It is known that the capacity of skeletal muscle to maintain energy exchange and generate mechanical work is related to sports performance in a wide variety of sports. That is why an increase in the energy turnover of ATP (the energy currency used by our body) during short-duration, high-intensity efforts is related to glycolytic metabolism and the increase of hydrogen ions (H+) triggering what is called muscle acidosis along with a loss in performance.
Exercise-induced metabolic acidosis occurs when H+ production exceeds its removal rate. This reduces energy production through glycolytic pathways by decreasing the activity of key enzymes such as glycogen phosphorylase and phosphofructokinase.
H+ ions also compete with calcium ions for the binding site on troponin, which directly hinders the ability of skeletal muscle to contract. Meanwhile, other bioenergetic processes such as oxidative phosphorylation and phosphocreatine resynthesis can also be compromised at a low pH. Therefore, a drop in muscle pH leads to an inability to produce the desired or required power, with a subsequent loss of exercise performance.
That is why our body has several endogenous systems to control pH homeostasis; this balance is maintained through intracellular and extracellular buffers that can accept or release H+ to prevent drastic changes in pH.
In the muscle, physicochemical buffers, such as organic and inorganic phosphates, bicarbonate anions, and dipeptides like carnosine (histidine + beta-alanine) are the main mediators of pH homeostasis. The main problem is that these buffers are extremely efficient under physiological conditions; however, during high-intensity exercise they can be compromised by excess H+.
This post examines practical considerations for using extracellular buffering agents to reverse or reduce exercise-induced acidosis and limit its impact on athletes' bioenergetic performance.
Regarding buffering agents used as supplements and ergogenic aids, these include sodium bicarbonate (SB), sodium citrate (SC), sodium lactate (SL), and calcium lactate (CL); the independent mechanisms of each of these substances will not be discussed here; however, all substances are ingested with the same objective: to increase the extracellular concentration of bicarbonate, which increases the extracellular efflux of H+, which contributes to acid-base balance during exercise, which can lead to performance improvement.
The ability to increase circulating bicarbonate to improve exercise capacity and performance has been widely studied. It is recognized that the most effective extracellular buffer is BS, with numerous narrative reviews and meta-analyses demonstrating its effectiveness, while there is limited data on the rest of the substances (CS, LS, LC).
The reality is that there is widespread controversy regarding the results of the trials along with a disparity in the magnitude of performance improvement using this type of substances. Therefore, it is important to determine the factors that can contribute to a person's response to these supplements.
Theoretically, any increase in bicarbonate would lead to a corresponding increase in buffering capacity; although we found that the minimum increase necessary to obtain performance gains is currently unknown. Carr et al. have suggested that an increase of +5 mmol/L from baseline levels is required to have a potential ergogenic benefit on exercise performance, while an increase of +6 mmol/L leads to certain ergogenic benefits alongside an increase in side effects. Despite this, no study to date has directly investigated the minimum increase necessary for performance improvements or the individual increases linked to changes in performance.
Saunders et al. determined whether there was any correlation between blood values (bicarbonate, pH) and exercise capacity. Surprisingly, we did not show any relationship between the magnitude of the change in circulating bicarbonate (or any other measure) and subsequent changes in exercise capacity.
Jones et al. observed that not all individuals reached a concentration of 5 mmol/L with a dose of 0.1 g · /kg, which could explain why this dose seems to be ineffective for performance improvement. However, a dose of 0,2 g · kg was effective in reaching this threshold in almost all individuals, although the concentration decreased at 60 minutes after ingestion (< 5 mmol/L) in some individuals. This could partially explain why a dose of 0.2 g · kg seems to be effective in some athletes, but not in all.
A dose of 0,3 g · kg of BS is the most commonly used in the literature and seems to come from the work of McNaughton et al., who demonstrated that it is the most effective compared to lower and higher doses. Although depending on the study, even reaching concentrations between 5 mmol- 6 mmol/L were not enough to improve performance (FIGURE 1).
FIG.1 Increases in blood bicarbonate from baseline after acute sodium bicarbonate supplementation, in order of magnitude of change. Data points indicate whether exercise performance was improved with supplementation (dark circles) or not (light circles).
This is due to additional factors that can explain this variation, including exercise patterns that determine H+ accumulation, genotype, associated side effects, and individual variation in response to supplementation.
Another factor of vital importance is the training level of the subjects, since if we are dealing with trained subjects we can correctly evaluate whether the benefits are from the supplementation itself because their performance levels are much more standardized and are more similar to each other, within the same athlete.
Few studies have investigated the effect of repeated supplementation in the same individuals using the same exercise protocol. Interestingly, only one person improved on all four occasions and nine others on at least one, suggesting that performance does not depend solely on the blood concentration of this substance.
A recent series of studies on acute BS supplementation suggest that it is unlikely that a uniform 'TIMING or time of intake' is optimal for all individuals.
Individuals should base their supplementary decision according to their own exercise demands and the likelihood of obtaining valuable improvement in it (these tasks will surely present more potential advantages or benefits by being continuous high-intensity exercise tasks, such as cycling of 4 km, swimming of 100 and 200 m, and rowing of 2.000 m, or intermittent high-intensity activities like those performed during team sports (for example, soccer, hockey, basketball, crossfit, etc…))
Another factor that may be relevant is the genotype:
The H+ that accumulate in the muscle during high-intensity exercise are predominantly removed by MCT1 and MCT4, through co-transport with lactate at a ratio of 1: 1. The sodium/hydrogen exchanger (NHE) system can also contribute to this process. It is widely recognized that increased bicarbonate in the blood enhances the activity of these transporters, increasing the efflux of H+ from the muscle and reducing muscle acidosis. Surprisingly, no study to date has directly measured the effect of increased circulating bicarbonate via supplementation on the activity of these transporters in humans.It is currently unclear whether the relationship between the increase in bicarbonate and the activity of these transporters is intrinsically associated.
