouroudosFatouros et al., 2006), and another study examined the effect of sodium bicarbonate ingestion on performance and perceptual responses (Zabala et al., 2008).

Based on a comprehensive review of the international Society of Sports Nutrition position on sodium bicarbonate and exercise performance, the ergogenic effects of sodium bicarbonate are mostly established for exercise tasks of high-intensity that last between 30 s and 12 min (Driller et al., 2012; Mündel, 2018; Grgic et al., 2021; Grgic, 2022). The Wingate test is a common method to evaluate anaerobic exercise performance and has been used more often in studies related to sodium bicarbonate. However, the results of exploring the performance of sodium bicarbonate on the Wingate test were found to be ambiguous (Zabala et al., 2008; Zabala et al., 2011; Saunders et al., 2014). Based on previous literature (Zinner et al., 2011), the present study adapted the exercise protocol and used four Wingate anaerobic 30s cycling tests as the exercise protocol. Sodium bicarbonate supplementation (doses from 0.2 to 0.5 g/kg) may improve the performance of muscular endurance activities. Although 0.2 g/kg of sodium bicarbonate appears to be the minimum dose needed to improve exercise performance, there are still findings of gastrointestinal discomfort at this dose (Gough et al., 2017). Based on the literature and pre-experimental results, an intake dose of 0.2 g/kg was used in this study.

Sodium bicarbonate supplementation has the possibility of gastrointestinal discomfort, resulting in symptoms such as nausea, stomach pain, diarrhea, and vomiting (Burke and Pyne, 2007). One study also discovered that abdominal distress was significantly more prominent in the sodium bicarbonate trial than the placebo, resulting in an increase in stomach cramping, stomach ache, and diarrhea in the participants immediately after consumption. A larger increase in symptoms may have impacted performance (Miller et al., 2016). By applying a novel ingestion strategy to an enteric coating (containing hydroxypropyl methylcellulose, shellac, etc.), it resists dissolution in the gastric acid environment, and acid-sensitive components such as sodium bicarbonate can bypass the gastric (Barbosa et al., 2017). Since GI distress during sodium bicarbonate application may be partly attributable to degradation in the stomach (Turnberg et al., 1970), enteric coating can reduce the neutralizing effect of gastric acid and largely reduce side effects. Some studies have reported that enteric-coated sodium bicarbonate can attenuate gastrointestinal symptoms following acute bicarbonate loading on aerobic exercise performance have been investigated (Hilton et al., 2020). Evidence suggests that athletes may be deterred from supplementing with sodium bicarbonate due to the risk of GI symptoms during training or competition (Heibel et al., 2018). However, fewer studies have been conducted on the effects of acute enteric-coated sodium bicarbonate supplementation on the physiological profile, anaerobic performance, and symptoms of gastrointestinal discomfort.

Metabolomics is a new approach after genomics, proteomics, and transcriptomics with the advantages of high throughput, high specificity, and high sensitivity. Metabolomics is routinely applied as a tool for biomarker discovery to understand the systems-level effects of metabolites (Johnson et al., 2016). It is the profiling of metabolites in biofluids, cells, and tissues. The use of urine provides an ideal non-invasive method that results in a large overview of the metabolite matrix (Daskalaki et al., 2015). With the recent emergence of metabolomics analyses, metabolomics is now being applied to choosing exercise and nutritional supplements (Nieman et al., 2015; Al-Khelaifi et al., 2018). Metabolomics analysis can be either targeted (that focused on quantitative measurements of usually small numbers of metabolites) or untargeted (that focused on metabolic profiling of the total complement of metabolites for the studied samples) (Emwas et al., 2021). Targeted metabolomics focuses on analyzing several selected metabolites, such as studies related to specific metabolic pathways, drug toxicology, and specific effects of certain foods/nutrients. However, metabolomics analysis methods are less applied in the study of enteric-coated sodium bicarbonate.

Some studies have examined sodium bicarbonate supplementation during high-intensity exercise affects performance. However, the findings are equivocal, and some studies did not find significant differences between sodium bicarbonate and placebo conditions (Joyce et al., 2012; Driller et al., 2013). The researchers hypothesized that the finding may have been due to the unique subject characteristics (highly trained members of national teams) (Edge et al., 2004; Carr et al., 2011; Wang et al., 2019). Based on these findings, healthy college students were chosen to be the participants of this study instead of highly trained athletes, to better understand the possible impact of sodium bicarbonate ingestion when coupled with high-intensity exercise.

The results of past studies led us to develop a research project that would investigate the effects of acute enteric-coated sodium bicarbonate supplementation on anaerobic performance, heart rate, blood lactate, and symptoms of gastrointestinal discomfort in healthy young men. The target metabolomics based on the multi-reaction monitoring technology (MRM) method was used to analyze the specific metabolic pathway. It was hypothesized that both supplementation conditions would improve anaerobic performance. However, enteric-coated sodium bicarbonate was more effective in reducing the incidence of gastrointestinal side effects.

