Carbohydrates for endurance: what to use, how much, and when

During endurance exercise, the body uses both fat and carbohydrate. As intensity rises, carbohydrate becomes more important because it can supply energy quickly. That is why the same athlete may tolerate a low-carb easy ride but struggle badly if a marathon, trail race, or long bike session is under-fueled.

The two practical concepts are glycogen and blood glucose. Glycogen is stored carbohydrate in muscle and liver. Blood glucose is the circulating fuel that helps keep intensity, coordination, and decision-making stable. Neither is unlimited. When the gap between what you burn and what you replace becomes too large, pace often fades before fitness is the only problem.

Carbohydrates are therefore not just a comfort detail. They are one of the main controls for holding useful intensity, reducing late-race drift, and keeping a plan executable when the event stops being easy.

For many endurance sessions, 30-60 g/h is a sensible starting range. It can cover steady rides, long runs, moderate trail sessions, or races where digestion and logistics are still the main constraints.

For longer events, higher intensity, or athletes already used to fueling, 60-90 g/h often becomes more relevant. This is common in marathon racing, long-distance cycling, triathlon, and longer trail events where small hourly gaps become large over time.

Some well-trained athletes can use 90-120 g/h, but that is an advanced target. It usually requires a tested mix of carbohydrate sources, regular intake, enough fluid, and gut training. It should be built progressively rather than attempted for the first time on race day.

At modest intakes, the exact carbohydrate blend may be less important than consistency. Once the target climbs, the blend starts to matter more. Maltodextrin is a common glucose-based source because it is easy to mix and can keep sweetness lower than table sugar at the same carbohydrate load.

Fructose can be useful alongside glucose or maltodextrin because it uses a different absorption route. In practice, this can make higher hourly carbohydrate targets more realistic for athletes who have trained the gut and tested the drink concentration.

The point is not to make every bottle complicated. The point is to match the carbohydrate target to the athlete, the event, and the drink volume. A 45 g/h plan can be simple. A 90 g/h plan needs more structure.

Gut training means rehearsing the intake that the race will demand. Start with a target you can already tolerate, then increase one variable at a time: more g/h, a different drink concentration, more frequent sips, or a different gel timing.

A simple progression could be 45 g/h for several long sessions, then 60 g/h, then 75 g/h if the event justifies it. The goal is not to force the stomach. The goal is to make intake routine while riding or running at realistic intensity.

Track more than the number. Note the fluid volume, weather, timing, texture, stomach comfort, and whether the plan still worked late in the session. Those details explain why the same 70 g/h can feel easy one day and too dense another day.

Long cycling session: a rider targeting 70 g/h might use one bottle per hour with 45 g carbohydrate plus one small gel or bar. If the weather is warm, the same carbohydrate target may require more fluid and a less concentrated bottle.

Trail race: a runner aiming for 50-70 g/h may split intake between soft flasks and gels because climbs, descents, and aid stations make drinking less regular. Sodium and fluid need to stay aligned with heat and sweat rate.

Marathon: a practical range is often 40-70 g/h depending on pace, duration, and gut tolerance. Faster or well-trained athletes may go higher, but only if they can drink or take gels at race pace without stomach disruption.

The first mistake is starting too late. Trying to rescue the final hour after under-fueling early often leads to rushed gels, stomach discomfort, and uneven pacing.

The second mistake is chasing a high target before the gut is ready. A 90 g/h plan is not better than a 60 g/h plan if it makes the bottle too dense or stops you from drinking regularly.

The third mistake is isolating carbohydrates from hydration and sodium. A drink can be correct in g/h but still fail if fluid volume, sodium concentration, or texture makes it hard to use.

Use this page to understand the carbohydrate lever. Then use the calculator to convert a target such as 45, 60, or 90 g/h into bottles, gels, and timing. That is where the plan becomes operational.

If the target relies on a bottle mix, read the hydration and sodium guides too. Fluid volume changes drink concentration, and sodium becomes more relevant when duration, heat, and sweat losses increase.

Once the numbers are clear, products are the final step: maltodextrin, fructose, sodium, bottles, soft flasks, and measuring tools should serve the plan rather than define it.