How To Perfect Your Fueling Plan

As you ride your bike, you burn calories. On top of that, you lose water and sodium when you sweat. If you are riding or racing for longer than one hour, developing an effective fueling plan will have a positive effect on your performance.

Darryl Griffiths, owner of Shotz Nutrition, taught us the basics of building a fueling plan on our podcast. This article will teach you how to develop your perfect plan.

Hydration: It All Starts With The Numbers

There are two important numbers you need to know when building a hydration plan. Your sweat rate, and the sodium concentration of your sweat. We wrote a detailed blog article on these values, and how you determine them. I'll summarize both values here.

Sweat Rate: The volume of sweat you produce in an hour. Measured in liters/hour. Your sweat rate changes with temperature and intensity. Heavy sweaters can lose up to 2.9 L of sweat per hour. That's nearly 3/4 of a gallon!

Sodium Concentration: This is how much sodium is in your sweat. This number is unique to you and differs between individuals. Your sodium concentration always remains the same even if you had extra salt on your French fries last night. Sodium loss is measured in mg/liter and ranges from 311 mg/liter to 3084 mg/liter.

These two numbers create a large combination of athletes. Written using the following relationship—sweat rate/sodium concentration—you can have athletes with, high/high, high/low, low/high, low/low ratios and anything in between.

Your specific ratio is usually an indicator of how well you perform in hot or cold weather.

Calculating Sodium Loss

Once you know your sweat rate and the sodium concentration of your sweat, calculating your sodium loss is pretty simple.

Sodium Loss = Sweat Rate X Sodium Concentration

Here's an example. Let's assume your race will take place in 90-degree heat and your sweat test in a 90-degree environment yields a 2.0 liter/hour sweat rate and a sodium concentration of 980 mg/liter. You will lose:

2.0 liters/hour X 980 mg/liter = 1960 mg of sodium/hour

Mission Impossible

All water, sodium, calories enter your body by being absorbed through the lining of your stomach. The total surface area of your stomach, and how efficient it is at absorption will determine the intake limits of your fueling plan.

Your skin is the largest organ in your body with an average surface area of 1.5 to 2 square meters (16.2 to 21.5 sq ft). Because the surface area of your skin is much larger than your stomach, you lose more water and sodium per hour than your stomach can absorb when heavily sweating.

Concerning calories, your body can burn well over 1000 calories per hour while racing. But, your stomach can only absorb about 350 calories per hour.

If you are racing in hot conditions, you will never entirely replace what you lose. Your goal is to develop a fueling plan that minimizes the loss.

The following chart lists the upper absorption limits of the human stomach. Keep in mind that these numbers represent a very efficient stomach, and your stomach may not be as efficient.

Item To Be Absorbed Upper Limit Of Absorption
Water 1.2 liters/hour
Sodium 2000 mg/hour
Calories 350 calories/hour

Separate Calories and Hydration

To build a customized fueling plan, you'll want to separate calories and hydration. Here's why.

Let's assume your stomach can digest the following quantities per hour.

Water: 0.9 liters
Sodium: 1100 mg
Calories: 300

How hard do you think it will be to find a sports drink that has this perfect ratio of water, sodium, and calories? If you guessed nearly impossible, you're right.

Let's assume you are the lucky one and Gatorade has the perfect mixture for you when racing in 90-degree heat. What happens when you race in 70-degree weather? You'll sweat less, which changes your requirement ratio, and your perfect mixture will no longer be perfect.

Separating calories and hydration allows you to customize your fueling plan for every race.


Your hydration plan can focus strictly on replacing water and sodium. Griffiths has created calorie-free sodium tablets that you add to water. The number of tablets you use will determine the sodium concentration of your drink. As long as you match the absorption limits of your stomach or the specific requirements for a race, you'll be in good shape.

It's important to remember not to overdo your sodium intake. If you have a low sodium concentration in your sweat, or you aren't sweating much, taking in too much sodium can hurt your performance.


With a hydration plan that contains no calories, your nutrition plan can focus on one thing, replacing calories. Griffiths recommends eating carbohydrates while exercising because they are the easiest to digest. Both protein and fats are hard to digest and can cause stomach upset.

Griffiths suggests using energy gels or real food with simple sugars to replace calories. Your stomach and your personal preference will determine what option works best.

Developing Your Plan

Once you've determined your hydration and nutrition needs for your specific event, your goal is to figure out exactly how many liters of water, mg of sodium, and calories you'll need.

When it comes to calories, you'll always be chasing a deficit while racing. Your goals is to eat as many calories as your stomach can digest.

Because your sweat rate is variable, your hydration plan will change based on the temperature. In cool weather, you won't be sweating much and your hydration plan may be able to keep up with your losses. In hot weather where you create a deficit, you'll want to maximize your fluid and sodium intake by finding the absorption limits of your stomach.

Unfortunately, there is no easy formula for figuring this out. Finding the limits of your stomach will take some trial and error. Griffiths recommends starting at the upper limit and adjusting down from there if you have problems. Remember, experiment while training, not racing.

Slow And Steady

To help improve the efficiency of your stomach, Griffiths recommends drip feeding—taking in small amounts of hydration and nutrition every 10 minutes. Drip feeding is much easier on your stomach and helps increase its efficiency. Taking in large volumes of fluid and nutrition at one time overwhelms your stomach and slows down absorption.

Will This Help Prevent Cramping

Griffiths says that 90% of athletes with cramping problems have high sweat rates or sodium concentrations in their sweat. If you are high on both scales, you're even more likely to experience cramping. The key to reducing cramping is to manage water and sodium loss to the best of your ability. A well-designed hydration plan is your biggest asset.

You're Not Done When You Get Home

Replenishing any water, sodium, or calorie shortage is critical for proper recovery. If you've completed a long ride or race in hot weather, there this a good chance you've created a water, sodium, or calorie deficit. Make sure you eliminate this deficit after your ride or race.

If you want even more information on this subject, listen to our podcast or pick up a copy of Griffiths' excellent book "Sweat. Think. Go Faster."

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