By Jack Gray and Josh Elston-Carr

Editor’s note: We receive a lot of questions about using bicarb during hot races. We spoke with two high-level athletes to summarize the research and their personal experiences. Jack Gray and Josh Elston-Carr are both sub-elite runners from the UK and co-founders of FLYCARB, a startup dedicated to helping athletes perform their best through bicarb supplementation.

Both are long-time advocates of the “train hot, race cool” philosophy. Josh’s approach helped him secure 46th place in a time of 2hrs23mins at an unusually warm London Marathon this year.

What is Bicarb? Why does it matter for Endurance Sports?

Bicarb, usually taken as sodium bicarbonate, is a natural substance found in the blood that helps keep the body’s pH in balance. During intense exercise, your muscles produce lactic acid, which releases hydrogen ions that make the muscles more acidic. This acidity contributes to the familiar “burn” sensation, and loss of performance. Supplementing with bicarb increases the body’s buffering capacity, helping neutralize the acidic conditions. This helps athletes delay that burn, sustain power for longer, and recover faster between efforts.

Research on Bicarb Usage in Hot Conditions

Sodium bicarbonate has long been studied for its performance-enhancing effects in endurance sports, with its role as a lactate buffer well established (1). Recent research has also highlighted its potential to improve performance for athletes under heat stress. Studies have shown that sodium bicarbonate supplementation can support performance in hot conditions in the following ways:

• Reduces perceived exertion (2). This helps make races in hot conditions feel more manageable and allows athletes to sustain higher intensities with lower strain levels.
• Enhances recovery and performance in repeated efforts, helping sustain power output late in a race or across multiple events in a single day (3).
• Supports blood flow to the brain (4). This helps maintain focus and decision-making as fatigue increases in hot conditions.

In practical terms, the research suggests that bicarb supplementation can help athletes maintain control, reduce fatigue, and perform closer to their peak, even in hot, demanding conditions.

Real-world reports

At FLYCARB we’ve seen several excellent performances by athletes using our BICARRB product in hot conditions. For example, at the 2024 World Championships 100km in India, three members of the British men’s team relied on BICARRB to handle extreme heat and challenging terrain, helping them secure bronze medals.

We have also seen standout results over the marathon distance. At London 2025, Alex Milne ran 2:14:03, a 2.5minute PB, on an unexpectedly warm day. Later in the year he then went on to place 6th at the iconic, and hot, Comrades Ultramarathon. Fuelled by BICARRB, he moved through the field in the second half of both races, a testament to bicarb improving fatigue resistance in hot conditions.

Testing CORE and BICARRB Together

To see the effects firsthand, the FLYCARB team ran a small personal trial combining heat training with and without BICARRB. The test was conducted under controlled conditions for environment, clothing, and power output on an indoor cycling session. Using the CORE sensor we tracked skin and core temperature and Heat Strain Index. We also logged heart rate and perceived effort.

While the test was based on personal trials, our results echoed the scientific findings: during the test with BICARRB, perceived effort felt lower, core temperature and Heat Strain Index responses were more stable, and the session was more manageable overall. Notably, skin temperature was lower with BICARRB, suggesting a stronger sweat response.

The data for the trial is presented in the graph below, and both FLYCARB and CORE welcome dialogue with academic partners to further the research into the impacts of bicarb on exercising in hot conditions.

Conclusions

Research, athlete experiences, and personal trials show that bicarb can be a game-changer in hot conditions. Using bicarb supplements like FLYCARB’s BICARRB helps improve fatigue resistance, support more efficient breathing, maintain mental focus, and reduce perceived exertion. The BICARRB Energy Mix is also designed to protect the bicarbonate through stomach acid, eliminating gastrointestinal issues sometimes associated with bicarb.

About FLYCARB

Founded by UK runners Jack Gray and Josh Elston-Carr, FLYCARB is committed to helping athletes worldwide perform at their best through scientifically backed bicarb supplementation. The flagship product, BICARRB, is designed for precision, convenience, and performance, providing athletes with a reliable way to push their limits, even in extreme conditions. Learn more at [www.flycarb.com].

Citations

1. International Society of Sports Nutrition position stand: sodium bicarbonate and exercise performance
2. Sodium bicarbonate ingestion improves repeated high-intensity cycling performance in the heat - PMC
3. Sodium bicarbonate ingestion mitigates the heat-induced hyperventilation and reduction in cerebral blood velocity during exercise in the heat - PubMed
4. Sodium bicarbonate ingestion improves repeated high-intensity cycling performance in the heat - PMC