Fuelling During Long Sessions: Carbs Per Hour and Training Your Gut

The back half of a long session is decided by glycogen maths

A trained adult stores roughly 400-600 g of carbohydrate as muscle and liver glycogen, enough for somewhere between 90 and 120 minutes of continuous moderate-to-hard effort before stores run low. Nothing about willpower changes that number. Once glycogen drops, pace fades, focus goes, and the last third of a long run or ride gets harder for reasons that have nothing to do with how well the first two-thirds went.

This is why in-session fuelling matters so much more than most athletes treat it. A perfectly paced first two hours can still unravel in the third if carbohydrate intake has not kept pace with the clock. The fix is not complicated: know your carbs-per-hour target for the duration you are training, hit it from early in the session rather than late, and train your gut to handle it the same way you train your legs.

This guide covers the actual numbers, the mechanism behind why the gut can absorb more carbohydrate than most athletes assume, how to build that capacity deliberately, the practical trade-offs between gels, chews, sports drink, and real food, and the failure modes that turn a good long session into a bad one.

The carbs-per-hour ladder

Carbohydrate needs scale with duration, not with how hard a session feels in the moment. The consensus ranges most sports nutrition researchers converge on:

• Under 60-75 minutes: no in-session carbohydrate needed. Glycogen stores cover this comfortably regardless of intensity.
• 1-2 hours: 30-60 g of carbohydrate per hour. This is the range that covers most weekend long runs and moderate rides.
• Over 2 hours: 60-90 g per hour, and in some well-trained athletes higher still, using a mix of glucose and fructose rather than glucose alone.

That last detail matters more than it sounds. The gut absorbs glucose and fructose through two separate transporter pathways. Glucose alone saturates its transporter at around 60 g per hour, so pushing more glucose through does nothing except sit in the stomach and cause discomfort. Fructose uses a different transporter, so pairing the two, typically in a 2:1 glucose to fructose ratio, opens a second channel and lifts total absorption capacity towards 90 g per hour or beyond. Most modern gels, chews, and mixed sports drinks are formulated with this ratio for exactly this reason, which is why product labels often list both maltodextrin and fructose rather than a single sugar source.

The gut is trainable, same as any other system

The ceiling on carbohydrate intake during long sessions is not fixed. It moves with practice, in the same way that lactate threshold or running economy move with training. Athletes who never feed intentionally during long sessions typically tolerate 30-40 g per hour before nausea or gut distress shows up. Athletes who train their gut deliberately routinely handle 80-90 g per hour with no issue, because gastric emptying rate and intestinal absorption both improve with repeated exposure.

Building that capacity takes one dedicated session a week, not every long session:

1. Pick one long run or ride each week as the designated gut-training session.
2. Start at whatever carbs-per-hour figure is currently comfortable, even if that is only 20-30 g.
3. Add roughly 10 g per hour every one to two weeks, provided the previous step landed without GI symptoms.
4. Hold at the new number for a week or two before adding again, rather than climbing every single session.

Six to eight weeks of this progression is usually enough to move a moderately trained gut from 30 g per hour to the 60-90 g range that longer races demand. It is slow, unglamorous work, and it is one of the few genuinely trainable variables in endurance nutrition that most athletes never bother to train.

Gels, chews, sports drink, and real food: picking the right format

None of these formats is objectively better. The right choice depends on the sport, the session length, and what your gut already tolerates.

• Gels. Concentrated, portable, precise carbohydrate dosing, usually 20-30 g per gel. Easy to take on the run without chewing, which is why they dominate running fuelling. The trade-off is a thick, sometimes cloying texture that some stomachs reject late in a session when gastric motility slows.
• Chews and blocks. Similar carbohydrate density to gels but taken in smaller, dosed pieces. Easier to titrate intake gradually and easier to fit into a jersey pocket for repeated small hits on a bike.
• Sports drink. Combines carbohydrate and fluid in one intake, which simplifies logistics on long sessions where carrying separate water and food is awkward. The limitation is that hitting 60-90 g per hour from drink alone can mean drinking more fluid than thirst or gastric comfort wants, particularly for smaller athletes.
• Real food. Bananas, rice cakes, dates, and similar options are cheaper, generally gentler on the gut, and psychologically easier to eat when a session has been going a long time and gels start to taste wrong. Chewing on the bike is trivial. Chewing while running at pace is genuinely harder, which is why runners lean more on gels and chews while cyclists mix in more real food.