Data were entered into Microsoft Excel 2010 and analyzed with SPSS 26.0. Data were analyzed using parametric tests following confirmation of a normal distribution via the Shapiro-Wilks-W-test and are presented as mean ± standard deviation (SD). Normally distributed data sets were analyzed with appropriate parametric statistical tests. Repeated-measures ANOVA compared conditions for significant differences among the three trials (MP, PP, BLA, HR, and RPE). Simple effect analysis was performed for the horizontal comparison of between-group factors when there was an interaction, and longitudinal comparison of within-group factors was performed when there was no interaction. In order to evaluate differences following the ingestion of GS and ES, effect sizes were calculated for each variable. In all cases, the significance level was set at P < 0.05. In addition, urine sample data was extracted by Multiquant software for peak area and retention time. The retention time was corrected using standards of energy metabolites for metabolite identification.

The main findings of this analysis were that, compared to PL, acute ingestion of ES and GS did not significantly improve either peak power or mean power during the WACT, regardless of the number of tests performed. However, compared to placebo, the intake of ES and GS increased the values of peak and mean power during the third and fourth WACTs (Figure 2). In addition, some additional changes occurred in ES and GS, including a decrease in the average power drop range. Our data suggest that in the population studied, enteric-coated and general sodium bicarbonate may have some positive impact on the Wingate tests on anaerobic capacity. One possible explanation for this finding is that power is more related to glycolytic metabolism and is limited by H⁺ accumulation (Lancha Junior et al., 2015; Lopes-Silva et al., 2019). Therefore, the buffering action of sodium bicarbonate could be more effective at minimizing fatigue and increasing mean power during the test, particularly in later stages (Lopes-Silva et al., 2019). Based on the literature reviewed, the failure of alkalosis to increase Wingate performance may be explained by an insufficient time during the exercise to allow a significant difference in H⁺ ion efflux from the muscle fibers or an inability to generate a sufficient difference in H⁺ ion gradient to produce a difference between trials (Mainwood and Worsley-Brown, 1975; Linderman and Fahey, 1991; Marx et al., 2002; Forbes et al., 2005; Street et al., 2005). Overall, these results suggest that sodium bicarbonate may have an ergogenic effect on repeated WACT test performance (Grgic, 2022). The likely explanation is also that recovery between bouts of exercise is enhanced by enhanced buffering capacity. However, one study has also suggested that sodium bicarbonate ingestion results in significant shifts in the acid-base balance of the blood and has a small but non-significant effect on anaerobic power and capacity (Parry-Billings and MacLaren, 1986). Our data are similar to the results of the study, but there is no significant change. This may be due to the higher intake dose in these studies than in the study we designed, although our dose is also effective in some studies (Durkalec-Michalski et al., 2020).

The findings demonstrated that BLA was not significantly different among experimental conditions in all tests. From the overall trend, the BLA of participants in enteric-coated and general sodium bicarbonate decreased more rapidly during the decline of BLA. We speculated that enteric-coated and general sodium bicarbonate might promote lactate clearance after exercise, reducing lactate accumulation. Some studies have indicated that sodium bicarbonate can change the content of blood lactate (Hartono and Sukadiono, 2017; Rezaei et al., 2019). Evidence suggests that sodium bicarbonate promotes non-oxidative energy metabolism, as observed through greater muscle lactate production and muscle glycogen utilization during intermittent exercise performed in the severe-intensity domain (Percival et al., 2015). However, if lactate is not removed in time, it will be decomposed and converted into lactate and cause a large amount of H⁺ accumulation, resulting in muscle acidification, causing acidosis (Zinner et al., 2011). The increase in buffering capacity achieved by ingesting sodium bicarbonate before exercise has previously been well documented (Siegler et al., 2010). Although our data suggest no significant difference among three conditions in the BLA (p > 0.05), the supplementation of enteric-coated and general sodium bicarbonate positively impacted the lactate clearance trend after exercise.

