If you’ve run a park run, half marathon, or are training for the upcoming Cape Town Marathon, you may know what it feels like to ‘hit the wall’ before the finish line. This includes fatigue, heavy legs, and a sudden dip in performance. To prevent this, a new study from Liverpool John Moores University and Science in Sport tested how much carbohydrate marathon runners can really handle. They also researched how runners can tailor their nutrition strategy to fuel smart and run fast.
“We recruited an elite cohort of male marathon runners, so these are guys with a personal best of 2 hours 30 or quicker,” explains Professor James Morton, chief science officer at SiS.
“We brought them into the lab after carbohydrate loading the day before. They consumed a high-carbohydrate breakfast as a pre-race meal. We asked them to exercise for two hours at an intensity that mimics race pace. This is important because a lot of studies have used recreational athletes and exercise intensities that don’t reflect race day abilities.”
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Even if you’re not an elite runner, these findings are useful. Practising a structured carbohydrate strategy in your training can help you metabolise fuel more effectively. This helps prevent hitting the wall, whether you’re tackling a 10 km park run or preparing for a long-distance race like the Comrades or Two Oceans Marathon.
The Methods
Eight elite male runners with an average PB of 2:22 completed treadmill runs at marathon pace. They did so while consuming 60, 90, or 120 grams of carbohydrate per hour in drink form.
Morton explains, “We used 60 grams per hour of a single source, which was maltodextrin. We also used 90 grams per hour of a dual-source blend, which was 60 grams of maltodextrin and 30 grams of fructose. Finally, 120 grams per hour was used, with 60 grams of maltodextrin and 60 grams of fructose.”
The aim was simple: “We wanted to look at the effects of carbohydrate consumption during running on how the body uses fuel. Runners often under fuel compared to other endurance athletes. We also wanted to monitor gastrointestinal distress at higher carb intakes.”
The Results
The researchers found that carbohydrate oxidation rose in a dose-dependent manner. At the highest intake, runners not only burned more carbs but also showed a 2.6% lower oxygen cost. This indicates improved running efficiency.
“In the 120 grams per hour trial, they were able to burn 1.5–1.7 grams per minute, some of the highest rates reported in literature,” says Morton.
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Even so, muscle and liver glycogen still play a role. During the two-hour runs, total carbohydrate use eventually declined. Thus, fuelling during exercise is crucial to maintain energy and pace. Traditional guidelines (last published in 2016) recommended 30–90 grams per hour depending on exercise duration. For races around 2.5 hours and above, a typical intake was 90 grams per hour of a dual-source blend (glucose plus fructose).
What This Means for You
‘If you really want to go fast, you probably want to have between 90 and 120g of carbs per hour’
For recreational runners preparing for a race, the key takeaways are:
- Carb-load the day before with foods like oats, maize meal porridge, bread, pasta, or rice.
- Eat a high-carb breakfast on race morning, such as toast with peanut butter and banana or a smoothie with oats and fruit.
- Practice during training. Experiment with carbohydrate drinks or gels on long runs so your stomach adjusts before race day.
- Use dual-source carbs (glucose plus fructose) to maximise absorption and minimise gut discomfort.
Even if you’re doing park runs or a half marathon, these strategies can help you maintain pace, avoid fatigue, and feel stronger in the final kilometres. Practising your fuelling strategy consistently ensures that your body knows how to use carbs efficiently. This helps you run faster and smarter.
This article by Kate Neudecker was published on Men’s Health UK – additional reporting and products added by the Men’s Health SA team.
