The Effects of Sodium Bicarbonate on Endurance Performance
By Meg Smith, Physiologist & Doug Stewart, Performance Director
In 2018, the International Olympic Committee consensus statement classified sodium bicarbonate as ‘a supplement with good evidence of benefits for exercise performance’ (Maughan et al., 2018). Sodium bicarbonate has been used by endurance athletes to improve their performance, but there is little scientific literature to test its effectiveness. Working with Meg Smith, Physiologist at Loughborough University Sport Services, we developed a testing protocol to look into the effects of sodium bicarbonate on endurance performance.
Sodium Bicarbonate: Context
The general ergogenic effects of SB supplementation are well established, with the most pronounced performance enhancement being observed in high-intensity sporting tasks lasting between 1 – 10 min (Maughan et al., 2018). Strong evidence supports the use of SB as an ergogenic aid during multiple high-intensity bouts of exercise that have a high anaerobic metabolic demand. However, its application into endurance performance (or any performance lasting over 2 hours) remains unexplored (Carr et al., 2011).
How Does Sodium Bicarbonate Work?
SB is a buffering agent that is suggested to improve performance by promoting the efflux of lactate and H+ ions from working tissues (working muscles) into the blood. Following ingestion of SB, the concentration of blood bicarbonate increases, acting as the buffer that helps maintain extracellular and intracellular pH (Lancha et al., 2015). During exercise, the greater levels of circulating bicarbonate are accompanied by:
Increased blood pH
Increased transportation of hydrogen ions (H+) and lactate out of the working muscle and into circulation (see figure 1).
Figure 1. Upregulation of rate of removal of H+ ions out of the muscle. Image source: mysportscience.com
So, how exactly does this work?
When we exercise, hydrogen ions begin to accumulate in the muscles, causing them to become more acidic.
This increased muscle acidity and build-up of metabolites causes fatigue, which leads to reduced performance.
SB acts as a buffer in the blood, causing the efflux of H+ ions out of the muscle and into the blood, which is therefore reflected in a higher blood lactate concentration.
The upregulation in the rate of removal of H+ ions from the active muscles delays exercise-induced acidosis, which has been linked with a delay in the onset of fatigue.
The Case Study: UTMB Simulation
Route profile © utmb.world
To test the impact that supplementing with sodium bicarbonate can have on endurance performance, we designed a protocol that would simulate the first 23 km of the Ultra-Trail du Mont Blanc (UTMB) - so to just after St Gervais.
Covering around 170 km and c. 10,000 m of elevation gain, the UTMB is the 100-mile final of the UTMB World Series and arguably the major ultra running event on every professional or amateur runner’s calendar. It circumnvavigates the Mont Blanc massif, passing through France, Italy, and Switzerland. The first 23 km present c. 900 m of ascent. This is what we covered in the lab test, where Performance Director Doug was the test subject.
Doug repeated running a simulation of the first 23km of the UTMB route in a range of different environmental conditions and following different supplementation protocols, so that we could attempt to understand the effects of SB in conditions that matched those of the UTMB:
· Normoxia (sea level), no supplementation
· Hypoxia (altitude, 1000m), no supplementation (control)
· Hypoxia + SB
· Normoxia + SB
Doug ate the same number of gels/grams of carbohydrate at the same time point, and matched fluid consumption for all trials. So, each trial was identical from a fuelling perspective. In each trial, Doug ran identical speeds for each section of the course. So, total time of each trial was identical.
24 hours prior to all lab visits, Doug standardised the following as best he could:
- Same diet
- No caffeine before 9am on day of lab visit
- 25-minute easy run the day before the lab visit
Doug used the Maurten Bicarb system as his SB supplementation during these trials.
During the trials, we took the following measurements:
· Blood lactate
· Heart rate
· RPE (rate of perceived exertion)
· Oxygen Saturation
· Substrate utilisation
Key findings
We will focus on the trials where we simulated the altitude and typical temperature of UTMB, but is worth noting that a similar set of results were discovered in the Normoxia (sea level) tests.
