Fuelling, Sprint to Full Distance.

An athlete told me his stomach had ruined his 70.3. He had taken four gels on the bike, which was what the plan said, and by the run he could not keep anything down.

I asked how many gels he took on a normal long ride in training. None. He did not like taking them in training because it felt unnecessary.

His stomach had not failed. It had been asked to do something it had never once practised.

Your gut is a trainable organ. Almost nobody trains it, and then they blame it on race day.

Distance Changes the Question Completely

A sprint triathlon needs essentially nothing. You have enough stored glycogen for an hour of hard work. Take some fluid, take a gel if it makes you feel better, and stop thinking about it. Athletes who plan elaborate fuelling for a sprint are solving a problem they do not have and often creating one.

Olympic distance, you want something. Sixty to ninety minutes of riding at a decent intensity is worth thirty to sixty grams of carbohydrate an hour, mostly on the bike.

Middle distance is where it starts to be decisive. You are out for four to six hours and you cannot store enough to cover it. Sixty to ninety grams an hour, and this is where gut training genuinely matters.

Full distance is a different sport. Nine to fourteen hours, and fuelling is not a supporting detail, it is one of the main events. Realistically eighty to a hundred and twenty grams an hour for a well-prepared athlete, and getting that in requires a stomach that has been built up to it over months.

Why the Gut Is the Limit

There is a ceiling on how fast you can absorb carbohydrate, and it is not fixed. It depends on the transporters in your intestinal wall, and those upregulate with repeated exposure. Feed a gut regularly at high rates and it gets better at it. Feed it nothing for three months and then ask for ninety grams an hour while your blood is diverted to your legs and you are bouncing along a road, and it will decline.

There is also a trick worth knowing. Glucose and fructose use different transport routes, so a mixed source lets you absorb more in total than glucose alone. That is why modern products advertise a ratio, and it is genuinely the mechanism behind higher intake rates rather than marketing.

So gut training is simply doing your long sessions at race intake, every time, for months. Not occasionally. Every long ride and every long run, at the rate and with the products you intend to use.

Where It Goes in the Race

The bike is where you eat. It is the only leg where your stomach is relatively stable, you are in a fixed position, and you have hours. Front-load it. Most of your total intake for the day should go in during the ride, and the biggest mistake I see is athletes waiting until they feel like they need it.

By the time you feel like you need it, you are behind and you will not catch up. Start eating within the first twenty minutes of the bike, on a schedule, whether you want to or not.

The run is damage limitation. Your stomach is being shaken, blood flow to the gut is lower, and tolerance drops sharply. Liquids and gels only, small and frequent, and expect to take in less than you planned.

The swim is nothing. Do not attempt anything clever.

Fluid and Sodium

Work out your sweat rate rather than guessing. Weigh yourself naked before a one hour ride, weigh again after, account for anything you drank. Every kilogram lost is roughly a litre of sweat.

Do that once in cool conditions and once in warm, and you will know more about your hydration needs than any general guideline can tell you.

Then drink to roughly match, and take sodium with it, particularly in heat and particularly if you are a salty sweater. Overdrinking plain water over many hours is genuinely dangerous and is a real risk at full distance.

The Rules I Give Everybody

Nothing new on race day. Not a flavour, not a brand, not a bar. Whatever is on the course, assume you cannot use it unless you have trained with it.

Rehearse the exact plan on your longest sessions, including the timing, so that on race day you are executing something familiar rather than improvising.

Write it down and put it on your top tube. Under fatigue, at hour four, people forget. A schedule taped where you can see it removes a decision.

And build up gradually. If you currently take thirty grams an hour, do not attempt ninety next Saturday. Add ten or fifteen grams an hour every couple of weeks and let the gut catch up.

The Bottom Line

Sprint, do not overthink it. Middle and full distance, the plan is only as good as the number of times you have rehearsed it.

Eat on the bike, early and on a schedule. Keep the run simple. Know your sweat rate rather than guessing. And train the gut like you train everything else, because on the day it is as likely to be your limiter as your legs are.