Don’t Banquet on the Bike
Many Ironman marathons are ruined by nutritional issues, and nine times out of 10 the specific nutritional issue is consuming too much rather than too little. Triathletes very often overestimate both the amount of nutrition they need to get through an Ironman and the amount their bodies can actually absorb and use.
If you can take in 60g of carbohydrate and 750ml of fluid per hour on the bike, which is very easy to do with nothing more than a sports drink, you should be fine. Few athletes can absorb and use more than 80g of carbs per hour. If you’re a bigger athlete and your race takes place on a hot day, you may need 1 to 1.2 liters of fluid per hour to prevent a dehydration-related slowdown. But 80g of carbs per hour and 1 to 1.2 liters of fluid per hour are still a lot less than many triathletes try to cram down.
The rub is that the body can absorb a lot more fluid and carbohydrate during cycling than during running due to the stomach jostling involved in the latter. So what happens is that competitors take in as much nutrition as their bodies can handle on the bike, then hop off and start running only to be hit with nausea, bloating and worse. So be careful not to overdo your nutrition intake in the last hour of the bike leg so your gastrointestinal system won’t declare mutiny at the start of that all-important marathon.
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