Most long-session fuelling plans work best as a blend: a base of sports drink or gels for reliable carbs-per-hour dosing, with real food added for variety and gut relief on the longest days. Whatever the mix, rehearse it in training. Race day is not the place to discover a new product disagrees with you.

Pairing carbohydrate with fluid and sodium

Carbohydrate intake does not sit in isolation from fluid and electrolyte needs. A sports drink mixed too concentrated can slow gastric emptying and work against both goals at once. The detail on fluid volume, sweat rate, and sodium targets is covered properly in the hydration guide, which is worth reading alongside this one rather than repeating here. The short version for fuelling purposes: get the carbohydrate dose right first, then layer fluid and sodium around it rather than trying to solve all three from one bottle.

Common failure modes

Most long-session fuelling problems trace back to one of a small number of avoidable mistakes.

• Starting too late. Waiting until you feel low on energy means glycogen is already depleted and the deficit is playing catch-up rather than being prevented. Start carbohydrate intake in the first 30-45 minutes of any session that will run past the 60-75 minute threshold, well before you feel like you need it.
• Trying new products on race day. A gel, chew, or drink that has never been tested in training is a genuine risk, not a minor variable. GI distress under race stress and pace is common even with products that work fine in training, so anything untested at all is a real gamble.
• All fluid, no carbohydrate. Drinking plenty of water or an electrolyte mix with little or no sugar in it covers hydration but does nothing for glycogen. Athletes who bonk despite drinking regularly are almost always missing this distinction.
• Overcorrecting with too much, too fast. Jumping straight to 90 g per hour without gut training invites the exact GI symptoms that put athletes off in-session fuelling altogether. Build to it.

Worked example: a 3 hour ride and a 2.5 hour long run

3 hour ride, moderate intensity, temperate weather. Target 70-80 g of carbohydrate per hour once past the first 45 minutes. A practical breakdown: one bottle of 2:1 glucose:fructose sports drink providing roughly 40 g per hour, plus a gel every 40-45 minutes providing another 25-30 g, topped up with a banana or rice cakes around the two-hour mark for variety and gut relief. Total intake sits around 210-240 g of carbohydrate across the ride.

2.5 hour long run, race-pace long intervals included. Target 60-70 g per hour, slightly lower than the ride because running tolerates less gastric volume. A gel every 30-35 minutes from the 30 minute mark, each providing 25-30 g, supplemented with a few sips of sports drink between gels rather than large volumes at once. Chews work as an alternative to gels here if the texture is easier to manage at pace. Total intake sits around 150-175 g across the run.

Both examples assume a gut already trained to this range. An athlete newer to structured fuelling should start 20-30 g per hour below these figures and build towards them using the weekly progression described above.

How Pelaris fits in

The AI coach flags sessions that need a fuelling plan. A 30 minute recovery jog gets no prompt. A 3 hour ride or a long run past the 90 minute mark surfaces a carbs-per-hour target scaled to that specific session’s duration and intensity, rather than a blanket rule applied to every workout. This is built into how AI coaching reads the week ahead.

The Engine Room surfaces gut-training content on the days it matters. The Engine Room matches fuel content to your training phase, so a build block with a weekly long run or long ride on the calendar pulls up carbs-per-hour and gut-training guidance, while a taper week shifts towards different content entirely. You see what is relevant to the sessions actually coming up.

Race goals reshape the fuelling picture, not just the training. When a race goal is set, the weeks around it get restructured, taper before and recovery after, and that includes the sessions where gut-training and fuelling rehearsal matter most. Runners preparing a marathon can pair this guide with how to taper for a marathon and what to eat before a long run for the full arc from weekly long runs through to race morning. Hyrox athletes building towards a first event have a dedicated Hyrox race prep program with pacing and fuelling built around the format.

Logged sessions build the evidence for what worked. The workout tracker records duration, pace, and RPE per session, so a long run that fell apart in the last 20 minutes and one that finished strong are both on record. Over a training block within the endurance methodology, that history makes it obvious whether a fuelling change actually helped or just felt different.

The habit worth building

Treat carbohydrate intake during long sessions as a rehearsed skill, not an afterthought reached for when the legs start to fade. Set a carbs-per-hour target before you start, begin fuelling early rather than waiting to feel low, and use one long session a week to nudge your gut’s ceiling upward. The athletes who never bonk are not the ones with better willpower in the last 20 minutes. They are the ones who did the maths before the session started and trained their gut to handle the answer.