Timing Hydration for Workout Performance

Adequate hydration is an important, yet often overlooked, aspect of exercise.  When a person does not get enough to drink during an exercise bout yet continues to sweat, dehydration occurs.  When sweat loss occurs up to 2% of an individual's body weight, a decrease in performance will be seen.  Some issues that happen as a result of dehydration include the following:

• Increased heart rate - every liter of sweat loss results in an eight beat per minute increase in heart rate.  This means that the heart must work harder to pump blood, which leads to...
• Impaired ability to regulate body temperature - if the heart must work harder to pump blood, the body has a hard time controlling body temperature.  When blood leaves the heart, the skin and working muscles are in competition to receive that blood flow.  Blood must go to the muscles so they have energy to continue exercising, but blood flow must also come to the skin to promote sweating which will get rid of excess heat.  When the heart has to work harder to pump blood, there is a breakdown in this process.  There is not as much blood to go to the muscles or skin, but this doesn't change the fact that the muscles and skin are still in competition to receive blood flow.  If the muscles don't receive adequate blood flow, you don't have energy to continue working out, which leads to early onset fatigue.  This means that you get tired earlier than you would have if you were properly hydrated.  If the skin doesn't receive enough blood flow to dissipate heat, it leads to increased perception of effort - you feel like you are working harder than you really are, which will also lead to early onset fatigue.

What all of this means is that if you are not getting enough to drink during a workout, your performance is hindered.  This is especially important with regard to exercise goals; if you don't have the energy to continue a workout, you will not reach your goals when you want to reach them.  In order to help people understand what they should drink, the Institute of Medicine (2004) put forth guidelines about adequate hydration. These guidelines provide a general idea of what you need; they include the following:

• Children ages 4-8: 5 cups (1.2L) per day
• Children ages 9-13: male - 8 cups (1.8L) per day; female - 7 cups (1.6L) per day
• Adolescents ages 14-18: male - 11 cups (2.6L) per day; female - 8 cups (1.8L) per day
• Adults: male - 13 cups (3L) per day; female - 9 cups (2.2L) per day

If you want a more specific idea of how to hydrate during a workout (i.e. if you are an athlete, or are in training), the following equation will be helpful; don't let the conversions to different measurements in the example equation concern you.  This information may be obtained easily online.

• Preexercise weight - Postexercise weight + amt of fluid ingested during exercise                                                   Hours spent exercising
• This formula = your hourly sweat rate and the number of ounces (mL) you should consume per hour
• Example: A 125lb (58kg) runner practices for 2 hours and drinks a total of 20 ounces (60mL) of fluid during practice.  After practice, he weighs 123 lbs (57kg).
• 125lbs (preexercise weight) - 123lbs (postexercise weight) = 2lbs (1kg) or 32 ounces (960mL)
• 32 ounces (960mL) + 20 ounces (60mL) (this is the fluid consumed during workout) = 52 ounces (1020mL)
• 52 ounces (1020mL)/2 (hours spent exercising) = 26 ounces (510mL) per hour
• This runner's sweat rate is 26 ounces (510mL) per hour.  This individual now knows how many ounces of fluid should be replaced.

The best way to replenish fluid is to drink before, during, and after exercise.  This will keep you hydrated and able to complete your workout.  A few ways that you can accomplish this is to drink non-alcoholic, non-carbonated drinks throughout the day, bring a drink with you when you workout, or leave drinks in strategic spots if you workout in more than one location.  If you know how many calories you lose per hour of exercise, you know how much you need to replace, and can space it out during your workout.

Another thing to consider is intensity; working out at a higher intensity will cause more fluid loss.  In this case, it is a good idea to replenish with a sports drink of some kind.  Be sensible about choosing your sports drink; for instance, if the primary type of exercise you engage in is power walking, you should probably drink a low calorie sports drink rather than a high calorie sports drink.  If you are a long distance runner, you need something with a few more calories in it.  Sports drinks also help replace electrolytes and nutrients that you lose every time you work out, and provide an advantage over water in this way.

An additional consideration is whether you are a "salty sweater" or not.  If you are, this means you are losing more salt than the average exerciser who is not a salty sweater.  If you have ever experienced muscle cramps, sweat stinging your eyes during exercise, or salt on your skin and clothes after working out, then you are probably a salty sweater.  An easy way to fix this is to add 1/4 tsp. for every 20 ounces of sports drink that you consume; and you should definitely be consuming a sports drink rather than water!  A second option is to grab a handful of something salty (i.e. pretzels, peanuts, etc.) directly after finishing your workout.

Proper hydration is essential to having an effective workout.  In order to remain hydrated, you must think through what you need to have on hand before you get to your workout.  Following these tips is a good way to get started on your preparations!

**Information has been adapted from Sport Nutrition for Coaches by Lesli Bonci, MPH, RD, CSSD.