Coastal Challenge

Pierre comfortably handled a high carbohydrate intake across all five stages of the Coastal Challenge, even amidst the hot and humid conditions in Costa Rica. His consistent gut training in similarly hot environments helped maintain gut blood flow, which typically decreases as the body redirects blood to the skin for cooling. Dehydration progressively lowers blood flow to the gut, so his ability to absorb carbs on the day is even *more* impressive. His average hourly carb intake ranged from ~74g/h during the final stage to almost double that (~133g/h) during stage three. Pierre effectively pulled all three nutritional levers by using a ‘decoupled’ strategy at times, and then also incorporating mildly isotonic drinks at points to ensure a steady carb supply as well as a high fluid intake.

Pierre has measured his sweat rate in similar conditions and lost >2L (64oz) per hour, which is relatively high but not unexpected given his ability to run fast (high level of fitness). Combined with his high sweat sodium concentration, he knew that prioritising hydration would be critical in Costa Rica’s heat and humidity. Sweat is hypotonic, meaning it’s lower in sodium concentration than the blood. As we lose more fluid than sodium through sweating, plasma sodium concentration *increases*. This can cause water to be pulled from the space in between your cells and back into the bloodstream to balance the osmolality, which can impair muscle function and exacerbate dehydration. Pierre experienced some severe dehydration symptoms at the finish line of stage four, potentially due to a combination of factors: a) his extremely high sodium intake (>3,100mg/L on stage four), b) drinking over ~1.3L per hour, c) accruing an extreme level of total body mass loss, where he finished at ~6% lower than his starting body weight. While it’s difficult to pinpoint the exact cause, reducing sodium intake to better align with his known sweat sodium losses would likely help mitigate dehydration symptoms in future races.