Carbohydrate is the primary fuel source for high-intensity endurance exercise. Your body stores carbohydrates as glycogen in your muscles and liver — think of it as your current account for energy, with fat being more like a savings account. The problem? That current account has a limited balance. After roughly 90–120 minutes of hard effort, glycogen stores are significantly depleted, and performance drops noticeably.
That's why taking in carbohydrates during exercise — in the form of gels, chews, bars or drinks — is not just helpful but essential for anyone training or competing at high intensity over longer durations.
The sports nutrition market tends to fixate on the type of carbohydrate in a product — hydrogel technology, cluster dextrin, fructose-to-glucose ratios — but this is secondary. What matters most, and what is most often overlooked, is getting the right total amount of carbohydrates per hour into your body. Here are the evidence-based guidelines:
Under 1 hour
If you start well-fuelled (i.e. with a carb-rich meal or snack 2–3 hours before), your glycogen stores will cover most efforts under an hour without any additional carbohydrate intake. For very short durations (under 30 minutes), carbohydrate ingestion has essentially no measurable impact on performance. That said, for intense all-out efforts of 45–60 minutes, a small carbohydrate intake or even a carb mouth rinse — swilling a sugary drink without swallowing — can provide a modest performance benefit by stimulating receptors in the mouth and brain.
1–2 hours
As duration increases, the benefits of fuelling become increasingly significant. For efforts in this range, aim for 30–60g of carbohydrates per hour. In practical terms, that's roughly 1–2 standard energy gels or 500ml–1L of an isotonic sports drink (around 6% carbohydrate concentration). The harder and longer within this bracket, the more you should push toward the upper end of 60g/hr — particularly if you are well-trained and capable of sustaining a high workload.
2 hours and beyond
Once you pass the two-hour mark, higher carbohydrate intakes have a clear dose-response relationship with performance: more carbs, better results — up to a point. Target 60–90g of carbohydrates per hour. At this level, the composition of your carbohydrate source becomes more relevant. Using a glucose/fructose blend (known as multiple transportable carbohydrates, or MTCs) allows the gut to absorb larger quantities by using different intestinal transport pathways simultaneously, reducing the risk of GI distress.
90g/hr was long considered the practical ceiling for carbohydrate absorption. However, there is growing evidence from elite endurance sport — Tour de France riders, IRONMAN podium finishers — that some athletes regularly consume more than this. For most recreational athletes, even reaching 90g/hr represents a significant step up and requires deliberate gut training.
Ultra-endurance (6 hours+)
For very long efforts, simple carbs-per-hour logic is no longer sufficient on its own. Taste fatigue, digestive load and the need for some protein and fat from real foods all become relevant. Fuelling ultras is a topic in its own right.
Does body weight matter?
Surprisingly little. Carbohydrate absorption is primarily limited by intestinal transport capacity, which is roughly similar in all athletes regardless of body size. A 55kg cyclist and a 85kg triathlete will benefit from roughly the same carb intake per hour.
Practical takeaway
Most recreational athletes significantly undereat during training and racing. If the numbers above seem high compared to your current habits, that is a sign there is real performance improvement available to you. Start by identifying your current tolerable intake, then gradually increase by 10–15g per hour over 4–6 weeks of targeted gut training. Your body will adapt.
