by Julie Hansen, M.S., R.D., C.D.

Proper fluid replacement before, during, and after exercise can positively influence how you feel and how you perform.  Most people do not realize how quickly water can be lost from our bodies when exercising.  The heat production rate in active, exercising muscles can be 100 times that of resting muscles.

On the average, the body loses more than two liters of water each day through perspiration, urine, feces and respiration.  During exercise, sweat losses of up to three liters/hour are common.  Technically, dehydration occurs when body water loss equals one percent of body mass (performance is affected at a fluid loss of two percent).  For example, a 150 pound person becomes dehydrated after losing one and one-half to three pounds of body weight.

Thirst is an unreliable indicator of fluid needs after exercising in hot weather, partly because the intake of water quickly dulls the thirst sensation.  Further, rehydration with plain water dilutes the blood rapidly and stimulates an increase in urine production that leads to greater dehydration.

Rehydration will occur more rapidly when beverages containing sodium (the major electrolyte lost in sweat), are consumed.  Ingesting a beverage containing sodium allows the plasma sodium to remain elevated during the rehydration period and helps maintain thirst while delaying stimulation of urine production.  The rehydration beverage should also contain glucose or sucrose because these carbohydrates provide a source of energy for working muscles, stimulate fluid absorption in the gut, and improve beverage taste.

The following guidelines will help athletes maintain proper hydration during practice and competition:

• Weigh in without clothes before and after exercise, especially during hot     weather.  For each pound of body weight lost during exercise, drink 2   cups of fluid.
• Consume a sports drink containing sodium to quickly replenish lost body fluids.  The beverage should contain 5-8% glucose or sucrose.
• Drink 2.5 cups of fluid two hours before practice or competition.
• Drink 1.5 cups of fluid 15 minutes before the event.
• Drink at least 1 cup of fluid every 15-20 minutes during training and competition.
• Limit beverages containing caffeine and alcohol because they increase urine production and add to dehydration.

5% Carbohydrate:

4 Tbs. sugar

4 cups water

1/8 tsp. salt

2 Tbls. lemon juice

6.5% Carbohydrate:

5 Tbs. sugar

4 cups water

1/8 tsp. salt

2 Tbls. lemon juice

Julie Hansen, M.S., R.D., C.D. is a Registered Dietitian and Exercise Physiologist.  She has been running competitively in road races since 1980 and competing in triathlons since 2005.  Julie currently teaches a Sports Nutrition course for Weber State University and a Weight Management course for the University of Utah.  She is the dietitian for the Weber State Athletic department and works part time as a dietitian for Kimberly Clark Corporation in Ogden, Utah and for Solstice Residential Treatment Center in Layton, Utah.  Julie also has a private nutrition practice in Utah working with individuals who want to lose weight, improve performance, lower cholesterol or prevent disease.