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Is it counterproductive to drink a sports drink or take a gel during a long run if you want to get all the training benefits? – Phil
Apologies to every runner for whom the ritual of loading up with running accessories is half the fun—strapping on the hydration belt or vest, stuffing the pockets with gels and beans and fig newtons. But carb supplementation, via drink or gel or otherwise, short-circuits the purpose of the long run.
You want to drain your carb supply. Here’s why:
On a distance run, you get your energy from an approximately 50-50 split of carbohydrates and fats. The fats are imported from outside your muscle fibers (i.e., cells), but most of the carbs come from the limited supply of glycogen unique to each fiber—think of each fiber as having its own glycogen gas tank.
About 90 minutes into your run, the slow-twitch fibers you’ve been using begin to run out of glycogen. At that point, your body recruits fresh fibers, flush with glycogen, to take their place. In this way, you train previously unused slow-twitch and intermediate fibers that don’t normally get used during distance runs, extending the aerobic benefits of the run to them.
Your nervous system learns how best to recruit these fresh fibers, improving running economy for more intense efforts (e.g., races) that will require them. Your aerobic energy system is forced to burn more fat, a neat trick it will utilize later for less taxing efforts. And the depleted glycogen supply in your muscle fibers triggers a post-run increase in those stores—your gas tank gets bigger. As a terrific 2018 review of studies on glycogen puts it: “Glycogen use during exercise turns on glycogen synthesis [i.e., increased glycogen storage] during recovery.”
On the other hand, ingesting sports drinks and gels during long runs offers muscle fibers an alternative carb source to draw upon, negating the above effects.
Now for the exception: If you include tempo, negative splits, or other fast running in your long run, you’re already using more slow-twitch and intermediate fibers, and you’ll need a steady supply of carbs to maintain your effort without bonking. For these runs, eat or drink up.