Most runners have repeatedly heard that advice that the must drink fluids as the summer months approach or when heat waves strike. Well duh, who doesn’t drink when it’s hot?
Instead of boring you with yet another “news flash” article about how you need to drink more when it’s hot, I’m going delve into some of the specifics of summer hydration – when you should be drinking water versus when you should be drinking sports drinks (or an electrolyte beverage) and how to calculate exactly how much fluid you need on any given training run.
To preface, this article is about hydration and drinking protocols during training, not during a marathon race or while you’re practicing your marathon nutrition strategy. During marathons or fueling for marathon specific long runs, refueling is important and another topic entirely.
Fluid Absorption Rate
First, it’s important you understand how sugar and electrolytes impact your fluid absorption rates. The speed at which water, electrolytes, and sugars can be absorbed into the blood stream is one of the main determinants of what type of beverage you should choose when trying to stay hydrated.
The absorption of fluids into the body is largely dependent upon two factors: (1) the rate at which it is absorbed through the walls of the small intestine; and (2) the speed at which it is emptied from the stomach. Both of these factors are controlled by the composition of a liquid in terms of its carbohydrate (sugar), and electrolyte concentrations.
As a general rule, the higher the carbohydrate content of your beverage, the slower the absorption rate will be. Consequently, trying to maintain proper hydration and balanced electrolyte levels during a run with sugary sports drinks is difficult. On the other hand, plain water passes through the body too quickly and without providing the necessary sugar to spark the insulin response and ignite the recovery process.
Therefore, your choice for hydration will depend on whether your primary aim is rehydration (keeping the body cool and maintaining fluid balance) or the replenishment of energy (sugar and electrolyte stores).