According to James Madison University Exercise Science Professor and Head of JMU Human Performance Laboratory, Michael Saunders, the answer lies in this question: What is the target of your session? Is it to teach the body to use fuel efficiently, which calls for intentionally taking in less fuel, or is it to recover faster in preparation for the next run? If it is the latter, then Saunders considers the duration of your run more than any factor.
"You can find athletes bonking pretty easily, particularly once you get beyond 90 minutes or so," Saunders says. "So really for anything beyond 1 hour and 45 minutes or 2 hours, fueling is a prerequisite for a quality session from which you can recover."
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And for the modern-day athlete trying to manage a busy training, work and family schedule, recovery is the number one priority. Saunders recommends 50 grams of carbohydrate each hour for a session of roughly 2 hours, and for shorter efforts of 60 minutes or less, 20 to 30 grams.
"Even a simple carbohydrate rinse in the mouth for shorter efforts has been shown to improve performance and advance recovery significantly," Saunders says.
"Even a simple carbohydrate rinse in the mouth for shorter efforts has been shown to improve performance and advance recovery significantly."
The Goals of Recovery
Competitive runners from the first Running Boom (circa 1975-1990) often scoff at the notion of fueling for efforts short of a full marathon. It was not uncommon for runners in that era to run for hours with little or no fueling assistance. Today's athletes find themselves recovering from longer training sessions far more quickly with the benefit of proper caloric intake.
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For runs longer than 60 minutes (your long runs and your race), physiologists recommend starting with 30 grams of carbs (roughly 120 calories) every 30 to 40 minutes. Your stomach can absorb up to 60 grams of carbs per hour when diluted with water. By taking in this fuel you will find yourself completing sessions with more energy and recovering from the run more quickly, thereby allowing you to tackle the next day's training.