In my last blog post, I talked about how maintaining hydration is critical for delaying fatigue and that dehydration is often perceived as bonking, leading to ingestion of liquid calories, which further inhibits hydration. That said, ingesting calories is important to endurance performance.

Hydration is King, but Fueling is Important too….

The question that always arises: “how much carbohydrate can I use/do I need per hour of exercise?” A.k.a “how can I increase my carbohydrate intake to delay my fatigue? 

Let’s all return to the fundamental reason we need carbohydrate during exercise: to delay fatigue.

Depletion of carbohydrate is considered one of the primary causes of fatigue during exercise that is sustained for long periods of time. But the most critical cause of fatigue is a drop in total body water and subsequent blood volume loss, as described in our blog on bonking vs dehydration. The average adult male has 300-500g of glycogen stored in the muscles and another 75-100g stored in the liver. This is enough carbohydrate to run at moderate intensity for about 20 miles. The main objective of supplementing with carbohydrate during prolonged, strenuous exercise is to maintain blood glucose concentrations. But how much is the question?

This is where it gets confusing. Many brands that sell calorie-rich “fuel” spend a lot of money marketing (often contradictory) misinformation. This leaves athletes confused. Real science provides some concrete answers to the fueling questions, so let’s talk science.

But before we do, let me give a simple “rule of thumb” that all athletes should follow: Food in your pocket, hydration in your bottle. And by food, we mean the kind you can chew; not the kind you drink or slurp. (Gels are a no-no). (See our blog post on the food in the pocket, defined).

We know that the ingestion of carbohydrate during prolonged, moderate intensity exercise helps prevent the decline in blood glucose and spares glycogen. When muscle glycogen stores are low – i.e. with two a day sessions or inadequate recovery – the average 150lb male can reach maximum oxidation rates of 1.0-1.2 grams of carbohydrate per minute, or 60-72 grams/hour (note: a combination of two sugars allows this maximal rate to be achieved). Whether increasing this oxidation rate improves endurance performance has yet to be determined. Recent research has indicated a curvilinear response to carbohydrate oxidation, indicating ~78 grams per hour can optimize performance. The caveat here: the participants in this study were all similarly (elite) trained males, aged ~28 years, and the results were based on sample size of 13 (n=13), which is not very translatable to the overall athletic population.

So what does this mean? Fitness status, training history, age, sex, intensity, pre-exercise nutritional status all impact the amount of carbohydrate needed to delay fatigue. Regardless, the amount of exogenous carbohydrate required for best results is 30-60 gram per hour.

Going with the 30-60 grams of carbohydrate per hour, let’s go back to our typical 5-8% carbohydrate solution sports drink.  Per serving (8oz), you would expect ~12-19 grams of carbohydrate. One 16oz bottle of this sports drink will give you the minimum amount of carbohydrate needed.  When you top this off with a gel (~27-30g carbohydrate), you quickly approach the maximum your body can oxidize.

The current mantra of sports nutrition and the overwhelming amount of marketing messages indicate that eating and consuming calories is going to improve your performance and delay fatigue: i.e., “the more the better.” So it is very common for athletes to overeat during training and racing, with the thought that they are supplying their muscles with needed carbohydrate. But what really happens? You’re ingesting too much, so the excess will remain in the stomach or intestinal tract too long, causing nausea, pain, and discomfort (which of course, impairs performance).

The solution to delaying fatigue does not lie in consuming excess calories; it lies in attacking the two primary problems of fatigue: reducing the loss of blood volume – using a drink that hydrates; and topping off body with small amounts of carbohydrate – mixed types are best. (see our blog post on the types of food to eat).


How to do this? Hydration in the bottle, food in the pocket! It starts with recovery, and moves to fueling well at least 3-4 hours before you head out training/racing.  Across the board stay on top of your fluid losses  – drink Osmo Active!, and when it comes to fueling, make a mental note of environmental conditions, intensity, when you last ate, and if you really need the top end of the carbohydrate range.  Remember, the fatigue towards the end of a session or race is rarely due to hypoglycemia, and most likely attributed to dehydration!