IRONMAN® World Championships

Fueling Highs: When racing in the heat of Kona, many athletes will experience GI discomfort if they consume the same amount of carbohydrate as they do in cooler conditions. This is because of the competing demand for blood flow in the body - namely the gut vs working muscles - and the skin and muscles’ need for blood trumps that of the gut. This shift in blood away from the GI system compromises the absorption rate of nutrition and results in issues like bloating and diarrhoea. Ben completed a heat acclimation protocol before heading to Kona to adapt his body to the notoriously hot and humid conditions. One of these adaptations will have been familiarising his body with this reduced blood flow to the gut, and adapting to reduce the shunt in blood away from the area, thus maintaining GI function. This hard work was evident in his fuel strategy execution, as he consumed ~160g/h (🤯) during the bike, and ~120g/h on the run. This supports the trend being observed in elite endurance sports that consuming >120g/h is now commonplace, and studies are investigating the physiology of tolerating versus absorbing these high carb intakes. Very high carb intakes are becoming more prevalent, with fellow PF&H athlete, Leon Chevalier, consuming ~150g/h during the marathon in Kona!

Fueling Lows: At the halfway point of the marathon, Ben felt his energy levels were “okay”, so when he picked up his PF 90 Gel from the personal needs aid station and noticed it was “boiling hot”, he decided to discard it. Moments later he felt a sudden crash in his perceived energy levels as he began running out of the ‘Energy Lab’ (ironic, we know). This low only lasted ~20 minutes, but was accompanied by some ‘rib flaring’, similar to a stitch, and was enough to significantly drop his pace, as he grabbed several on-course gels in an attempt to revive himself. Consuming ~180g of carb from gels in the final 10km shows how Ben pulled hard on the fueling lever of his nutrition plan, and it brought his energy levels up again. It’s worth noting that this extreme dose was likely unabsorbed by the end of the marathon, so keeping his intake higher in the earlier parts would be our recommendation going forward.

Ben’s high sweat rate in these conditions meant his net fluid and sodium losses would be significant, despite his relatively modest sweat sodium concentration. Consequently, after consulting with PF&H Sports Scientist Minty, Ben planned to slightly ‘over-salt’ his drinks, especially during the run when his sweat rate was predicted to exceed 2.5L/h. This higher sodium concentration will have helped two-fold; encouraging better retention of the high fluid volume he planned to consume, and compensating for his predicted high hourly sodium losses (potentially >2,400mg/h), especially as his fluid intake wouldn’t match his sweat losses. This worked well, and he felt his hydration strategy was the best part of his race, with a total intake of ~11.3L across the entire 8 hours.

There are some papers suggesting that endurance performance in the heat may be impacted by even moderate doses of caffeine. They suggest that core temperature may be further elevated with moderate caffeine doses (~5mg/kg), without enhancing performance. Very few of these research articles are conducted with elite athletes, who are known to be able to tolerate higher levels of core temperature increase, and Ben noticed no significant changes in his core temperature throughout the race. This further highlights the individual way that humans metabolise caffeine, and how it can affect us differently. To find out whether you should be using caffeine, you can check out this blog.