The use of ergogenic aids to improve performance is widespread (10,54,69), though their use is only recommended after a careful cost-benefit analysis (45). Alkalizing substances have been researched extensively for their potential to improve performance by minimizing the extent of metabolic acidosis, a contributor to fatigue during high-intensity exercise. One such agent that has attracted a wealth of attention is sodium bicarbonate (NaHCO3), which has been featured in the literature since as early as the 1930s (17) and regularly since the 1970s. The ingestion of NaHCO3 increases the level of bicarbonate (
) in the blood, a natural buffer that works by accepting a proton to form carbonic acid:
promotes a greater extracellular efflux of H+ and lactate, as demonstrated by a commonly reported higher blood lactate after exercise with NaHCO3 ingestion (74,86,95). Although there is a large body of evidence to support the use of NaHCO3 for sports performance, its use has been associated with possible gastrointestinal side effects (11). There is also conflicting research challenging its efficacy as an ergogenic aid, as highlighted in a number of review articles (9,52,65,71). Such reviews are essential because they summarize existing research and allow recommendations for evidence-based practice. However, the conclusions from review articles are susceptible to the opinions of the authors, because no statistical methods are used to support the arguments presented. A meta-analysis from almost 2 decades ago (43) reported only a moderate overall effect size (ES) for the effect of NaHCO3 on anaerobic performance. The analytical methods of this review allow a greater insight into the efficacy of NaHCO3 for sport performance; however, it was limited to the research of the time because there were few studies using trained subjects and no studies implementing prolonged protocols. There has since been a wealth of research articles on this topic, and therefore, a more up-to-date meta-analysis is needed to inform coaches, nutritionists, and athletes alike. The purpose of this study is to perform a meta-analysis to include more contemporary research. This will assist in the quantification of the efficacy of NaHCO3 ingestion for sports performance and provide practitioners a tool for the implementation of an effective cost-benefit analysis, that is, ergogenic potential vs. possible gastrointestinal distress.
A computer search for relevant peer-reviewed articles (excluding abstracts and unpublished theses and dissertations) was performed in January 2012 by entering various combinations of the following key words into PubMed, SPORTDiscus and Google Scholar; ‘sodium bicarbonate,’ ‘bicarbonate ingestion,’ ‘preexercise alkalosis,’ ‘ergogenic aids,’ ‘induced alkalosis,’ ‘acid-base balance,’ ‘sport nutrition,’ ‘sport performance,’ ‘sport,’ and ‘exercise.’ A manual cross-reference of relevant articles and review articles was also performed (9,52,65,71).
Inclusion Criteria and Excluded Studies
The retrieved articles were then selected for the meta-analysis according to the following inclusion criteria: (a) An acute dosage employed of 0.2–0.4 g·kg−1·body weight−1 60–120 minutes before exercise. This was chosen to take into account recommendations from recent research examining ingestion protocols (13,64,76). (b) Placebo-controlled, randomized, blinded, and repeated measures design. (c) Relevant raw data provided, that is, performance means and SDs. If the required raw data were not available in the article, then an attempt was made to contact the authors. (d) Human participants. (e) The main aim of the research was to examine the influence of NaHCO3 on performance. This was to assist clarity and allow recommendations to be made for performance. (f) Substance not combined with any other nutritional product and ergogenic aid.
All the studies that met these criteria are summarized in Table 1. The following studies were consequently excluded: (3,7,14,16–18,20,21,23–27,29,33–35,40,41,44,46,48,51,53,56,59,70,77,79,80,84,85,87,88,91,93,96) because they did not meet the inclusion criteria.
Coding and Classification of Variables
The articles selected that met the inclusion criteria were coded so as to categorize into the following characteristics: (a) Exercise type: Defined as either a single bout of exercise or a repeated bout exercise (e.g., repeated-sprints and sport-specific simulations). (b) Performance measure: Time to exhaustion, average and peak power, performance time, total work and distance completed and frequency of events. (c) Approximate exercise time: In studies employing a period of submaximal exercise before performance trial, only the performance aspect was counted. Recovery periods in repeated-sprint protocols were not included, and if a grand mean was calculated for repeated sprints, then the duration of 1 sprint and repetition was counted (see statistical analysis). (d) Training status of the participants: A trained participant refers to an athlete whose training plan is relevant for the respective exercise task, for example, Wilkes et al. (92) observing runners perform/compete in an 800-m race and Zabala et al. (94) observing BMX cyclists. Those participants described as healthy, active, and recreationally trained were classified as untrained. No sedentary participants were included. (e) Induced alkalosis: Calculated as the change in blood pH preingestion-postingestion in the experimental trial. To ensure consistency, only capillary blood results were analyzed because these were most common. (f) Induced acidosis: Calculated as the change in blood pH preexercise-postexercise in the placebo trial. To ensure consistency, only capillary blood results were analyzed because these were most common.
