Why Carbs Matter During Exercise (And How Much)

Why carbs matter during exercise (and how much you actually need)

18th July 2026 Nutrition

Carbohydrates have a PR problem. Avoid them for fat loss, the internet says. Cut them for longevity. Cut them, full stop. And in some contexts, that's a reasonable take. But the moment you go past 60-90 minutes of moderate-to-high intensity exercise, the conversation changes completely.

Performance stops being a willpower question and starts being a fuel question. The International Society of Sports Nutrition recommends 30-60g of carbohydrate per hour for endurance work lasting over 60 minutes (Jeukendrup, Sports Medicine 2014). Below that, you're cooked. Not metaphorically, biochemically.

Key takeaways from this blog:

Muscle glycogen runs out in 60-90 minutes of continuous activity. Once it drops, output drops with it (Jeukendrup, 2014). You can't motivate your way around an empty fuel tank.
Single-source glucose absorption tops out at ~60g per hour, limited by the SGLT1 transporter in the gut. More glucose alone doesn't mean more energy delivered. Just more GI distress.
Mixing carb sources (glucose + fructose) opens a second absorption pathway via GLUT5, lifting absorption to 90g+ per hour (Jeukendrup, 2014).
Dual-source carbs measurably improve endurance performance vs single-source (Currell & Jeukendrup, Medicine & Science in Sports & Exercise, 2008).
Endure is a tri-carb blend designed to mix with Hydrate. 25g of carbs per scoop. Built for sessions over 60 minutes, not for everyday hydration.

The thing nobody tells you about willpower
What's actually limiting you mid-session
Why glycogen runs out faster than you think
Carbohydrate absorption has a ceiling
Why mixed carb sources are a game change
Where most people get fuelling wrong
How fuel and hydration work together
How Awesome Endure is built
FAQ

1. The thing nobody tells you about willpower

Here's the test I want you to run mentally. What would happen if you went into a 90-minute session having only had water in the previous 4 hours? What would happen if you tried to push through the last 30 minutes of that session on grit alone? What would happen if you did that twice a week for a month?

If you've trained for any length of time, you know the answer. You hit a wall. Pace drops. Power drops. Effort feels like wading through wet concrete. And you blame yourself, your sleep, your recovery, your motivation.

Sometimes that's right. More often, it's a fuel problem with a willpower label slapped on it.

2. What's actually limiting you mid-session

Let's level with each other about what happens in a long session.

In the first 30-45 minutes, your body's running on a mix of stored carbohydrate (muscle glycogen) and fat. You feel good. Effort matches output.

Somewhere between 45-90 minutes in, depending on how hard you're pushing, glycogen stores start to deplete. At first, you don't notice. Then perceived exertion creeps up at the same workload. The same pace feels harder. You drop your power output without consciously deciding to.

This isn't a mental shift. It's a physiological one. Your nervous system pulls back to protect blood glucose, and that protection feels like a slow-motion shut-down.

Pushing through doesn't work past a certain point. Once fuel availability becomes the limiter, no amount of mental override compensates for falling blood glucose. That's the "hitting the wall" feeling endurance athletes describe.

3. Why glycogen runs out faster than you think

Glycogen is the stored form of carbohydrate in muscle and liver. It's your body's most accessible fuel for moderate-to-high intensity work. Sprints, intervals, sustained efforts, repeated high outputs. All of it pulls from glycogen first.

The problem: stores are limited. Even in well-fed individuals, glycogen depletion starts within 60-90 minutes of continuous activity, and sooner if intensity is high or efforts are repeated. Once availability falls, fatigue rises, power output declines, and perceived effort climbs.

Which is why fuelling becomes relevant for endurance training in a way it isn't for short sessions. A 45-minute lifting session? You don't need intra-workout carbs. A 90-minute bike ride at threshold? Different story.

4. Carbohydrate absorption has a ceiling

Here's the part most people don't know, and it's important. Your body can't just absorb unlimited carbs.

Glucose is absorbed through a transporter called SGLT1, which saturates at around 60g per hour. Pour more glucose into your gut and it doesn't get absorbed faster. It sits there, draws water in, and creates the classic GI distress problem endurance athletes know well. Stomach cramps, urgency, the works.

That's why simply taking more carbs isn't the answer. You hit a transport ceiling, and the extra ends up working against you instead of for you.

5. Why mixed carb sources are a game change

This is where the research gets interesting. Combine different carbohydrate sources, typically glucose and fructose, and you open up multiple transport pathways in the gut.

Glucose uses SGLT1.
Fructose uses GLUT5.

Two different doors. Two separate flow rates. Total absorption climbs to around 90g per hour or more, depending on the ratio. This is what sports nutrition calls multiple transportable carbohydrates, and it's one of the biggest practical advances in endurance fuelling in the past 20 years.

The performance impact is measurable. Currell and Jeukendrup's 2008 trial in Medicine & Science in Sports & Exercise found cyclists performed an 8% time-trial improvement on a glucose-fructose blend compared to glucose alone, with no difference in GI distress. Same total carb intake. Different blend. Better performance.

