UTMB

The evening start at UTMB means that athletes eat and drink a lot more during the day of the race. Caleb stuck to simple carbohydrates throughout the day, avoiding unnecessary fat, fibre and protein, and sipping on plenty of PF Carb & Electrolyte Drink Mix right up until the evening race start.

For the race itself, Caleb had a deliberately simple fueling plan consisting of one PF 90 Gel per hour, topped up with the small amount of carb in his PH 1000 (Drink Mix) sachets, carrying enough across the race to hit 90-100g/h. Across 18:48:24, he took on just over 1.6 kg of carbohydrate, falling just shy of his pre-race target at ~87g/h.

PF&H Sports Scientist Minty was part of Caleb’s crew and weighed all of his nutrition before passing it to him, and again at each aid station after he’d returned his used flasks and empty wrappers. This allowed him to give precise feedback to Caleb during the race on how well he was sticking to the plan. On average, Caleb was getting ~85-90% of the contents of each gel, which is a solid effort given >10 hours of the race was in darkness! Those small leftover gel residues added up to more than two PF 90 Gels of unused fuel, or ~11g/h, and closing it would have put him at ~98g/h without adding any extra carbs to the plan.

The shape of his intake was intentionally front-loaded to match the unique intensity and topography of UTMB®. He fueled the opening 2:46 to Les Contamines at ~114g/h, matching the highest intensity of the race while his stomach was freshest, then settled down to a more sustainable intake, holding ~86g/h to Courmayeur, ~80g/h to Champex-Lac and ~80g/h onto Vallorcine. The ~69g/h over the closing two hours came while he was racing flat out for 2nd place. Being able to consume one single source of carbs at this rate for nearly 19 hours, with no flavour fatigue demonstrates Caleb’s exceptional gut-training, and suggests elite ultramarathon runners now significantly exceed the current ultra-running carbohydrate recommendations of 30-50g/h.

Caleb mentioned some fullness after leaving the Courmayeur aid station, which he reached at around 2am. Gastric emptying and splanchnic blood flow both fall during the night, so the small window of discomfort he reported was likely due to this. Reducing the volume he consumes at aid stations will also help keep GI comfort more stable and, hopefully, prevent the small amount of sickness Caleb experienced leaving Courmayeur.

Caleb didn’t preload with a strong electrolyte drink beforehand. With cold temperatures throughout the night, this likely didn’t negatively impact him much, but a PH 1500 in the ~90 minutes before the start remains an easy way to begin a race optimally hydrated, and on a warmer edition it would have mattered even more.

Conditions were cold by UTMB standards. The start and finish in Chamonix saw the highest temperatures of ~17°C, but the course spends most of the night above 2,000m and temperatures on Col de la Seigne, Grand Col Ferret and the Bovine ridge dropped to ~2°C, averaging ~8°C at ~75% humidity across the race. Caleb drank a little under 13L in total - drinking just over one Soft Flask per hour - that consisted of ~8L of PH 1000 (Drink Mix) and ~4.5L of plain water taken from fountains and aid stations between crew points to minimise the volume he had to carry at any point. His relative sodium concentration of ~653mg/L was almost identical to his measured sweat sodium concentration (655mg/L), which is an impressive balance to maintain over almost 19 hours of racing.

What stands out is how closely his intake tracked thermoregulatory demand rather than a fixed hourly schedule. He drank ~1L/h over the opening 2:46 to Les Contamines while it was still warm in the valley and he was working hardest. This dropped to ~490ml/h through the coldest overnight section to Courmayeur, then returned to ~670ml/h once the sun came up over Grand Col Ferret and as he descended into the Swiss valleys, holding a similar volume toward Vallorcine. That is what drinking to thirst looks like when thirst has been properly calibrated against known sweat rates measured along the course, in similar temperatures. Passing urine occasionally throughout the race, and relatively shortly after finishing, is a reasonable sign he arrived in Chamonix without a large fluid deficit.