Today’s post is written by one of ENC’s Health Professional Advisors, Dr. Jason Karp. Dr. Karp is a nationally recognized running coach, 2011 IDEA Personal Trainer of the Year and owner of RunCoachJason.com. He holds a Ph.D. in exercise physiology. He writes for international running, coaching, and fitness magazines, is the author of five books, including 101 Winning Racing Strategies for Runners and Running for Women, and is a frequent speaker at national fitness and coaching conferences.
The ability to exercise for prolonged periods is strongly influenced by the amount of carbohydrate stored in skeletal muscles (glycogen), with intense endurance exercise decreasing muscle glycogen stores. Most people have enough glycogen to provide energy for only about 70 minutes of running.
At low exercise intensities, some of carbohydrate’s metabolic responsibility for energy regeneration is relieved by fat. Even with the contribution of fat helping to delay the depletion of glycogen, moderate-intensity exercise can only be sustained for two to three hours. With increasing exercise intensity, fat use decreases while carbohydrate use increases. When you run out of carbohydrates, your muscles are forced to rely on fat and consequently your exercise intensity drops because your muscles regenerate energy slower when using fat compared to when using carbohydrates.
Fueling Before Exercise
Many people skip breakfast before doing a workout. Because blood glucose is low first thing in the morning, it’s not a good idea to exercise on an empty stomach, as that would diminish the quality of the workout. At least a half hour before you go out the door to run, eat 200 to 300 calories of carbohydrates and protein, like a bagel with peanut butter. If you run soon after getting out of bed and don’t have at least a half hour before you run, consume 100 to 200 calories, like a nutrition bar, a banana, and a sports drink.
Fueling After Exercise
Refueling nutrient-depleted muscles is possibly the single most important aspect of optimal recovery. And the most important nutrient to replenish is carbohydrate. Muscles are picky when it comes to the time for synthesizing and storing glycogen. Although glycogen continues to be synthesized until storage in muscles is complete, the process is most rapid if you consume carbohydrates within the first 30 to 60 minutes after your workout. Indeed, delaying carbohydrate ingestion for two hours after a workout significantly reduces the rate of glycogen resynthesis. To maximize the synthesis and storage of glycogen, consume 0.6 to 0.7 gram of simple carbohydrate (sugar, preferably glucose) per pound of body weight every two hours for a few hours after your workout.
Protein is another important nutrient to consume after hard and long workouts, especially when trying to build muscle. To repair muscle fibers damaged during training, consume 20 to 30 grams of complete protein (which contain all essential amino acids) after your workout. My research, along with other studies, has shown that chocolate milk, with its high carbohydrate and protein contents, is a great post-workout recovery drink (yum!).