Keep in mind how your body works in hot weather. The primary way the human body disperses heat is through sweat. Capillaries transport water droplets (and salts) to your skin, where they evaporate, taking heat with them. For athletes, this is tremendously important because of the heat generated during exercise. In fact, about 75 percent of the energy generated during exercise ends up being converted to heat. In maintaining optimal performance, the harder you go, the more you sweat. And when your body begins to run low on fluid for cooling, performance diminishes. Fatigue isn’t the only side effect of dehydration. Serious dehydration can disrupt normal body functions and heat stroke can result.
Fluid intake needs vary by person, of course, but almost all of us are perpetually slightly dehydrated. Sweat levels can vary greatly too, by individual and based on factors like heat, humidity, intensity of exercise, and individual fitness level. In certain conditions, fluid losses can approach a half gallon an hour.
As fluid loss increases, blood volume decreases--this not only strains your heart, lungs and brain, but in athletes it also reduces your body’s ability to deliver oxygen to muscles. Losing 2 percent of your body weight in fluid (common during prolonged activity) can decrease aerobic capacity by nearly 20 percent. This problematic because the more fluid you lose, the less ability you have to sweat.
The sweat that comes to the surface of you skin transports electrolytes with it. That white film that develops on clothes during exercise is comprised primarily of sodium, chloride, potassium, magnesium, and calcium. Each of these components has different properties and contributes to performance in different ways, and each is lost at different rates depending on the individual. While the body stores each of these sweat components, replenishing those stores is crucial for performance. Not only is water insufficient for effective hydration, too much water can have a negative effect--depleting electrolytes at a higher rate.
Effective hydration involves drinking before, during, and after activity. It may seem simple, but in the day or two before exercise or an event, consuming fluids at a slightly higher rate than normal is a good idea. You don’t want to force yourself to drink so much that you gain substantial “water weight” and bloat your stomach though. Avoiding the common state of mild dehydration is the goal. Drinking too much will lead to the inconvenience of more frequent bathroom visits, without providing any performance advantage.
During exercise, the goal is to consume fluids to the point that you lose no more than 2 percent of your body weight. This can take some experimentation (including weighing yourself before and after exercise) in order to find the balance. The American College of Sports Medicine recommends “drinking as much as possible” while not forcing fluids down and causing a sloshy stomach (or gaining weight). It’s important to consume more than just water to avoid depleting electrolyte stores, which can become dangerous (and in rare cases, fatal). The best bet is a drink high in electrolytes, with some carbohydrates. This will help both to hydrate and fuel your workout.
After exercise, it’s recommended you replace 1.2 to 1.5 times the weight lost during the effort. This calculation is relatively easy--a pint of fluid is roughly a pound. You don’t want to rush this consumption because the rapid increase in blood volume will promote urination, which increases the risk of hyponatremia, a dangerous condition more commonly known as water intoxication. Post exercise drinks should include electrolytes, carbohydrates, and protein.
Tips For More Effective Hydration
- Start your day with 8oz of water. It’s an easy amount to consume and can keep you ahead of the game.
- Keep a bottle with you. Having access to water or a sports drink throughout the day can help you avoid that perpetual, mild dehydration. Something with a “sports cap” makes it even more convenient.
- Drink cool drinks. If the beverage is cool on a hot day, you’ll be more apt to consume it. Insulated bottles and cups make it convenient to keep your drink cool.
- Find something you like. If it tastes good, you’re more likely to drink it. Studies have shown that a slightly sweetened drink will result in higher consumption rates.