The progression, week by week
Each row is a week. The grams per hour figure is what you rehearse in the long sessions, not in every workout: short and hard sessions do not need it. The minimum duration shown is the time the session needs for the rehearsal to mean anything.
| Week | Target | Minimum session | What you do |
|---|
The last two weeks deliberately add nothing: they are for repeating the race plan exactly as written, with the same product, the same spacing and the same intensity. If a week sits badly, do not move on: repeat the same figure and carry on from there.
What gut training is and why it works
When someone says that gels do not agree with them, they are almost always saying two things at once: that they took more than they absorb, and that they had never taken that much before. The second one is fixable, and the fix is called gut training: exposing the digestive system, repeatedly and progressively, to the amount of carbohydrate you will need on race day.
It is not a trick or a fashion. It is the same logic you apply to any other system: if you have never run more than 15 km, the marathon is going to hurt; if you have never taken more than 50 g of carbohydrate per hour, the 90 g/h in a 70.3 plan will hurt just the same, only somewhere else.
What actually changes in there
Three things, all of them measurable.
More transporters. Glucose crosses the gut wall through SGLT1 and fructose through GLUT5. Repeated exposure to those sugars increases the number of transporters available, especially GLUT5, which is the more trainable of the two. That is where the room to go from 60 to 90 g/h, and from 90 to 120, comes from.
Faster gastric emptying. The stomach gets used to the volume and the concentration, and learns to pass the contents on without leaving that brick feeling behind.
Fewer symptoms for the same load. Part of the improvement is not absorption, it is tolerance: the same amount produces less bloating and less urgency because the system already knows it.
How much you can add per week
The rate this calculator uses is 5 g/h per week with one long rehearsal session, 8 with two and 10 with three. It is deliberately conservative. You can go faster, and the literature has protocols producing noticeable change in two weeks, but the cost of overshooting is high: a session with digestive problems is not only lost, it leaves behind the mistrust that stops people trying again.
The last two weeks of the plan add nothing. They exist so you can rehearse the full race plan twice, with the exact product, at the same time of day and at competition intensity. That rehearsal is worth more than the two weeks of climbing it replaces.
On the total jump: going from 50 to 90 g/h is a normal goal for one training block. Going from 40 to 120 is not. If the jump you are asking of the plan is more than about 50 g/h, consider doing it across two seasons or settling on a figure you can sustain without thinking about it.
How you rehearse it, in practice
Only in the long sessions. The stimulus comes from a carbohydrate load sustained over hours, not from one gel inside a 40 minute interval set. Two long sessions a week is a good maximum; three only makes sense in heavy blocks.
With the race product. Different brands use different blends, and the adaptation is partly sugar specific. Training on cheap maltodextrin to race on a high fructose product wastes half the adaptation.
At race intensity. Blood flow to the gut drops as intensity rises: what you tolerate riding easy is not what you tolerate at race pace. On the bike that is easy; running, where most symptoms appear, deserves at least one long session at target pace.
Writing down what happens. What you took, when, how much, and how it sat, on a scale of nought to ten. Without that log, in week six you will not remember whether the problem was the caffeine gel or breakfast.
Once you have the figure, the actual split of bottles and gels comes out of the session plan calculator.
The limits, and what to do when you stall
The ceiling depends on the product: 60 g/h with glucose or maltodextrin only, around 90 with a 2:1 blend and up to 120 with high fructose 1:0.8 blends. No progression helps if the product cannot go further, and that is the first thing to check when the plan stalls.
Then come the causes that are not gut related: fibre the day before, anti-inflammatories before training, dehydration, heat. The first three multiply symptoms and have nothing to do with the amount of carbohydrate. If everything sits badly on one particular day, look there before lowering the figure.
And one piece of common sense: if significant or persistent digestive symptoms show up outside training, this is no longer a question of grams per hour and the answer is not in a calculator.
Frequently asked questions
What is gut training?
It is exposing the digestive system, repeatedly and progressively, to the carbohydrate per hour you intend to take in competition, so that on race day it absorbs it without symptoms. It is done in the long sessions, climbing gradually over several weeks and using the same product you will carry.
How long does it take to notice?
The first changes in tolerance appear within two or three weeks of regular exposure. Reaching a high figure and holding it comfortably takes longer: going from 50 to 90 g/h with two long sessions a week is about five weeks of progression plus two of consolidation. The adaptation also fades if you stop stimulating it for months.
Can you really reach 120 g per hour?
You can, but only with a high fructose blend around 1:0.8, in long events and after a progression of several weeks. With a 2:1 blend the practical ceiling is 90 g/h, and with glucose only products it is 60. It is also worth asking whether you need it: above 90 g/h the extra benefit is small except in events lasting many hours.
Do I have to train like this every day?
No, and it would backfire. The stimulus comes in the long sessions, one or two a week. In the rest of your training, and even in some easy long sessions, some athletes prefer the opposite: training with low carbohydrate availability to trigger other adaptations. Both live happily in a well built plan, in different sessions.
What if one week sits badly?
Repeat that same figure the following week instead of climbing. If it happens again, drop one step and check the usual suspects: fibre the day before, coffee, anti-inflammatories, hydration and heat. Also the spacing: 90 g/h in feeds every twenty minutes sits better than the same 90 g in two gels back to back.
Does it work for running or only for cycling?
Both, but running is harder on the gut: impact and posture mean more symptoms for the same amount. That is why plenty of athletes tolerate 90 g/h on the bike and no more than 60 running. If your race finishes on foot, at least one rehearsal session a week has to be a run.
When do I start it within the season plan?
With enough room for the last two weeks to be race plan rehearsals rather than increments. Adding the progression and the consolidation, count on six to ten weeks before the target race. Doing it in race week is not gut training, it is a gamble.
Disclaimer and privacy
This calculator is an informational estimate and does not replace a coach or a laboratory test. Nothing you type ever leaves your browser.
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