Izzi's headline numbers
Carbohydrate is the main fuel you burn when racing. Failing to fuel properly is a leading cause of underperformance in longer races.
Izzi started training her gut by increasing the number of gels she’d take on her longer runs during key sessions in the weeks leading up to Valencia. She also practised specifically with the PF Carb Only Drink Mix, hitting ~60g of carb an hour, as this was her plan going into the marathon. Because of her ‘sub-elite’ classification, she was able to prepare eight bottles for the aid stations on course and fill them with a higher concentration of carb drink mix to hit an average of 66g/h, drinking most of each bottle. She carried three PF 30 Gels as back-up fuel in her top, but didn’t end up taking them as she was able to successfully grab each of her bottles. We’d recommend continuing her gut training as the science would suggest an increase in carb intake may benefit her performance.
Taking on board an appropriate amount of fluid and sodium is essential to maintaining blood volume and supporting the cardiovascular effort needed to perform on race day.
Whilst the absolute amount of sodium and fluid consumed per hour is important, it’s critical to consider these in relation to each other. This is known as 'relative sodium concentration' and it’s expressed in milligrams per litre (mg/L). How much sodium you’re taking in per litre of fluid is more important than the absolute amount taken in per hour.
In previous races, Izzi has struggled with cramping and it’s possible that this has been caused by her not replacing enough of the sodium that she loses in her sweat, so she was keen to ensure she started well hydrated by preloading her sodium intake the night before and morning of this one. She distributed one litre of fluid across her eight bottles and consumed almost all of it alongside a small amount of sodium. Across the marathon distance and in these mild conditions, the low sodium concentration didn't seem to negatively impact her performance. Izzi has started looking more at her sweat rate and can lose over two litres per hour in different conditions. For warmer races, she would likely need a more proactive fluid and sodium replacement strategy, and additional sweat rate and sweat sodium data would be helpful, too.
Beyond the Three Levers of Performance (carb, sodium and fluid), caffeine is one of only a few substances that is proven to improve performance for most endurance athletes as it can help stave off mental and physical fatigue.
Izzi had two coffees during the morning of the race, but opted not to use additional caffeine closer to the start this time as she was concerned it may upset her stomach like it has on occasion. However, her race strategy has evolved overall since then, so she's open to trying caffeine again in training ahead of future races. The science suggests that she may benefit from a dose before taking off and from swapping one or two of her carried gels for caffeinated ones.
How Izzi hit her numbers
Here's everything that Izzi ate and drank on the day...
Izzi's weapons of choice
Izzi's full stats
There is good confidence in the accuracy of the data reported. An athlete feels that the numbers closely reflect what they consumed despite a couple of estimations which may carry some degree of error. The majority of what was consumed is recorded to a high level of specificity (most volumes are known through the use of bottles brands quantities flavours). The numbers are very plausible and align with previous data recordings (if an athlete has collected data previously).