David's headline numbers
David's strategy
Fueling
T - 1-4hrs: Ate a carb rich meal (Low in fat & fibre)
David would benefit from taking in a final dose of carb <30 minutes before
"I ran on the limit the whole way."
Dave has used a Supersapiens [continuous glucose monitor]() to measure his response to carbs before races, and he found he was experiencing [rebound hypoglycemia]() when taking any carbs within 2-3 hours of exercise. So, he decided to rely on his carb-heavy breakfast alone, instead of adding a pre-race gel. During the race, Dave averaged ~78g of carb per hour through a range of [PF Gels](). This is nearly bang on the ~75g/h recommended by our [Fuel & Hydration Planner](), and worked well for him, considering his energy levels were high all day, and his glucose trace showed a stable level throughout.
Hydration
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.
David1003mg/L
David has been Sweat Tested to dial in his hydration plan
Sweat sodium concentration (mg/L) is largely genetically determined and remains relatively stable. Knowing how salty your sweat is enables you to replace a good proportion of your sweat losses, which can range from 200-2,000mg/L.
Whilst David's losses are on the moderate side, getting his hydration strategy right is still important if he wants to perform at his best.
Learn moreDrinking a strong electrolyte drink before the race could have helped David start optimally hydrated
"I don't usually drink much during races, but I never felt thirsty"
Dave didn’t complete our usual preloading protocol, but did take some sodium bicarb with his breakfast which contained a very large dose of sodium (~5,200mg) and ~40g of carbohydrates. Thankfully this extreme amount didn’t cause him any gastrointestinal (GI) issues like high doses of sodium and sodium bicarb often do. We’d recommend a relative sodium concentration of ~1,500mg per litre the night before and morning of the race as research has shown this to be an optimal concentration for inducing hypervolemia, minimising the risk of GI distress. Interestingly, Dave also felt like he needed to pee a couple of times before the race, which can sometimes be prevented by adding some sodium to the pre-race drink. To reduce the risk of dehydration toward the end of a race, Dave has been working on increasing his fluid intake. In London, he drank the most he ever has during a marathon, but still only averaged ~56ml of water per hour. Even though temperatures were mild, this is still a *very* small intake compared to the average consumption from all of our marathon case studies (~356ml per hour). Dave did start to experience minor cramping in his hamstrings at ~37km (24 miles). We know he loses 1,003mg of sodium in each litre of his sweat, and he didn’t take any electrolytes during the race, so perhaps including some sodium during the race may have helped prevent the muscle cramps although it is likely the cramps were largely caused by muscle fatigue!
Caffeine
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.
T - 0-4hrs: Had a final hit of caffeine
Dave’s caffeine intake was appropriate, with a large black coffee pre-race to get his blood caffeine levels up, followed by a 200mg mid-race boost from Caffeine Gels. He averaged ~2.38mg per kg of bodyweight, which is slightly below the 3-6mg/kg recommended by the literature. However, as the race was only 2 hours 42 minutes long, it’s likely this was enough to reap the performance benefits associated with caffeine.
How David hit his numbers
Here's everything that David ate and drank on the day...
Final thoughts
“Tough, but I loved it!”
“As the Director of Applied Science and Content at Supersapiens and part of the SuperPrecise team boxing off Spring marathons in 2023, Dave managed to set a shiny new personal best marathon time at London running 2:42:53. He did this while crushing his fueling plan to a tee, and drinking more than he’s ever done before during a race of this distance. There are a few small areas to optimise in Dave’s fuel and hydration strategy, including his overall fluid consumption and adding electrolytes to help fight dehydration and aid with carb absorption. ”
PF&HDavid's full stats
Data Confidence
We rate each of our case studies from 1-5 based on the level of accuracy, and our confidence in the data.
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).