Bicarbonate: can it make your interval sessions better?

Bicarbonate for training?

With better dosing protocols and fewer side effects, researchers have been investigating bicarbonate supplementation once again, but this time in a wider range of situations. In the past, much of the research on bicarbonate supplementation looked at its use to improve time trial performance in a one-off event. However, what about its use in bouts of repeated high-intensity bursts of exercise such as interval training sessions? Could the ingestion of bicarbonate before an interval session help mitigate the rise in acidity during the session, thus allowing a greater number of high-quality efforts to be completed in a session – and therefore produce a greater training adaptation?

Actually relatively little research on this topic has been carried out. In a 1988 study on swimmers who ingested bicarbonate one hour prior to exercise, scientists reported a significant improvement in the 4th and 5th sprint of a 5 × 100-yard (91-metre) repetitions, with 2-minute passive rest periods in-between each effort⁽⁶⁾. Likewise, a 2006 study looked at recreationally trained women performing a program of cycling intervals over several weeks⁽⁷⁾. It found that bicarbonate ingestion produced greater improvements over time in both the amount of lactate the women could tolerate, and their performances in time to fatigue testing.

Another study investigated trained cyclists who performed four repeats of 2 × 4km cycling interval bouts in a simulated altitude (3,000m [~10,000ft]) environment⁽⁸⁾. Once again, the results suggested improved repeat exercise performance when bicarbonate was used. Further support for this notion came from a study on high-intensity interval training (HIIT) in college students where supplementation of bicarbonate (using 0.2 grams per kilo of body mass) before training sessions enhanced the effect of HIIT on anaerobic performance, and improved the blood lactate clearance rate⁽⁹⁾.

By contrast however, a number of studies have found no benefits of pre-exercise bicarbonate ingestion. These include:

·        A 2012 study where swimmers performing 6 x 100m intervals gained no significant benefit from bicarbonate ingestion⁽¹⁰⁾.

·        A 2020 study on repeated sprint performance in soccer players where bicarbonate ingestion produced no significant gains⁽¹¹⁾.

·        A 2013 study on rowers performing four weeks of interval training where pre-training bicarbonate ingestion did not improve overall performance gains⁽¹²⁾.

Unravelling the confusion

Why the disparity in findings? One reason is that the dosing and timing protocols in these studies differed from study to study. However, another reason may be to do with recovery in between interval efforts and the type of rest taken. Most of the above studies used passive rest intervals rather than active rest intervals (where rest periods consist of fairly gentle activity rather than complete rest – see this article).

But research shows that when it comes to repeated efforts, active recovery periods could lead to a faster and more complete acid-base balance recovery (ie clearance of acidity), and that this is particularly the case when bicarbonate has been ingested prior to exercise⁽¹³⁾. In plain English, the ability of bicarbonate to act as a buffer against acidity build up seems to be rejuvenated when active rest is taken in between efforts, which should mean superior performance in the later interval efforts when completing an interval session.

Testing the theory

To date, there’s been no in-depth research into the use of pre interval training ingestion of bicarbonate when the interval session uses periods of active rest. If this approach does enable athletes to perform a greater number of high-quality intervals, the training value of that session will be increased, which should over a period of time, lead to greater training adaptations and better performance. To test this theory, a brand new study by British scientists at the University of Birmingham has investigated the use of pre-interval training bicarbonate ingestion where the rest periods in between efforts are active rather than passive⁽¹⁴⁾.

Published in the European Journal of Applied Physiology, this study recruited 14 regionally competitive male swimmers who took part in a double-blind, randomised, crossover study (the most scientifically rigorous study design) performing interval sessions of 8 x 50m using active rest with pre-session bicarbonate or placebo ingestion. All the participants were trained swimmers who swam 7–10 times a week, accumulating 15–20 hours a week in total. Land-based training was also undertaken 3-5 times a week primarily consisting of resistance training. Participants competed in up to 12 competitions a year, which included national/international standard competitions, which required qualification through the British Swimming Association standards.

How the study was done

Following a familiarisation trial, the experimental trials were repeated on two occasions, seven days apart. Each participant was asked to swim 50m (front crawl), from a competitive diving block, at their maximum effort and repeat this every five minutes for a total of eight times. After each of the 50m sprints, participants swam a further 50m at their normal warm-up pace (ie easy) for the active recovery. They then rested until five minutes had elapsed whereupon they started the next 50m sprint. Importantly, this protocol replicated a typical training session for the squad, and was designed following consultation with both regional and national coaches in the United Kingdom. Sixty minutes before each trial, the participants ingested either:

·        Low calorie orange squash with added bicarbonate (0.3 grams per kilo)

·        A placebo (squash plus a solution of table salt at a strength that mimicked the taste of bicarbonate).

Importantly, no participants were able to identify which treatment they had received upon verbal questioning following each experimental trial – ie they were completely blinded. One week later the trial was repeated in the crossover phase, where those who had ingested placebo now ingested bicarbonate and vice versa.