Three participants experienced serious problematic GI effects during our three experiments after taking general sodium bicarbonate and failed to complete the entire experiment. Previous studies have suggested that general sodium bicarbonate can adversely affect GI comfort (Cameron et al., 2010; Carr et al., 2011; Saunders et al., 2014). The accumulation of CO₂ in the stomach, resulting from supplementation with sodium bicarbonate, may cause bloating, nausea, vomiting, and abdominal pain (Kahle et al., 2013). The incidence and severity of these side-effects increase linearly with the dose of sodium bicarbonate ingested and should be considered in terms of their overall effect on performance (Cameron et al., 2010). In this study, gastrointestinal discomfort was shown to be significantly more prominent in the general sodium bicarbonate trial than the placebo and enteric-coated sodium bicarbonate, resulting in an increase in stomach cramping, stomach ache, and diarrhea in the participants in sports. There was a larger increase in symptoms that may have impacted on performance. Therefore, following general sodium bicarbonate supplementation, these side effects may negatively impact exercise performance. More recent evidence suggests that enteric-coated sodium bicarbonate is a possible strategy to minimize the likelihood and severity of these side effects (Hilton et al., 2020). Our results support this study.

At baseline, no differences were observed among the three trials for HR. As expected, exercise resulted in increases in HR; all measures returned toward baseline during recovery from exercise (Table 2). This is similar to the study suggesting no improvement in heart rate recovery after exercise following sodium bicarbonate supplementation (Wang et al., 2019).

Based on RPE data, ES or GS did not affect RPE during a series of WACTs. This result disagrees with those published previously (Swank and Robertson, 1989; Swank and Robertson, 2002) showing lower RPEs under alkalotic conditions relative to placebo. Similar results have been demonstrated in the other study, showing that RPE measured immediately after each WACT was not affected by sodium bicarbonate ingestion (Zabala et al., 2008). This may be due to the excessive exercise intensity and short intervals during each WACT, resulting in little subjective feeling.

The targeted metabolomics tests cover important metabolites in the tricarboxylic acid cycle, glycolytic, and oxidative phosphorylation processes (see Figure 8). The metabolites of the participants in the three conditions were found to be diverse at that time. Studies have demonstrated that due to the high intensity and short movement duration, it is characterized by an energy supply derived primarily from glycolytic metabolism. In the ES, excluding citrate, the levels of 3-phospho-d-glycerate, pyruvate, cis-aconitate, and oxaloacetate were increased 50 min after exercise compared with the levels of exercise in the PL and GS, while d-Glucose 6-phosphate decreased. d-Glucose 6-phosphate, 3-phospho-d-glycerate, and pyruvate are the intermediate products of glucose catabolism. Glucose is the main energy-supplying substance in humans. ES more potently induced circulating glucose metabolism and the TCA cycle than GS and PL. It appears that both greater muscle buffering capacity and enhanced removal of protons result in increased glycolytic ATP production (Chycki et al., 2018). Citrate, oxaloacetate, and cis-aconitate are the intermediate products of the TCA cycle. The tricarboxylic acid cycle (TAC) is a necessary metabolic pathway in tissue energy supply and is distributed in the mitochondria. From the results, it is clear that the ES and GS affect the metabolic substances of the TAC metabolic pathway. Compared with the PL, an increase in intermediates of the TCA cycle was observed in the ES, including cis-aconitate, oxaloacetate, and citrate. It is hypothesized that the increased amount of TCA circulating intermediate in the blood may be due to the positive effect of ES intake on acidic substances clearance, which can promote the production of more energy in mitochondria for consumption by the system. The results showed that the differential metabolites related to the tricarboxylic acid cycle, aconitate and oxaloacetate decreased significantly, and citrate increased significantly, indicating the disorder of the tricarboxylic acid cycle. It may be due to side effects affecting the state of the exercise.

Lactate is a metabolite produced by the anaerobic enzymatic supply of glycogen and glucose outside the mitochondria in a state of oxygen deprivation. Various studies have confirmed that sodium bicarbonate increases extracellular pH and promotes H⁺ and lactate efflux from active muscles (Driller et al., 2012; Rezaei et al., 2019). The level of lactate in the ES of the pro-test was higher than that in the PL. It is hypothesized that ES supplementation promotes lactate clearance.

There are some limitations to the current study. Our study employed a limited sample of solely healthy young males, limiting its generalizability to other demographics. Coaches and athletes may consider using these supplements to give a possible performance edge, taking into personal account response.

Based on these results, it was concluded that acute enteric-coated sodium bicarbonate and general sodium bicarbonate do not improve anaerobic exercise performance. Based on the analysis of target metabolomics, enteric-coated sodium bicarbonate and general sodium bicarbonate supplementation can affect the metabolism of substances, including 3-phospho-d-glycerate, d-Glucose 6-phosphate, pyruvate, cis-aconitate, oxaloacetate, citrate, and lactate. In healthy young men, the supplementation of acute enteric-coated sodium bicarbonate and general sodium bicarbonate can enhance some of the weak effects of blood lactate clearance during anaerobic exercise, which may be beneficial for glycolytic energy supply. An important point to note is that general sodium bicarbonate is a serious gastrointestinal problem, while enteric-coated sodium bicarbonate supplements can relieve gastrointestinal distress.