London Marathon

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.

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!

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.