Hydrating for the Summer Exerciser

The summer has officially taken off, with temperatures climbing into the 100°F, which means it is time to slap on the sun screen, grab the running shoes, and hit the pavement.  As I walked home from work through Central Park yesterday, runner after runner whizzed past me, demonstrating that New Yorkers are out in full force to take advantage of the good weather.  Running is a great exercise, toning muscle, strengthening your heart, and burning calories and I love how much it is a part of the city.  However, with the change in temperatures it is important that those long distance runners equip themselves with the proper fluid and snacks to maximize their work and keep them healthy.

When our internal body temperature rises through exercise and high outside temperatures our body has to disperse the heat, to keep our body temperature in homeostasis.  The body has several methods to accomplish this conduction, convection, radiating and evaporation through sweating; sweating is the fastest and most efficiently way our body can release heat.   We all know we sweat more when it is hot, when we combine this with exercise a person can lose 2-3lbs of water in a 1 hour run.  Some men can lose 4lbs of water in a single workout!  The best way to find out how much fluid you need is to weight yourself without cloths (if possible) before workout and after your workout; the weight change is the amount of fluid you need to drink.  1 liter of water weighs 2 lbs.  This is why drinking water and replacing fluid is so important, with these great water losses it is easy to become dehydrated, which slows down the body and prevents physical gains from the exercise.

Now that we have tackled the water loss during a workout let’s look at a little closer.  Ever tasted your sweat or touched a mirror with a sweaty hand and leave a dirty hand print?  This is from the electrolytes that are lost when you sweat.  The major electrolyte lost is sodium along with a small amount of potassium and chloride.  Drinking water after an intense exercise or lung run will replenish your water loss, but will not help replenish your electrolyte stores.  In fact, if you drink too much water without any electrolytes you can get hyponatremia, low sodium in the blood, which can lead to confusion, convulsions, fatigue, muscle cramps, vomiting, hallucinations, and even coma.

A sports drink, G2 Gatorade, PowerAde, or mixing a GU with 2 cups of water provide you with the proper amount of electrolytes.  If you are going to be exercising for longer than an hour, you will want to drink one of the above mentioned drinks every 20-30minutes to replenish stores, prevent dehydration, and provide your body with energy.

For endurance performance, the optimal drink will supply fluid, fuel, and electrolytes.  Decades of research have demonstrated the benefits of carbohydrates for endurance performance.  The best drinks have 6-7% carbohydrate solutions (14-15 grams/8 ounces).  We need to balance carbohydrate intake with water to slow gastric emptying rate.  We oxidize more carbohydrate when they are provided from a variety of sources (glucose, sucrose, fructose, maltodextrins) rather than from a single source.  Example Gatorade uses sucrose and fructose, PowerAde and GU uses fructose and maltodextrin.

Sport Drink Comparison Table

Sports Drink per 8oz Carbohydrate (%) Carbohydrate (g) Calories Sodium
Gatorade

6

14

50

110

Propel

1

3

10

35

PowerAde

7

17

60

55

GU20

5

13

50

120

You often hear and read about sports drinks adding protein or amino acids, making them super drinks for the avid exerciser.  However while protein is extremely important in recovery, after you have finished a workout, current research shows no benefit of either protein or amino acid during  physical activity other than ultra-endurance events.

What you should look for in a sports drinks:

  1. Electrolytes:
    • Sodium: 100-180mg per 8 ounces (amount in 1 slice of bread)
    • Potassium: 30-70mg per 8 ounces
  2. Carbohydrates: provide every for longer workouts and helps with fluid absorption
    • 14-18g per 8 ounces (50-90 calories)
  3.  The addition of protein, vitamins and herbs are not recommended, there is no evidence of any benefit.


When to use a sports drink:

  1. Duration: Sport Drinks are generally recommended for workouts lasting longer than 1 hour.
  2. Intensity: Higher intensity workouts increase sweating and electrolyte losses.
  3. Environment: High temperatures and exercising in the sun increase fluid losses and the need for a sports drink.
    • Humidity: Above 70% humidity sweat does not evaporate sufficiently to cool the body. Fluid and electrolyte losses increase under these conditions.
  4. Altitude: Exercising at high altitude increases fluid needs.
  5. Sweat Rates: Sweat rates are highly variable, individuals who have higher sweat rates are in a greater need of sport drinks as they lose more fluid and electrolytes.

Post any comments or questions.

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