With marathon and triathlon seasons well underway, both elite and recreational athletes alike are triumphantly completing grueling endurance workouts such as 20-mile marathon training runs, 100-mile bike rides, and long open-water swims.

With such intense training regimens, which often demand back-to-back long-distance workouts, endurance athletes need a sound refueling regimen to optimize each workout and achieve their goals on race day.

During a prolonged, intense workout, an athlete depletes the body’s stored glucose (glycogen). Since the body requires a continual supply of blood glucose for optimal performance, any effort to push through a vigorous workout when glycogen stores are low will lead to sub-optimal performance. Thus, the main purpose of post-exercise fueling is to replenish glycogen stores to help fuel the next long workout.

The average client training at moderate intensities every few days does not need any aggressive post-exercise replenishment. Normal dietary practices following exercise will facilitate recovery within 20-48 hours. But athletes following vigorous training regimens — especially those who will participate in multiple training sessions in a single day (like a triathlete) — benefit from strategic refueling.

Studies show that the best post-endurance workout meals include mostly carbohydrates accompanied with some protein¹. (See the box below for some snack and meal ideas.) Refueling should begin within 30 minutes after exercise and be followed by a high-carbohydrate meal within two hours¹. The carbohydrates replenish the used-up energy that is normally stored as glycogen in muscle and liver. The protein helps to rebuild the muscles that were fatigued with exercise.

The American Dietetic Association and American College of Sports Medicine  recommend a carbohydrate intake of 1.5g/kg (about 0.7g/lb) of body weight in the first 30 minutes after exercise and then every 2 hours for 4 to 6 hours². After that, the athlete can resume his typical, balanced diet. Of course, the amount of refueling necessary depends on the intensity and duration of the training session. A long-duration, low-intensity workout may not require such vigorous replenishment. (This ACE article provides tricks and clues on how to discern if you need a post-workout snack and how to avoid overeating after a workout.)

After an intense workout, it’s also important to restore optimal hydration and electrolyte balance.

If the athlete will have at least 12 hours to recover before the next strenuous workout, then rehydration with the usual meals and snacks and water should be adequate. The sodium in the foods will help retain the fluid and stimulate thirst. If rehydration needs to occur quickly, then an athlete should drink about 1.5L of fluid for each kilogram (or .75L of fluid for each pound) of body weight lost³ (obviously, for this to work, endurance athletes need to weigh themselves both before and after a long workout). This amount of fluid will be enough to restore lost fluid and also compensate for increased urine output that occurs with rapid consumption of large amounts of fluid.

Ultimately, as endurance athletes push themselves physically through their training regimens in an effort to achieve a new personal best or accomplish a new physical feat, they should not underestimate the powerful role of strategic refueling in optimizing athletic performance.

Looking to get into endurance events? Learn about how to train for a half-marathon and how to train for a sprint triathlon.