The London Orbit

This was slightly different from Jenson's ‘usual’ races, as it was an attempt to break a 'Fastest Known Time' circumnavigating London by gravel, racing against two presenters from Global Cycling Network (who had a two-hour head start!). But, he started his morning in a familiar manner with a carb-rich breakfast to set him up for a long day in the saddle, with a porridge pot and a bowl of cereal, topped up with a PF 30 Chew in the final half hour. Across almost 14 hours of cycling he then averaged ~116g/h of carbohydrate, mainly from PF 30 Gels, PF 30 Caffeine Gels, PF 30 Chews and PF 60 Chew Bars, with some sweets and energy drinks incorporated to add some variety and flavour changes through the day. This is a rate far above what was once thought to be a ~90g/h ceiling and building up to this kind of intake takes gut training to tolerate well, which Jenson did as he didn’t have any GI issues at all across the day.

Since we know Jenson’s average power across the effort, the race duration and his body mass, we are able to estimate values for his carbohydrate oxidation rate; putting his physiological ceiling at ~109-129g/h depending on exactly how that power is expressed and the make-up of his carb sources. His actual intake landed almost exactly in the middle of that band, so this wasn't just a high carb rate he happened to tolerate, it was fueling at a level he was able to utilise to support his performance and energy levels.

Reassuringly, this is also supported by the raw energy numbers: at ~1,669g total, his carbohydrate intake alone supplied roughly 6,676 kcal (at 4 kcal/g), around 68% of the 9,859 kcal his cycling computer logged for the whole effort. This is slightly above the ~58-60% of energy burn we estimate came from carbohydrate oxidation - a good sign that he wasn't running down his glycogen stores.

With temperatures peaking at 31°C (88ºF), Jenson's fluid intake totalled an impressive ~15.8 litres across the day. Taking his power output, body mass and the day's actual hour-by-hour weather, we can estimate his total sweat loss at ~16.2L over the day (an average rate of ~1.16L/h). Based on those estimates, his intake replaced the large majority of what he lost, leaving him only ~0.5% down on body mass by the finish, comfortably inside safe limits of dehydration. For roughly 10 of the ride’s 14 hours, from mid-morning to early evening, the surrounding air likely heated Jenson’s skin faster than airflow could cool it. In other words, the usual cooling effect of moving air was reversed, so sweat evaporation had to dissipate both the heat produced by his body and the additional heat gained from the environment.

Jenson’s sodium intake came predominantly from PH 1500 in his bottles and hydration packs, and he coupled this with water and other low-sodium caffeinated energy drinks so that his relative sodium concentration worked out at ~759mg/L. This is slightly below his known sweat sodium concentration, but not so much to negatively impact his performance.

Overall, though, this was a well-executed hot-weather hydration plan that kept him clear-headed all the way to the finish.

Jenson's caffeine intake totalled 416mg (~6.03mg/kg), coming from two PF 30 Caffeine Gels, some energy drink and cola, spread across the back half of a near-14-hour effort. That sits right at the top of the commonly cited 3-6mg of caffeine per kilo of bodyweight guidance for endurance performance, and spreading the dose across several hours rather than front-loading it is a sensible way to maintain caffeine levels in the blood. With no reported tolerance issues, his system handled it well, but there's little headroom to push the dose any higher without moving outside the evidence base.