Do you really have to fuel that workout? Depends on your goals.
Endurance and high-intensity exercise require fuel to be sustainable, and there's only so much stored, readily available energy we can use before fatigue sets in and your performance declines.
However, how much carbohydrates you need per hour depends on a few factors, including exercise duration, intensity, performance goals, and your weight.
Let's take a look at these different components to help you figure out how best to fuel your training.
Why fuel with carbohydrates?
Carbohydrates are King when it comes to the fuels you choose, especially for high-intensity intermittent exercise and prolonged endurance.
This macro is the preferred energy substrate of muscles and your brain.
Endogenous carbohydrate stores
In most sports, the point of fatigue is closely linked to glycogen depletion in the exercising muscle.
We simply cannot store enough carbohydrates within the body to sustain a decent pace for much longer than 90-120 minutes.
This is because our endogenous (*in the body) carbohydrate stores called glycogen, found in our liver and muscles, can only store about 500 to 600 grams of carbohydrates when absolutely maxed out.
The higher the intensity, the faster you burn through your glycogen stores.
Exogenous fuel sources
Using sports fuels that contain carbohydrates during training and races, called exogenous fuels, helps you preserve these glycogen stores and allows a much longer time to exhaustion.
These exogenous fuels are used preferentially, helping to spare glycogen stores by being used first. You won’t spare all your glycogen, both endo- and exo-sources of fuel will be used concomitantly, but your stored glycogen form will last much longer.
The bottom line is that taking in carbohydrate-rich sports fuels will help you maintain that higher pace for much longer.
*Want to know more about low-carb training and racing and if it can improve your performance? Check out this article.
How much carbohydrates do you need per hour?
If you're a recreational athlete exercising for less than an hour, you probably don't need to fuel your workout except with water and perhaps some electrolytes if it's hot.
Honestly, if you're just out there having fun and not training for anything, you may not need much fuel for exercise lasting under 2 hours. However, hydration is critical for being active for over one hour.
If you're training for a specific event that will last longer than an hour, and you want to do well, then you've got some fueling to do.
Under 30 minutes
Nothing needed. Not even water has been shown to provide benefits for a workout under 30 minutes.
45 to 75 minutes
This is a grey area. Most people may not need much, if any, fueling. However, if you are doing an 'all-out' workout, you'll benefit from some carbohydrates.
Since this is a fast, down-and-dirty workout, a sports drink may work best. Both carbohydrates and electrolytes will be easily and quickly absorbed and utilized.
Don't wait too long to start fueling. Early and often is key to making the most of these exogenous fuels.
1 to 2 hours
Research indicates that about 30 grams per hour is likely sufficient for this time frame.
2 to 3 hours
Increasing to about 60 grams per hour will help your body meet its increasing energy needs.
3+ hours
Now you're getting into the deep stuff. Research shows that 90 grams per hour may be best for these longer-duration training sessions.
I've even had Ironman athletes get up to 120 grams per hour on the bike to meet their needs.
Other factors that impact your carb needs
If you just want to 'make it through' the race, stick with the above guidelines.
If you really want to optimize your performance, it's important to account for other factors.
Your size
Height and weight play a role in how much carbohydrates are needed to support your activity.
Generally, if you are taller or heavier, you'll need more carbs per hour to fuel your work. Likewise, if you're on the smaller side, you may need less.
Your performance goals
Are you in it to win it or just to finish?
If you'll be maintaining a steady state at a moderate pace, then you may not use carbs as quickly as someone who will be intermittently sprinting, hill climbing, and pushing themselves to their limits for long periods.
The faster and harder you push, the more carbs you'll need to support this effort.
Whether you carb-loaded or not
If you'll be out there for longer than 3 hours, carb loading helps top off your glycogen stores so that you can perform longer without hitting the wall.
If you go out there with very little carbs already in the tank, then you'll have to rely more heavily on exogenous fuels.
Carb loading may look like a carbohydrate-dense meal 3 hours before you start training, or it could be multiple meals focused on carbohydrates to help prepare for a long-duration race.
The type of carbohydrate matters
The type of carbohydrates consumed makes a big difference as well. Each type of sugar (glucose, fructose, maltodextrin) is broken down and absorbed via a different pathway in the intestines.
So if you take in too much of one type, the pathway gets overwhelmed and the rest of the sugar will just… find its way out. GI distress anyone?
Studies show that your body cannot take in more than 60 grams of one type of carbohydrate per hour.
Taking in a mixture of sugars is best since more will be absorbed. Interestingly, fructose takes much longer to digest and absorb, so drinking juice or other pure fructose-sweetened beverages may lead to stomach upset and other GI issues.
Look for a sports fuel with glucose or maltodextrin first, then fructose, to help with better digestion.
Using multiple types of fuels will also help you get a variety of carbohydrate sources. Consider using a sports drink, gels, and chews depending on your preference.
Ingredients to watch out for
Not all sports fuels are created equal.
Here are specific ingredients to avoid or minimize:
Artificial sweeteners may cause GI distress for many athletes.
Excessive amounts of added vitamins and minerals, such as added vitamins C and E, are generally unnecessary and may lead to gut issues.
Avoid fat, fiber, and too much protein during endurance events and training. These take a long time to digest and often sit in your stomach like a rock causing bloating and discomfort. Remember: Carbs are king! Fat and protein are better used in lower intensity, long duration exercise such as hiking, and walking. A little bit is okay when cycling, too.
Bottom line
If you're going to fuel, don't wait until you're hungry. Studies show that by this time, it may be too late. Get started early and take in your sports fuels in evenly spaced intervals (ie: every 30 minutes or every 45 minutes, etc.).
If you're using a sports drink, sip early and often. Take sips every 5 to 10 minutes to help meet your hourly needs. Don't gulp or drink too much at one time! This can lead to GI distress.
And finally: Train your gut!
Don't expect to go out there on race day and fuel according to a plan you've never tried. Training your gut means acclimating it to the amount of carbohydrates and fluids per hour you need.
You may need to slowly increase to the desired amounts as you train your gut to digest these volumes. Be sure to train with your fueling plan weekly for at least 2 months leading up to your race.
Get out there!
Sources:
Jeukendrup, A. E. Nutrition for endurance sports: marathon, triathlon, and road cycling." J Sports Sci 29 Suppl 1: S91-99, 2011.
Jeukendrup, A. (2014). A step towards personalized sports nutrition: carbohydrate intake during exercise." Sports Med 44 Suppl 1: 25-33, 2014.
Murray B, Rosenbloom C. Fundamentals of glycogen metabolism for coaches and athletes. Nutr Rev. 2018;76(4):243-259. doi:10.1093/nutrit/nuy001
Vandenbogaerde TJ, Hopkins WG. Effects of acute carbohydrate supplementation on endurance performance: a meta-analysis. Sports Med. 2011 Sep 1;41(9):773-92
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