Fueling for Endurance Training

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Endurance exercise is generally any aerobic exercise performed for an hour or more, like running, swimming, and cycling. Think marathoner or triathlete. But whether you’re competing or not, if you’re performing this type of physical activity, it’s important to know the difference in fueling for this type of activity versus a strength-and-power or stop-and-go type sport.

Let’s break down the differences and talk about some key recommendations for optimizing endurance fueling.

Carbohydrate needs before and during exercise

When it comes to endurance exercise, while more fat is being burned as fuel relative to higher intensity, shorter duration exercise, carbohydrates are still the predominant source of fuel for endurance exercise. Our body converts carbohydrates eaten before exercise into energy, however the longer and harder training is, the more the body relies on glycogen to fuel it.

Glycogen is carbohydrate energy that is stored in the muscles and liver. As this stored energy is depleted, levels of perceived fatigue increase until you feel like you’ve hit a wall and physically can’t continue. This is referred to as “bonking”. Bonking means you’re out of glycogen, out of glucose.

How to avoid bonking? Eat enough carbs before and during endurance based exercise. For 1-2 hours of training aim for 30-60g of carbohydrate 30-60 minutes before exercise, and aim for an additional 30g of carbohydrate per hour.

Focus on low fiber, low fat, simple carbohydrate sources. Liquid, semi-solid, or solid food options all work here. You could use a specially formulated endurance drink, a gel, chews, an energy waffle, or real food options. Experiment with options during training and outside of competition to find what works best for you without causing stomach upset.

If training for 2-3 hours, shoot for at least 60g of carbohydrate before exercise and then an additional 60g of carbohydrate per hour. For endurance exercise longer than 3 hours, 90g of carbohydrate per hour is most optimal and you’ll want to look for options that provide both glucose and fructose to maximize absorption.

Consuming and tolerating that much carbohydrate during training can take some time to train and adapt your gut. Build up to it incrementally. If you’re training for a competition, start working on this several weeks to months out and have your fueling strategy nailed well in advance.

What about carb loading?

Carb loading is a strategy that has been shown to improve stamina and performance for endurance events by as much as 20%. With carb loading you are attempting to supersaturate glycogen stores. It’s typically only recommended for events that will be longer than 90 minutes and that are performed at a moderate intensity level or greater. So if you’re running a 5k, 10k or half marathon or if you’re walking or jogging at a lower intensity level, this is not necessary and can actually be counterproductive.

For every 1g of glycogen stored, you store 2-3 grams of water. For shorter duration or lower intensity exercise this could weigh and slow you down.

If you are competing or training for a longer event where carb loading might be applicable, aim for 10-12g or carb per kilogram of body weight. This would be consumed 24-36 hours before the event. Again, it takes time to be able to adapt the body to be able to appropriately tolerate and utilize this much carbohydrate. Additionally, the amount of glycogen your body can store will vary person to person. The more muscle, the more glycogen your body is capable of storing.

Lastly, let’s cover some nutrients and supplements potentially helpful for endurance training:

Beetroot juice taken 1-2 hours before endurance exercise can help reduce oxygen cost during exercise, potentially improving stamina and endurance. There are various supplemental forms of beetroot available that may be worth experimenting with.

Tart cherry juice can be beneficial for promoting muscle recovery and reducing inflammation and soreness. Most studies see a benefit at 8-12 oz or a 1-2 oz concentrate consumed twice a day.

Caffeine supplementation may also be helpful for sustaining endurance, however not everyone will respond to caffeine the same way and high amounts of caffeine may cause GI distress, so start with a low amount and see how you tolerate it.