6. Where most people get fuelling wrong

Two common failure modes show up again and again.

Failure mode 1: skip carbs entirely. Common in people who do long sessions on the back of a low-carb diet, or who fuel only with water and expect that to be enough. The result is earlier fatigue, lower output, longer recovery, and a slow erosion of training quality. The session you do depleted is rarely the session that progresses you.

Failure mode 2: high-sugar, single-source drinks. Lucozade, sweets, gels with just glucose. They deliver carbs but cap out at the SGLT1 ceiling. Past that, the body can't absorb it, and what's left causes GI issues. The added problem: high sweetness gets harder to tolerate hour after hour. "Taste fatigue" is real and it ends sessions early.

Neither approach gets the science right. One under-fuels, the other over-fuels in a way the gut can't process.

7. How fuel and hydration work together

Carbohydrates don't just fuel performance. They also help drive fluid absorption.

Fluid uptake in the gut is influenced by both sodium and glucose, via that same SGLT1 transporter.

This is why clinical rehydration solutions use a sodium-glucose combination, and it's why carbohydrate-electrolyte sports drinks are absorbed faster than plain water during exercise.

Practically, this means fuel and hydration aren't separate problems. A well-built fuelling strategy supports hydration. A well-built hydration strategy needs a small amount of glucose to drive absorption properly. They belong together.

Which is why Endure was built to mix with Hydrate, not to replace it.

8. How Awesome Endure is built

Endure isn't a daily product. It's a tool for specific situations, used in combination with Hydrate.

The basics:

Tri-carb blend (three different carbohydrate sources, designed to use multiple absorption pathways)
25g of carbohydrate per scoop (40ml)
Flavourless but slightly sweet (mixes with any Hydrate flavour without clashing)
No electrolytes (those come from Hydrate, deliberately separated so you can dose each independently)

Practical use:

Sessions over 60 minutes at low-to-moderate intensity: 1 scoop Endure + 1 scoop Hydrate per hour
High-intensity sessions over 60 minutes: 2 scoops Endure + 1 scoop Hydrate per hour
Don't bother for short sessions. Hydrate alone covers them.

£11 for 16 servings, so about 69p per session. Cheaper than a gel, and the dual-pathway absorption means more usable energy with less stomach drama.

Shop Awesome Endure

FAQ

Do I need carbs for a 45-minute workout?

Probably not. For sessions under 60 minutes, your existing muscle glycogen has you covered, particularly if you've eaten reasonably in the previous few hours. Intra-workout carbs become relevant past the 60-90 minute mark, or in high-intensity repeated efforts where glycogen demand spikes. For a normal 45-minute session, focus on being well-fuelled going in (a proper meal 2-3 hours before, or a smaller snack 30-60 minutes before).

Will carbs during training stop me losing fat?

Honest answer: probably not, if you're sensible about it. Body composition is driven by total daily energy balance, not by whether you had 25g of carbs during a long session. If you're doing 90-minute sessions and you skip fuel to "save calories," the bigger risk is that you train below your capacity and accumulate less work, which slows progress in everything. Eat to support the work. Manage the daily calorie budget around it.

Can I just use a gel?

You can. Gels deliver carbs in a concentrated dose and are useful in race contexts. The downsides: they're more expensive per gram of carb, they often use single-source glucose (so they hit the SGLT1 ceiling faster), and the high concentration can cause GI issues unless taken with adequate water. A powder mixed with Hydrate gives you carbs, fluid and electrolytes in one drink. Personal preference, but the powder approach is more practical for long sessions.

How much carb should I actually take per hour?

Depends on duration and intensity. The ISSN recommends 30-60g per hour for endurance exercise over 60 minutes. Lower end for shorter or less intense sessions. Higher end (up to 90g per hour using dual-source carbs) for longer or more intense work. As a rough guide: 60 min steady, 30g. 90 min steady, 45-60g per hour. 2+ hours intense, 60-90g per hour.

Will I get a sugar crash after using Endure?

Unlikely if you're actively training. Insulin response is significantly blunted during exercise because muscle contractions move glucose into cells through a different pathway (GLUT4 translocation) that doesn't require the usual insulin signal. So intra-workout carbs don't produce the same crash you'd get from sugar at rest. Post-workout, normal rules apply, eat a proper meal.

Can I take Endure outside of training?

Technically yes, but it's not designed for that. Outside of training, your body doesn't need rapid fuel delivery, so a regular meal will do the job better. Endure is built for the absorption challenge of training, not for daily nutrition.

What to do with this

Most people overcomplicate fuelling. The actual logic is simple. For sessions under an hour, eat normally and don't overthink it. For sessions over an hour, especially if they're intense, you need carbs in. The exact strategy depends on duration, intensity, and what you can tolerate. Try a dual-source carb drink for two weeks of long sessions and pay attention to how the back half of your sessions feels. If output holds up better than before, you've found something.