The effectiveness of the NaHCO3 supplementation was quantified by determining the ES for each variable, which can be categorized as small (0.2), moderate (0.5), or high (0.8). This was calculated using the following equation:
This equation was reversed in the case of those studies employing performance time as the performance measure, as a lower number would be considered beneficial. An ES for studies using repeated-sprint protocols was calculated from the total work/distance completed in all of the sprints. When these data were not available, a grand mean and pooled SD from the sprints was calculated. A weighted ES was then calculated to account for changes in individual sample sizes as described in Matson and Tran (43):
The effect of training status, ingestion type, and exercise type on the ES were analyzed using a Mann-Whitney U test, and exercise duration using the Kruskal-Wallis test as the analysis of Z-scores demonstrated an absence of normal distribution. Differences between performance measures were analyzed using a 1-way analysis of variance. Pearson correlation coefficients were used to analyze the nature and magnitude of relationships between variables. No statistics were employed when observing the differences between trained and untrained subjects in each performance measure and exercise duration category because of the varied data sets available.
There were 40 research articles that met the inclusion criteria for the meta-analysis, allowing the analysis of 58 ESs from 395 participants (348 men and 47 women). Of the articles included, 15 (38%) reported an ergogenic benefit. A tracking of positive and no effect publications by year is presented in Figure 1, with only those studies selected for inclusion in the meta-analysis shown to allow comparison within similar ingestion protocols. The summary of all the ESs is available in Table 2. The overall ES for the influence of NaHCO3 on performance regardless of performance measure, duration, and training status was 0.41 (weighted mean = 0.36). The overall ES was significantly higher in untrained participants compared with trained participants (p = 0.007), and higher in single bout as opposed to repeated bout exercises (p = 0.013). The ES was higher in studies administering NaHCO3 as a liquid solution as opposed to capsules but not significantly so (p = 0.457).
Exercise protocols employing a time to exhaustion or total work performance measure resulted in a much higher ES than the overall ES (0.60 and 0.63, respectively). The time to exhaustion ES however was lowered when the weighted mean is observed (0.50). In contrast, those studies using performance time or power as a performance measure resulted in much lower ESs of 0.17 and 0.27, respectively, with performance time reducing to 0.09 after weighting. Despite this, there were no significant differences in ESs between performance measures (F = 2.03, p = 0.12). None of the differences between exercise duration were significant (p = 0.501).
There was a moderate but significant overall relationship between ES and the state of induced alkalosis (n = 27, r = 0.45, p = 0.02), and this relationship was stronger in trained than in untrained participants (n = 15, r = 0.56, p = 0.03 and n = 12, r = 0.50, p = 0.10, respectively). The overall relationship between ES and the state of induced acidosis was weak and insignificant (n = 24, r = 0.25, p = 0.237).
A moderate overall weighted ES for the impact of NaHCO3 on performance was calculated (0.36), lower than that reported by Matson and Tran in 1993 (0.44). This is possibly because of the increased number of publications challenging its efficacy as an ergogenic aid in recent years (Figure 1). Another explanation for this may be the greater number of trained participants in this review as a significantly lower ES was observed for this group. This finding is in contrast to previous opinion, with Webster et al. (89) claiming that the use of trained subjects was a factor consistently associated with improved performance with NaHCO3. Requena et al. (65) supported this suggestion claiming that more highly trained subjects have a higher maximal rate of anaerobic glycolysis, allowing alkaline treatment to have a more significant effect. It may instead be the case that training adaptations such as increased density of monocarboxylate transporter proteins (31) and improved muscle buffering capacity (19,90) are more effective than NaHCO3 administration for trained athletes, whereas their lesser trained counterparts are more reliant on the extra buffering capacity afforded by the NaHCO3. This is supported by the relationship observed between induced alkalosis and ES, as the correlation was statistically significant in trained but not untrained participants, suggesting that only greater inductions of alkalosis has the potential to influence performance in trained individuals as Zabala et al. suggested recently (94). It must be considered that these relationships are limited to the studies included in the meta-analysis and of capillary blood and also that a significant correlation does not represent causation.
