If your a runner you must read this.

When you run, you sweat. The more you sweat, the more your blood volume decreases. The more your blood volume decreases, the harder your heart has to work to deliver oxygen to your working muscles.

Although it doesn’t supply calories, vitamins, or minerals, water is essential for virtually every bodily function. It aids digestion, cushions organs, and keeps your body temperature from rising to lethal levels during exercise. In fact, H₂O is so important that it accounts for 55 to 65 percent of your weight.

Just like cramming for a test, binge (water) drinking the morning of a long run won’t hydrate you properly. Aim to drink about 2-3 mL per pound of body weight at least 4 hours before your run. If you chug an entire litre of pre run water, the kidneys will flush it out, causing frequent mid run bathroom breaks. You may even dilute the body’s sodium balance and increase your risk of developing hypernatremia (or water overload) during your run. Instead, keep a water bottle handy all week and drink throughout the day. Your urine colour should be light yellow (like lemonade). Once it gets too dark (like apple juice), you’re already dehydrated. 

Another good way to determine hydration status is a sweat test, says Chrissy Carroll, R.D., USAT Level I Triathlon Coach. “Weigh yourself, without clothing, before and after a long run. If you've only lost 1 to 2 Percent of your body weight, you’re in the hydration sweet spot. If you've lost more than 2 to 3 Percent of your body weight, try hydrating a little more during your long runs.” 

There is no standard fluid recommendation for runners because every runner has a different sweat rate, speed, body size, and training efforts. A good starting point is to drink 0.4 to 0.8 litres of water in the first hour. For a run lasting longer than an hour, consume 0.5 to 1 litres of sports drink to replace lost fluid, salt, and carbs. If you lose more than 2 to 3 Percent of body weight during your run, drink 1.5 litres of fluid for each kilogram of body weight lost. 

Your Fuel Consists of Gels and Chews But No Sports Drinks

“Many athletes prefer the convenience of gels for fuel,” says Carroll.  Gels and chews have plenty of sugar to avoid mid run bonk, but they don’t always have enough sodium to maintain fluid balance. “Add an electrolyte mix to your water or incorporate a salt tablet during long runs or races.” But be sure to try this in training to make sure it works for you on race day. 

You Don’t Get Enough Magnesium or Potassium

Most runners know about sodium, but sweat also contains magnesium and potassium, which play a pivotal role in maintaining fluid balance and muscle function. Most Americans don’t consume the recommended 400 mg of magnesium and 4,700 mg of potassium each day. A deficiency in either mineral can exacerbate the symptoms of dehydration and cause extreme muscle cramps. 

A well-balanced diet, rich in fruits, vegetables, grains, and legumes will ensure you get enough of these nutrients. These sources are particularly good choices. 

Magnesium: Leafy greens, almonds, pumpkin seeds, tofu, flaxseeds, broccoli, lentils
Potassium: Bananas, sweet potatoes, beets, tomatoes, oranges, pomegranate juice

Dehydration, says Dr. Coyle, may cause increased metabolic stress on muscles and faster glycogen depletion. It also wreaks havoc on your internal thermostat by decreasing blood flow to the skin, slowing your sweat rate, and increasing the time needed for fluids to be absorbed into the blood stream. What’s worse, by the time you feel thirsty, your body has already lost up to two Percent of its weight

Signs of Dehydration.

Do you urinate less than three times during a normal day? Is your urine dark yellow? Does it have a strong odour? Do you get headaches toward the end of a long ride or shortly afterward? Do you drink less than 500ml per hour while running? Do you lose more than two pounds during runs? If you answer yes to any of these questions, your body is heading for a drought. Time to start drinking more until the situation is rectified.

water, sports drink or flat coke?

What you drink makes a difference. In a study conducted by Dr. Coyle, dehydrated athletes were asked to drink nearly two litres of fluid two hours after they exercised. The catch is that these athletes drank diet cola, water, or a sports drink. The study then compared the quality of replenishment each provides. Dr. Coyle found that

cola replenished 54 Percent of the fluid loss;

water, 64 Percent;

and sports drink, 69 Percent.

Snack on Something a Little Salty

Sodium makes your blood sponge-like, allowing you to absorb more water and excrete less. Each litre of sweat saps between 500 and 1,000 (or more) milligrams of sodium.

Choose Juicy Foods

Around 60 Percent of your daily fluid comes from the foods you eat, but some foods increase hydration better than others. For instance, fruits and vegetables are great fluid sources; they are 80 to 95 Percent water by weight. Eating the recommended five to nine daily servings of produce means that you will get a lot of extra water in your diet. If you are downing protein supplements, you should drink even more water, as you will need that additional water to metabolize and excrete the extra protein.

Sports Drinks Can Be Your Friend

Most popular sports hydration drinks contain sodium, potassium, and other electrolytes as well as energy-producing carbohydrate. These drinks are recommended for exercise that lasts more than an hour. Whenever you plan a long run, make sure you carry enough fluid. In addition, have a plan to fill up along the way. Whichever brand of sports drink you choose, make sure you like the way it tastes so that you’ll be motivated to drink. Also, cool fluids taste better and may be absorbed more rapidly than warm ones.

Give Beetroot a Try

Sure, we may someday find out this was just a fad, but there is growing evidence that nitrates such as those found in beet juice can help boost aerobic performance, says Matt Pahnke, PhD. It’s shown some benefits as far as improving efficiency, meaning that the same amount of work requires less oxygen. And that is obviously a good thing.

You do not necessarily need a sports drink on every run.

Since you do not seek to test your performance limits in most of your runs, it is not necessary to use a sports drink every time you lace up your shoes. Go ahead and use plain water in your easier runs and save the sports drink for your faster and longer workouts. I would advice isotonic drinks on runs or any workouts lasting over 50 minutes to an hour.

Maintaining access to fluids during runs can be challenging. You can carry some fluid in a squeeze bottle stashed in a fluid belt worn around your waist, but you cannot carry enough fluid in this manner to cover your longest runs. To ensure that you have enough fluid to cover these runs, either plan to return home midway through the run to refill your bottle or carry some money and refill your bottle at a convenience store. A friend of mine who lectures on personal training and all things sports related stashes water and food at strategic points around a run or bike ride (he is a triathlon) so he has certain points on his training route to replenish those lost nutrients.