Macro partitioning
Carbohydrate loading (supercompensation) provides no performance benefit for trained runners during a 20.9-km run, as performance times were statistically identical regardless of initial muscle glycogen levels.
For a 13-mile run, you do not need to perform extreme carbohydrate loading (like eating 500+ grams of carbs for 3 days). Your performance will be the same whether you have 'supercompensated' glycogen or normal levels. Focus on maintaining adequate daily carbohydrate intake rather than trying to maximize stores through extreme diets.
These data demonstrate that (1) muscle glycogen can be elevated to high levels with a moderate exercise-diet regimen; (2) initial muscle glycogen levels influence the amount subsequently utilized during exercise; (3) carbohydrate loading is of no benefit to performance for trained runners during a 20.9-km run.
Why this rating
Randomized crossover design with well-trained subjects, though small sample size (n=6).
Source
Effect of Exercise-Diet Manipulation on Muscle Glycogen and Its Subsequent Utilization During Performance*
W Sherman et al. · International Journal of Sports Medicine · 1981
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