Marathon Fuel and Hydration: How Science Can Help Runners Avoid Hitting the Wall
Marathon runners frequently fall short of their goals due to inadequate fuel and hydration strategies. However, as explained by The Independent's sports editor Jack Rathborn, modern science is providing athletes with innovative tools to combat issues like cramps and the dreaded "wall." With the 2026 TCS London Marathon approaching, understanding these scientific advancements is crucial for runners aiming to optimise their performance.
The Personal Journey of a Marathon Runner
Jack Rathborn shares his own marathon experiences, having completed the London Marathon in 2021 and 2022 with times of 3:04. He finally broke the three-hour barrier at the 2024 London Marathon with a time of 2:56 and further improved at the 2025 Boston Marathon, finishing in 2:54. It was during these races that he fully grasped the importance of meticulous fuelling and hydration. In Boston, his sixth marathon, he successfully avoided cramping entirely, attributing this achievement to a scientifically informed approach.
The Role of Precision Fuel & Hydration
Precision Fuel & Hydration, a company with experience working alongside elite endurance athletes in running and triathlon, assisted Rathborn in developing a drastically different strategy. Their expertise highlights how science can build confidence in achieving sub-three-hour performances, even on challenging courses like Boston. One key service they offer is a sweat test, which measures an individual's sweat rate—a factor that can vary by up to ten times between people, from 200mg to 2,000mg of sodium per litre of sweat, largely determined by genetics.
Understanding the Sweat Test
The sweat test is a non-invasive procedure that takes approximately 45 minutes. It involves delivering a mild electric current to the arm via a strap, similar to a watch, which stimulates sweat production. Drops of sweat collect in a transparent disc, and the liquid eventually turns blue, providing a reading on a monitor. This test revealed that Rathborn is a "salty sweater," losing 1,146mg of sodium per litre of sweat during exercise. This information is critical for marathon runners, as it helps them avoid drastic dips in sodium or glycogen stores, which can lead to "bonking"—a state of exhaustion due to glycogen depletion.
Personalised Fuel and Hydration Strategies
Armed with scientific data, runners can tailor their marathon supplementation. For Rathborn, the recommendations included consuming up to 75g of carbohydrates per hour (a high intake), 1,000mg of sodium per litre of sweat (high intake), and 450ml of water per hour (moderate intake). Specifically, he was advised to take an electrolyte capsule every 30 minutes and consume 2-2.5 PF 30 gels per hour, totalling seven to eight gels over the marathon. This plan was substantially more than his intake during his first four marathons.
Application in a Real Race
At the Boston Marathon, Rathborn implemented this strategy by consuming one PF 30 Caffeine gel with 100mg of caffeine 15-20 minutes before the start, followed by six more gels every four miles (approximately 26 minutes). He included a second caffeine gel at 12 miles, resulting in 210g of carbohydrates over the three-hour race. Additionally, he took four salt capsules every 30-40 minutes and drank two gulps of water at nearly all of Boston's 24 water stations from two miles into the race. This method helped him avoid potential hurdles and enjoy the experience more fully.
Conclusion: Embracing Science for Marathon Success
By leveraging scientific insights from sweat tests and personalised hydration plans, marathon runners can significantly enhance their performance and avoid common pitfalls like hitting the wall. As Rathborn's experience demonstrates, a data-driven approach allows athletes to fine-tune their fuel and hydration strategies, turning marathon running from a puzzle into a manageable challenge. With practice, this method empowers runners to achieve their full potential and relish the race day experience.