Blood Lactate
At altitude, blood lactate concentration was higher in the trial where Doug had consumed SB (solid line).
This is due to a more efficient buffering process occurring during exercise. Therefore, this suggests the SB had an impact on Doug and could be a worthwhile performance aid.
However, it needs to be trialled further and intake balanced with potential GI discomfort.
Heart Rate
Heart rate was ~4% higher in conditions where Doug had consumed SB (solid line in the graph). What’s interesting to note, however, is that this difference in HR is more significant when working at submaximal intensities / heart rates. It appears that this difference is to a certain limit of intensity, where % of max HR ultimately becomes the limiter and, as the red circles indicate, the difference between the supplemented trial and non-supplemented trial seems to disappear (due to exercise capacity being limited by max HR).
In conclusion, heart rate will increase at submax intensities when taking SB and based on this data, there could be a 4-5% difference.
Carbohydrate oxidation
We found that carbohydrate oxidation was higher in conditions where Doug consumed SB (solid line).
This indicates that, at higher heart rates, in conditions where SB was consumed, there is less fat oxidation and therefore a heavier reliance on carbohydrates as a fuel source. This is important to consider, as it could have an impact on the fuelling strategy you design and affect the types of races you choose to supplement with SB for (i.e. SB would have less of an impact on substrate utilisation in flatter races at sea level).
RPE (Rate of Perceived Exertion)
When Doug supplemented with SB, RPE was lower on the steeper incline compared to when there was no SB supplementation.
During the hypoxic trial with no SB supplementation, Doug complained of ‘burning’ sensations, in his calves specifically. However, when Doug completed the hypoxic trial and took SB, the burning sensation was not as bad.
Despite ventilation rate and RER being higher in the supplemented trial (more than likely because Doug ran part of this), RPE was still lower. The respiratory exchange ratio (RER) is the ratio between the metabolic production of carbon dioxide (CO2) and the uptake of oxygen (O2). The ratio is determined by comparing exhaled gases to room air.
This could have been due to a training / placebo effect, however, with the higher RER and ventilation rate indicating that, physiologically, the exercise was more demanding.
—
While this case study did provide some really interesting findings to consider in relation to performance, there are a couple of limitations that need to be considered:
· Sample size: n = 1
· No time trial conducted before and after the trial, to determine whether there was a performance benefit
· Not possible to blind Doug to the Maurten Bicarb product
· Potential learning effect across the trials (possibly affecting RPE)
· Not completely controlled: we did what we could within our means!
Summary and Future Implications
Heart Rate
HR will increase at submaximal intensities when SB supplementation has been used. Based on Doug’s data, this could reflect a ~4-5% increase in HR. This will be important to consider if your pacing strategy is based on HR.
Blood Lactate
Blood lactate concentration increases when SB supplementation has been used. This is due to more efficient buffering. This could be a worthwhile aid for performance; however, it is really important to trial this and ensure you balance SB intake with GI discomfort.
Carbohydrate Oxidation
Carbohydrate oxidation is higher when SB supplementation has been used. This means that your fuelling rate may have to increase to meet this extra demand. This could affect the nature of races you decide to supplement with SB.
RPE
The supplemented trial felt easier during the steepest climb, and Doug felt as though his legs didn’t experience as much of a burning sensation as when he had not used SB. This could, however, be due to some learning effect and the fact that Doug was not blinded to the SB product.
References
Maughan RJ, Burke LM, Dvorak J, et al. IOC consensus statement: dietary supplements and the high-performance athlete. Br J Sports Med. 2018;52(7): 439–55.
Carr AJ, Hopkins WG, Gore CJ. Effects of acute alkalosis and acidosis on performance: a meta-analysis. Sports Med. 2011;41(10): 801–14.
Lancha Junior AH, Painelli Vde S, Saunders B, et al. Nutritional strategies to modulate intracellular and extracellular buffering capacity during high-intensity exercise. Sports Med. 2015;45(Suppl 1): S71–81.