A number of research articles have reported ergogenic effects for NaHCO3 when using repeated-sprint exercises, however, not until after the first (37) or second repetition (1,6,88). These studies suggest that a single bout exercise is unlikely to benefit from NaHCO3 administration, because its benefit arises from the improvement in acid-base recovery allowed between bouts (74). However, this study found a statistically higher performance ES in single bout as opposed to repeated bout exercises. It must be considered though that there are different proportions of trained to untrained participants in these categories, and ESs are similar when only taking into account trained participants.
The overall ES was higher in studies employing time to exhaustion or total work completed as a performance measure rather than performance time or power. However, the time to exhaustion and total work groups had a high proportion of untrained subjects, whereas the performance time group had a high proportion of trained subjects (only 1 untrained ES in group), therefore influencing the overall ESs. It is interesting that trained subjects in the performance time group had one of the lowest ESs, because it could be argued that this combination would be most applicable to elite sporting performance. Despite the differences between performance measures, there were no statistically significant differences in overall ESs. The absence of statistical differences between performance measures could be because of the differences in the size of the data sets between groups, coupled with the large confidence intervals, which often resulted in negative values at the lower 95% limit.
The most common duration of exercise protocols used to investigate the use of NaHCO3 was up to approximately 120 seconds (Table 2). This is presumable because high-intensity efforts of this duration are predominantly associated with anaerobic glycolysis. However, the overall ES for this duration of exercise was no different to medium (2–10 minutes) and long (>10-minute) duration protocols. Within the short duration category, the ES is much higher in untrained than in trained subjects, again suggesting that untrained subjects are more reliant on the extra buffering potential afforded by NaHCO3. However, once more, the confidence intervals must be taken into consideration. The similar overall ESs across exercise durations may suggest that the extra buffering capacity is not the sole mechanism behind its potential effect on performance. There has been some work to suggest that NaHCO3 may improve perceptual responses to exercise, which could account for the similarly moderate ES for longer exercise protocols (67,81,82). However, as with most research regarding NaHCO3, there is also a wealth of evidence on the contrary (1,60,78,93,95).
It should be considered when interpreting our findings that although the NaHCO3 dosages were similar in the observed studies, the method of administration differed. The majority of the studies administered the buffer in liquid solutions including water, flavored water, fruit juice and soup, whereas the other method used capsules. We have anecdotal evidence from our laboratory and others (94) that some side effects are induced by the taste of NaHCO3 in a liquid solution and that it is easier to tell the difference between placebo and NaHCO3 when ingested in a liquid solution as opposed to capsules. This is problematic for research design because there is a strong placebo effect associated with this particular buffer (47). The mean ES reported in this study is higher in those studies administering NaHCO3 in solution compare to capsules (0.46 and 0.32, respectively), particularly when observing the weighted mean (0.41 and 0.25, respectively) (Table 2). However, it must be added that there were no significant differences between said ESs. Future work should not only compare the incidence and severity of side effects between ingesting NaHCO3 in solution and capsules (as recently done by Carr et al. ) but also any potential differences in athletic performance.
The ergogenic potential of NaHCO3 had an overall moderate ES and appeared to be more effective in recreationally as opposed to specifically trained participants. This ES however was highly variable when considering the 95% confidence intervals. Coaches and athletes can take the following practical applications from the results of this review: (a) The use of NaHCO3 should be made on an individual basis as although negative ESs were in the minority (Table 1), a number of the ESs had negative lower confidence intervals (Table 2), meaning a potentially adverse performance effect in some athletes. (b) Care should be taken when evaluating results from studies using performance measures and participants unrelated to their field. (c) The combination of trained participants and performance time resulted in a very weak weighted ES (0.05). (d) Potential performance improvements may not be limited to short exercise protocols. (e) Although it appears that only minor benefits are afforded to trained individuals, such small margins may be significant at the elite level. If NaHCO3 is to be used then it is suggested to experiment with loading protocols to develop an individual specific routine to achieve a peak alkalosis and minimize the risk of potential side effects (13). A recommended starting dosage is 0.2–0.4 g·kg−1·body weight−1 and 60–120 minutes preexercise in flavored water or capsules.
Future research should focus where possible on trained subjects performing sport-specific tasks, such as those studies on boxing (73), water polo (83), rugby (11), judo (1), and BMX cycling (94,95). Such research would avoid inflating the efficacy of NaHCO3 with untrained subjects who are unlikely to use it and so allow coaches, nutritionists, and athletes to make more informed decisions about their respective sport.
The authors wish to thank all those authors who provided us with missing data not available in their published articles.
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