In addition to measuring times for each of the eight intervals in both trials, the swimmers’ blood levels of lactate and bicarbonate were monitored, along with heart rates and perceived levels of exertion. Assessments for any symptoms of gastric distress were conducted every 10 minutes from ingestion to pre-exercise using visual analogue scales. These symptoms included nausea, flatulence, stomach cramp or ache, bowel urgency, diarrhoea, vomiting, stomach bloating, belching, headache, and thirst.

What they found

The key findings were as follows:

·        As expected, bicarbonate supplementation raised blood pH (ie less acid) and levels of blood bicarbonate both at 60 minutes after ingestion and post-exercise.

·        Regardless of whether bicarbonate or placebo ingestion, performance in each interval dropped off slightly (as expected) as the set progressed due to fatigue.

·        While there were no significant differences in performance during sprints 1-4, when bicarbonate was ingested, sprints 5-8 were completed progressively faster as the set went on compared to when placebo was ingested – ie the bicarbonate stemmed the fatigue-induced decline as the set progressed. The average improvement when bicarbonate was ingested was 0.5 seconds faster in sprint #5, 0.8 seconds faster in sprint #6, 1.0 second faster in sprint #7 and 1.4 seconds faster in sprint #8.

·        The beneficial effects from bicarbonate ingestion in sprints 5-8 were large enough so that the aggregated performance (sum times for the 8 sprints) was faster following NaHCO3 ingestion compared to placebo (see figure 2).

·        A few swimmers experienced gastric discomfort, which impaired their performance in the bicarbonate trial.

Figure 2: Aggregated times for the 8 interval efforts⁽¹⁴⁾

Practical implications for athletes

This study is interesting and relevant because it’s the first to show that the quality of an interval training session can be improved by prior ingestion of bicarbonate - IF the rest intervals include some active recovery. This has important implications; if the quality of an interval training session can be improved, the training adaptations (fitness gains) resulting from that training can be maximized⁽¹⁵⁾. In fact, there may even be a double-whammy effect since we know that the mere act of ingesting bicarbonate prior to exercise may help to upregulate the activity of genes involved in endurance adaptations⁽¹⁶⁾. It seems therefore that using bicarbonate to ‘turbocharge’ an interval training session could be a good option for athletes seeking maximum performance gains!

Having said that, there are some caveats worth mentioning. Firstly, while this was a high-quality study with a rigorous design, the number of participants was relatively small. Ideally, it would be good to see more studies on this topic with similar findings so we can be 100% confident about optimizing this protocol. Secondly, it’s worth noting that quite a few of the swimmers experienced a degree of gastric discomfort when taking bicarbonate. This is undoubtedly because the bicarbonate was ingested in one hit, rather than using a stepped approach.

If you want to try this protocol prior to interval training for yourself therefore, we highly recommend the stepped ingestion approach (figure 1) – NOT the one-hit approach! Note however that even with quite a few swimmers suffering gastric distress, the overall results in the bicarbonate trial were superior despite this distress. It’s reasonable to assume that had a stepped ingestion protocol been used, the performance advantage of using bicarbonate might have been even greater!

Another point worth mentioning is that while this protocol was trialled in swimmers, there’s absolutely no reason to believe it wouldn’t be equally applicable to any other type of interval session (running, cycling, rowing etc) where more than four intervals are performed in a set, and the intensity of the efforts is high. However, remember that the type of rest/recovery in between each effort in this study included a good slug of gentle but active recovery (to help dissipate accumulated lactate). So make sure any bicarbonate-fuelled interval sessions you perform is structured around active rather than passive rest!

References

1.       Int J Sports Med. 1984 Oct;5(5):228-31

2.       Sports Med. 1984 May-Jun;1(3):177-80

3.       Clin Sci (Lond). 1993 May;84(5):565-71

4.       Sports Med. 1994 Oct;18(4):268-80

5.       J Strength Cond Res: July 2012 - Volume 26 - Issue 7 - p 1953-1958

6.       Eur J Appl Physiol 58(1):171–174

7.       J Appl Physiol (1985). 2006 Sep;101(3):918-25

8.       Eur J Appl Physiol. 2018 Dec;118(12):2489-2498

9.       J Int Soc Sports Nutr. 2019 Apr 15;16(1):18

10.    J Exercise Physiol Online 2012. 15(6):84–92

11.    Int J Sport Nutr Exerc Metab. 2020 Sep 1;30(5):330-337

12.    Int J Sport Nutr Exerc Metab. 2013 Feb;23(1):40-7

13.    Int J Sports Med 2008. 29(07):545–551

14.    Eur J Appl Physiol (2023). doi.org/10.1007/s00421-023-05192-6

15.    J Physiol 2017. 595:2955–2968

16.    J Appl Physiol 2015. 119(11):1303–1312