Hydration & Exercise

Have you ever participated in an endurance event or exercised in hot weather? If you have, then you know hydration is key to helping our bodies manage stress associated with increases in body core temperatures. Read on for more information on what’s happening and how to avoid heat related illnesses.

How does exercise change our needs for water?

Depending on humidity levels of the environment, the individual, and sport, mild to moderate work and routine physical training can lead to sweat loss of about 0.8 to 1.4 liters per hour. Exercise raises our body core temperature, and the rate of fluids lost will be increased through sweat to help maintain a normal body temperature. Performance can also be affected if sweat is not compensated. Fluid losses of 2% will impair exercise performance, and losses in excess of 5% can decrease work capacity by 30%.

Why? Because dehydration impairs body temperature regulation and has adverse effects on mental processes, contributing to fatigue. Some common risks for dehydration in sports are inadequate fluid replacement, induced high sweat rates (such as in saunas), laxatives, and diuretics (including substances with a diuretic effect, such as high intakes of caffeinated beverages)

While water is a good option, sports drinks with carbohydrate, sodium, and flavor are better because they contribute to improved performance through increasing water absorption and fluid intake, and are optimal for rehydration.

Why do we need sodium in our beverages?

Sodium is one of several electrolytes found in our body. Electrolytes have a variety of functions including distribution of body fluids, nerve impulse transmission, and muscle contractility. Sodium is critical for exercise recovery and post-exercise rehydration because it helps with replacing sweat loss. A small amount of sodium, (110mg per 8oz), encourages drinking, maintains blood volume, and replaces the sodium lost through sweat.

The extra sodium in sports beverages can also prevent hyponatremia, a condition where sodium levels in blood are lower than normal. Symptoms of hyponatremia include confusion, headache, nausea and vomiting, edema, seizures, and coma. People participating in endurance events, lasting 4 hours or longer, that eat a low-sodium diet, drink a non-sodium beverage, and take NSAIDs, are at increased risk for developing hyponatremia.

Why do we also need carbohydrates in our beverages?

The two main benefits of including carbohydrates in beverages are increased water absorption and fuel for the body. Water may be lost through sweat much faster than it can be absorbed; hence, optimizing water absorption is crucial. While carbohydrates in beverages can assist in fluid delivery and stimulate intestinal water absorption, a very high carbohydrate concentration will instead impair absorption.

Research has shown sports beverages containing 8% carbohydrate had a significantly slower absorption rate than water and other beverages with lower concentration. Also, according to the National Athletic Trainers' Association, using more than one type of sugar (such as glucose and fructose) can optimize fluid absorption.

Thus, beverages with a 6% carbohydrate concentration (or 14g carbohydrate/ 8oz) from more than one form of carbohydrate source can optimize absorption rate. Additionally, both fluid and carbohydrate ingestion can equally improve performance and their effects are additive.

According to a randomized controlled trial published in Medicine & Science in Sports & Exercise, a large volume of either fluid or carbohydrate ingestion improved performance by 6.7% and 6.3% respectively after 50 minutes of intense exercise. However, when fluid and carbohydrates are used in combination, they improved performance by 12.4%.

Carbohydrates can also provide energy for working muscles. Muscle glycogen levels, the essential fuel for exercise, can be depleted after long-term exercise, which means our body cannot provide energy rapidly enough to maintain exercise intensity, resulting in fatigue. Extra carbohydrates in beverages can maintain blood glucose and improve breakdown of carbohydrates to support energy needed for physical activity.

General Recommendation

1. Never let yourself get thirsty! Postponing commonly results in dehydration. Do not wait to start drinking until you feel thirsty, because thirst is stimulated only after a large fluid deficit (1-2% of body mass). The ideal is to drink as much as needed to offset sweat losses. For example, drinking water after each set, or for every 15 minutes of exercise, can help make sure you consume adequate amounts to replace fluid losses.

2. Do not start exercising in a dehydrated state. Because it is difficult to consume and absorb sufficient fluid during exercise, starting exercise in a dehydrated state can only worsen the hydration status. Athletes need to be fully hydrated before training or competing.

3. Choose the right beverage. Sports drinks containing 14g carbohydrates and 110 mg sodium (per 8 oz) will help optimize hydration. Choosing a flavor you like can also increase fluid intake.

Guidelines from ADA, ACSM, and Dietitians of Canada

• Before exercise: drink 12-20 oz, 2-3 hours before

• During exercise: drink 6-12 oz every 15-20 minute

• After exercise: replace 150% of sweat losses (drink 24 oz for every 1 lb weight lost through sweat)

Tips for monitoring and sustaining hydration status

• Have a scale to measure weight lost through sweat

  • Take your weight both before and after workouts

• Have fluid breaks

• Use the urine color chart

For more information, schedule an appointment for a free consultation today!

Content contributed by Yuyi (Amber) Chen currently a bio-major student at Emory University. Originally from Hangzhou, China, Yuyi has been studying in the US for 8 years. Yuyi is interested in nutrition and hopes to use her knowledge to help people maintain a healthy lifestyle.