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Determining Hourly Carb Requirements: An Athlete’s Guide

Determining Hourly Carb Requirements: An Athlete’s Guide

To perform optimally in your next endurance training session or race, you need to consume a sufficient amount of carbohydrate to fuel your body. But how much is the right amount and how can you figure this out?

Despite the importance of these seemingly simple questions, it’s surprising how many athletes lack a clear picture of what their carb intake should be.

Different Types of Carbs vs. Different Amounts

We commonly see sports nutrition brands focusing on the carbohydrate source in their food or drink instead of how many carbohydrates in total the athlete will need. Every year there is hype around the newest and best carb source formulation.

You might have heard of some of these such as SuperStarch, cluster-dextrin and hydrogel technology to name a few. Each has its own different marketing angle in order to differentiate itself from its competitors in a very crowded marketplace. This is not to say that the type of carbohydrate in these products doesn’t matter at all, but what is far more important is delivering the correct amount of calories in the best form (drink, gel, bar etc) that suits the individual needs of the athlete’s activity.

The Importance of Carbs during Intense Activity

Glycogen provides the majority of the carbohydrate necessary to fuel the body during intense or prolonged periods of exercise. Glycogen is made up of chains of glucose molecules and is stored in the liver and muscles. However, your body’s glycogen stores get used up quickly during intense activity.

For example, 1½ or 2 hours of intense physical activity will typically deplete your stores enough to significantly compromise your performance.

So, at some point, taking in carbs (usually in the form of drinks, energy gels, bars or other carb-rich foods) is either helpful or necessary to maintain a high level of output for a long time.

What is Exogenous Fuel?

Carbohydrates that are ingested during physical activity are also called ‘exogenous’ fuel, meaning they come from outside of the body.

Because of the performance-enhancing potential it holds, the exact amount and type of exogenous fuel to consume has been the subject of much research and trial and error over the last few decades.

This is useful knowledge for athletes since we now have a set of definitive guidelines about how to determine your carb requirements to optimize performance during bouts of exercise of various durations and intensities.

How Many Carbs per Hour Do You Need?

Before looking at how many carbs per hour you will need, you need to consider a couple of other factors.

Assume you will begin your exercise with full glycogen stores, which means having consumed a carb-dense meal or snack 2-3 hours before the activity. If you aren’t starting with a full store of glycogen then you are likely to require more carbohydrate than otherwise recommended.

The following recommendations are based on fuelling for performance optimization, which means you want to push yourself hard for the duration. This is typical for competitive sports but might not apply easy training sessions or where your priority is something other than performance optimization.

For shorter periods and/or lower intensity exercise fewer exogenous carbohydrates are required.

Assuming the above, let’s look at how much carbohydrate you are likely to need:

Exercise Lasting Less than 60 Minutes

Most athletes won’t need to ingest carbs during an exercise period of less than one hour, since they should have sufficient glycogen stores to fuel the work. A carb-based snack or recovery meal after the activity is recommended to promote recovery, and is especially recommended if you plan to compete or train again a short time later.

Studies have shown pretty clearly that for an activity shorter than 30 minutes, ingesting carbs doesn’t make any significant difference to performance.

But for intense exercise lasting from 45 minutes to an hour, evidence suggests that performance might benefit from a carb mouth rinse or a small amount of carb ingestion. The mouth rinse can be convenient during an intense race when chewing and swallowing isn’t so easy.

A carb-rich drink will likely be the best choice for a hard, fast activity.

Exercise Lasting 1 to 2 Hours

The benefits of exogenous carbohydrate increase as duration increases. If your activity is going to last for between 1 and 2 hours, carbohydrate ingestion will almost certainly improve your performance. For exercise bouts lasting this long, the recommended intake is to consume 30 and 60 grams of simple carbs per hour. This works out as 1 or 2 energy gels or 0.5 to 1 liter of a typical isotonic (6% carbs approx.) energy drink per hour.

The longer the duration and the more intense the effort, the more likely it is you will need closer to 60 grams than 30 grams per hour. This especially applies to super-fit athletes who are physically able to sustain very high effort levels during their workouts.

Exercise Lasting More Than 2 Hours

If the activity lasts more than 2 hours, higher intakes of 60 to 90 grams of carbs per hour could be beneficial to elicit the best performance. 90 grams of carbohydrate per hour used to be considered the maximum recommended intake, however this is no longer a firm ceiling. In practice, it is not uncommon for elite athletes to consume 100+ grams per hour during races. For most of us though, this amount carbohydrate would not be tolerable, and it is recommended that athletes take time to build up to this rate of consumption, especially if they have been prone to suffering from GI issues in the past. Gradually tweaking your consumption upwards from your current tolerable limit during one or two hard sessions per week over 4-6 weeks seems to be the recommended approach to training your gut from those who have tried it successfully in the field.

Also, at this rate of carb consumption there may be some benefit in paying attention to the source of the carbohydrate ingested. This is where combined sources of carbohydrates such as glucose/fructose blends are often be preferred to help maximise the rate of absorption through the gut.

Does Body Size Affect Recommended Carb Intake?

Most people assume athletes with a larger body mass will need more carbs to fuel their higher energy output, but is this actually true?

Actually, the recommended amounts depend on grams per hour rather than grams per kilo or pound of bodyweight per hour.

The reason behind this is body mass is not especially relevant. The amount of carbs that muscles can utilize depends on how fast sugars are absorbed via the GI tract. Every athlete seems to absorb the carbs at a similar rate regardless of their weight or body size.

This means an athlete weighing in at 90 kilos and another who weighs 50 kilos would each require a similar amount of carbs per hour. This is because the determining factor in their respective fuel uptakes is how many carbs they can move through their GI system into their bloodstream, rather than their size or how much they weigh.

According to anecdotal evidence, athletes who have a lower body mass might even do better with a higher carb dose than heavier ones, since those weighing less have a higher relative contribution of exogenous carb oxidation to total energy expenditure.

However, it’s important to remember that every athlete is different. The correct amount of carbs per hour for the 90-kilo athlete in our above example might be less or more than the amount for the 50-kilo one. This is simply because no two people are the same and everyone’s body works slightly differently.

But overall it appears that body size is much less of an influential factor in setting carb intake rates than you would think.

What Do 30, 60 and 90 Grams of Carbs Look Like?

Every athlete has his or her preferred method of ingesting carbs. There are plenty of choices these days. In addition to isotonic drinks, there are chews, gels, bars, and of course real foods.

Each of these has its advantages and disadvantages, but suffice to say that as long as whatever you take agrees with your digestive system and works in a practical sense given the logistical constraints of your sport, there are few right or wrong answers.

A lot of the decision will come down to practicality. For example, if you’re running a marathon it’s easier to pop a few energy gels in your pocket than carry 4 energy drinks and 4 bananas around with you!

The most important thing is to ensure you determine the right amount of carbohydrate you will need per hour to ensure optimal performance. This, of course, is highly individual and can take some trial and error on your part to dial in.

Finally, let’s look at how much carbohydrate you will find in various types of energy products.

Each of the following carb counts is variable and approximate, depending on the brand, size and weight of the product.

  • Sports Energy Gels: 20 to 30g carbs
  • Sports Drink Mixes: 30g carbs per 500ml
  • Most Energy Bars: 40 to 60g carbs
  • Serving of Sports Chews: 20 to 30g carbs
  • Can of Coca Cola: 40g carbs
  • 4 Jelly Babies: 21g carbs
  • 1 Medium Banana: 25g carbs

Note: Bear in mind every brand has different amounts and types of carbs so check the packaging first.

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