USA Triathlon News Blogs Fuel Station Avoid the Bonk: How ...

Avoid the Bonk: How to Properly Fuel During a Race

By John Hansen | Oct. 02, 2018, 11:11 a.m. (ET)

Nutrition in racing

Executing a successful nutrition and hydration plan during your workouts is one key element to successful training. When considering nutrition and hydration during a workout and race, it is important not only to choose the right protocol to provide you energy and maintain your fluid levels, but to also minimize GI issues, which is particularly true of the long course triathletes who often train for three-plus hours. 

The following information is to be used as a guideline to develop better fueling and hydration practices during your longer (75-plus minutes) training sessions and races. Long course triathletes should pay particular attention to these guidelines, as many of your workouts last for several hours.  

The following are the goals for fueling and hydration during a training session or race: 

  • To provide the body a more immediate energy source to sustain your efforts
  • Maintain blood sugar levels
  • Delay depletion of stored glucose (carbohydrates)
  • Prevent dehydration

To begin, there are three pillars when it comes to any protocol.  

First, you should begin intake of food and fluids within the first 30 minutes of the start of the workout/race (long course racing is the exception). If you wait over 90 minutes, you will already be behind in your fueling and hydration, and it will be difficult to catch up, leading to a sub-par effort. So, for long course athletes, fueling and hydrating in T1 or the very start of the bike is important.

Second, you will typically drink and eat every 15-30 minutes during longer workouts or races. 

Third, whenever you eat a solid or semi-soft product you need to “chase” it down with water to help with digestion and absorption.  


The duration and intensity of the workout/race are two of the key determinants in creating the right fueling protocol. Use the following guidelines to help you choose the right protocol for your particular workout/race:

  • Three-plus hours, steady to moderate effort: up to 90 grams of carbohydrates or up to 360 calories per hour 
  • Two to three hours, steady to hard effort: 30-60 grams of carbohydrates or 120-240 calories per hour 
  • 75 minutes to two hours, moderate-hard to hard effort: 30-40 grams of carbohydrates or 120-160 calories per hour 
  • 75 minutes to two hours, steady to moderate effort: 30 grams of carbohydrates or 90 calories per hour 
  • Less than 75 minutes: water only (if your workout is occurring after an extended fast sleep or is an afternoon workout without any lunch, then 30 grams of carbohydrates or 90 calories maybe be necessary)

These consumption values and time frames can vary in the recommended ranges depending on personal food tolerance, individual experience and how much you have eaten throughout the workout. For example, you may find it is better to eat more solid or semi-solid food in the beginning and middle of the long workout and more semi-soft and liquid food toward the end of the long workout, especially if it is a run and/or it is in warmer and more humid climates. 

The predominant source of calories during workouts and races comes from carbohydrates, with the option of having a small amount of protein and fat. Carbohydrates should be a mix of simple sugars such as fructose and/or glucose and a more complex sugar such as maltodextrin and/or sucrose (check your ingredients list). The body has several receptors for different types of sugars so having a mix of sugars optimizes the utilizations of carbohydrates in the body.   

Traditional solid sources include bars, wafers and bananas. Semi-soft sources include gelatin blocks or gels. Non-traditional sport foods can also supplement packaged sources and include dried fruit, pretzels, saltines, crackers and even cooked potatoes. One of my favorite non-traditional foods is fig bars. They are a great way to get a lot of calories in a small package and are generally well tolerated by the stomach.

Triathletes should also assess how they feel and perform using their protocol, adjusting food/hydration choices, the amount and timing as needed. For instance, if you are getting GI distress from your bar, try a different bar with less fat and/or protein or use a semi-soft product.


Heat, humidity and sweat rate are the three key determinants in creating the right hydration protocol. To determine the appropriate amount of fluid to replace, weigh yourself at different fitness levels for several types of workouts and in different weather conditions prior to the workout, then weigh yourself after the workout to calculate sweat loss, accounting for fluid intake during the workout. (Fitness levels affect sweat rate. Less fit equals less sweat and vice versa). This is the fluid level you should try to replace during workouts under those conditions.  

However, if you do not regularly replace this volume of fluid during workouts, the key is to not let your fluid loss be greater than 2 percent of your body weight. Below 2 percent, your workouts will be far less productive, and you may experience health issues if it falls well below 2 percent.  

Using the general guideline of 12-28 ounces per hour, see below for specific workout/race recommendations given the sweat rates noted below and drinking every 15- 20 minutes:

  • Light sweat rate: drink 3-4 ounces
  • Moderate sweat rate: drink 5-6 ounces
  • Heavy sweat rate: drink 7-8 ounces

Variations to these hydration recommendations may be needed if the workout is a run and you don’t tolerate these levels of fluid in the gut or if it is hot and or humid which means these fluid intake levels should be at the top of the range.

Of course, fluid intake comes in form of water and/or a carbohydrate sports drinks. When determining your calorie intake, if you drink a carbohydrate drink then the calories need to be accounted for in your total calorie needs. My recommendation is that 50 percent of your hydration should come from water and 50 percent from a carbohydrate sports drink.

I recommend 50 percent of your calories come from a sports drink because it aids in getting your electrolyte (sodium, potassium, calcium and magnesium) intake levels addressed, supplementing what you get from bars and/or gels. There are also stand-alone electrolyte tablets and pills you can take, if your food and fluid sources do not provide enough electrolytes.

The primary electrolyte you are concerned with is sodium, so use the following guidelines to help you chose the right protocol for you and your particular workout given the sweat rates below and the noted weather conditions:

  • Light: 500 milligrams/liter
  • Moderate: 600 milligrams/liter
  • Heavy: 700 milligrams/liter

Lessen your intake by 100-200 milligrams for cool dry conditions and increase your intake by 100-200 milligrams for hot, humid conditions.
Fluid and electrolyte intake are critical aspects of training since there are some serious health issues that can occur if you do not consume enough electrolytes, hydrate enough or even hydrate too much (only drink water). 

Proper fueling and hydrating is essential to a quality workout/race and by applying the above information into your daily workouts, you will take additional steps toward optimizing your abilities as a triathlete. 

John Hansen, USAT, and USA Swimming Level 1 Coach and USA Cycling Level 3 Certified coach, Folsom California, with 23 years of coaching experience. Hansen has an MS in Exercise Physiology and previously worked at the UC Davis Sports performance lab for five years. Hansen has coached athletes from beginner to pro level, competing at many major US Age Group National Championships and World Championships, as well as the US Men's Pro championships. Hansen currently coaches the UC Davis Collegiate Club Triathlon team with multiple teams placing in the top 12 and several athletes placing in the  top 20, in the past eight years at the Collegiate Club National championships. Hansen also has his own coaching business, primarily coaching long course athletes, 70.3 and 140.6. Visit or email


Academy of Nutrition and Dietetics, Powers & Howley, Exercise Physiology, Theory and Application to Fitness and Performance,  1994

Medicine & Science in Sports & Exercise. 48(3):543-568, March 2016.

USAT – Level 1 Coaching Manual Nutrition Science for the Multisport Athlete, Jennifer Hutchins and Sports Nutrition for Triathlon Coaches, Bob Seebohar, 2017

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.