We also know that lactate transport is elevated in athletes. This makes sense, as training interventions have been shown to increase the abundance and activity of MCT transporters. Additionally, lactate transport capacity (and subsequently H+ transport) was related to the amount of type I muscle fibers. MCT1 and MCT4 are expressed in human skeletal muscle, although MCT1 is more common in type I fibers and MCT4 in type II fibers. Polymorphisms in MCT transporters can also influence an individual's response to supplementation.
Regarding the associated side effects (one of the main problems of BS supplementation), the occurrence of gastrointestinal discomfort with these supplements is common: stomach aches, flatulence, nausea, vomiting, and diarrhea, etc.
This has obvious implications for athletes considering supplementation during competition and is a factor that probably contributes to the reason why the incidence of supplementation with such agents is low.
After the ingestion of BS, it dissociates in the stomach to form sodium (Na+) and bicarbonate, many of which are quickly neutralized with H+, producing carbon dioxide [CO2]. The production of CO2 in the stomach can cause gastric discomfort with the previously described symptoms. The authors report that this is typical at amounts above 0,3 g·kg, without concomitant increases in performance.
Therefore, it is evident that minimizing the discomfort associated with BS supplementation could increase the likelihood of a positive response, both at the individual and group levels. A potential solution is to ingest BS in enteric-coated capsules, avoiding neutralization in the stomach and the associated side effects. The timing of supplement intake may be a key modifiable component that can increase or decrease the likelihood of an ergogenic effect not only due to the increase in circulating bicarbonate but also due to the associated side effects.Since supplements are commonly ingested at a standardized time, often 60 minutes before the start of exercise as in the case of BS, this suggests that most studies may have forced athletes to exercise at a time when they experience enough discomfort to negatively affect their performance. Therefore, adopting an individualized bicarbonate supplementation protocol would likely avoid exercising when the associated side effects are most intense.
OPTIMIZING SUPPLEMENTATION
Overall, the data suggest that the timing of individualized supplementation with these agents may provide the best opportunity to achieve an ergogenic effect by matching the exercise timing with the peak bicarbonate concentration after the selected dose. Indeed, the supplement dose is another highly modifiable factor that could be adjusted to optimize supplementation.
Increasing SB doses above 0,3 g · kg results in an increase in the incidence of GI discomfort, while 0,1 g · kg seems insufficient to lead to improvements in exercise. Although 0,3 g · kg has long been considered the optimal dose. At a practical recommendation level, athletes who wish to supplement with these substances should try them outside of competition to see how it works for them, adapt, and optimize their individual supplementation strategies according to their needs and personal responses.
In conclusion
Knowing the ergogenic effects of these substances, several factors can modify their ergogenic effects, including the timing and dose of the supplements, the absolute changes in circulating bicarbonate, the exercise task being performed, MCT activity, training status, and associated side effects (FIGURE 2). Finally, more information is required about each supplement independently and its interaction with the individual, genotype, and environment.
Fig. 2 Summary of the factors that can modify the response to supplementation with sodium bicarbonate, sodium citrate, and calcium and sodium lactate.
Lthe dose (I) the timing of intake (II) influencing both the increases in circulating bicarbonate (III) and the associated gastrointestinal side effects (IV). The training status (V) genotype (VI) Along with the possibilities of a positive ergogenic response is also dependent on the duration and intensity of the exercise task performed (VII).
Bibliography
- Carr AJ, Hopkins WG, Gore CJ. Effects of acute alkalosis and acidosis on performance: a meta-analysis. Sports Med. (2011) 41:80114.
- Heibel, A. B., Perim, P. H., Oliveira, L. F., McNaughton, L. R., & Saunders, B. (2018). Time to optimize supplementation: modifying factors influencing the individual responses to extracellular buffering agents. Frontiers in Nutrition, 5.
- Lancha Junior AH, Painelli VS, Saunders B, Artioli GG. Nutritional strategies to modulate intracellular and extracellular buffering capacity during high-intensity exercise. Sports Med. (2015) 45(Suppl. 1):S71–81.
- McNaughton LR, Gough L, Deb S, Bentley D, Sparks SA. Recent developments in the use of sodium bicarbonate as an ergogenic aid. Curr Sports Med Rep. (2016) 15:233–44.
- Saunders B, Elliott-Sale K, Artioli GG, Swinton PA, Dolan E, Roschel H, et al. β-alanine supplementation to improve exercise capacity and performance: a systematic review and meta-analysis. Br J Sports Med. (2017) 51:658–69.
- Saunders B, Sale C, Harris RC, Sunderland C. Sodium bicarbonate and high-intensity cycling capacity: variability in responses. Int J Sports Physiol Perform. (2014) 9:627–32.
AUTHOR
Marcos Rueda Córdoba
- Graduate in Human Nutrition and Dietetics (UGR) and Official Master's in Nutrition in Physical Activity and Sport (UCAM). ISAK I Anthropometrist, Content creator and specialized courses in sports nutrition through online and in-person platforms. Teacher at Grupo San Valero (San Jorge University, Zaragoza)
- In-person Nutrition Consultation in Granada and online
