London Marathon

Louise front-loaded her gels early, taking them at 5, 10 and 20km, alongside drinking PF Carb & Electrolyte Drink Mix in her marathon bottles picked up at the first five elite aid stations (also every 5km). She also picked up cola at the 30 and 35km aid stations, which meant that in total she averaged ~121g/h of carbohydrate across the full marathon. This is comfortably over the recommended 90g/h and a big step up from the ~78g/h she took on at the Amsterdam Marathon last October, a jump that required some serious gut training to tolerate. That intake is a big part of the story behind her performance, and she handled it well overall, but she flagged that the liquid carbohydrate seemed to cause her some discomfort this time around. Given that discomfort, it's worth trialling a slightly higher ratio of gels to drink mix in training, so she can hold the same high carb intake without leaning as heavily on the overconcentrated mix currently giving her more trouble.

Conditions on the day were mild compared to 2025’s unexpected hot temperatures, sitting around ~14°C (12-16°C) with ~74% humidity, so this wasn't primarily a heat-driven hydration challenge. On race morning, Louise opted to use sodium bicarbonate a couple of hours before the race, on top of 500ml of PH 1500 as a preload. This isn’t something we would recommend; she’s already getting a solid sodium dose (~3.3g of sodium) from the bicarbonate pre-race, and therefore the additional 500ml of PH 1500 beforehand is largely redundant and can come out of her routine. During the marathon itself, she took on ~788ml/h of fluid at a relative sodium concentration of ~1154mg/L (excluding the bicarb dose), notably higher than her 716mg/L sweat sodium concentration. That in-race concentration came from mixing her PF Carb & Electrolyte Drink Mix at three scoops per 500ml rather than the standard two. Notably, she was craving plain water by the finish, which also points to the in-race mix being more concentrated than she needed. Going forward, we'd suggest keeping her carbohydrate intake exactly where it is but aiming to reduce the concentration of her drinks so they are less electrolyte-heavy; for example mixing two scoops of PF Carb & Electrolyte Drink Mix with one scoop of PF Carb Only Drink Mix, so the sodium concentration in her drinks can come down independently of her carb intake. She did pick up a quad cramp from around 20km that forced her to ease off between 25-35km before rallying over the closing 7km, but doesn't believe this was sodium-related; cramp is rarely down to one single cause, with fatigue, pacing and conditioning all plausible contributors alongside her fuelling strategy.