Tip of the Month -- July 2006 

Hydration for Performance

How much is just right?

Hydration recommendations can be pretty confusing. In the past, severe cases of heat illness and deaths related to dehydration have caused some organizations to “push” fluids on workers or athletes.  Researchers have shown that thirst is not an accurate indicator of fluid needs since athletes are often already significantly dehydrated (enough to impair performance) by the time thirst kicks in. If thirst is not accurate, how can athletes determine how much fluid they need? The answer is simple. Athletes should strive to replace the fluids they lose as sweat during exercise.

Hydration is critical during exercise, especially during exercise in the heat. The fluids consumed contribute to the athlete’s blood volume, maintaining a constant flow of blood to fuel working muscles and the brain. Additionally, fluids consumed replace the fluid lost as sweat, which is the main avenue for heat loss during exercise. Dehydration of as little as 2% of an athlete’s body weight has been shown to impair endurance performance. For a 150 lb athlete, this would be 3 lbs lost during exercise that should be replaced with fluids.

When athletes don’t drink enough…

When athletes enter a practice or competition in a fluid deficit or does not drink enough during exercise, the fluid loss may cause decreased performance and increased risk for exertional heat illness (such as exertional heat exhaustion and exertional heat stroke). Elevated core body temperature, dizziness, lightheadedness, syncope (fainting) headaches, nausea and weakness are symptoms associated with dehydration and exertional heat illness.

When athletes drink too much…

Drinking too much fluid during exercise is much less common but can have serious health consequences. Exertional hyponatremia is a relatively rare condition where blood sodium levels drop well below normal levels (below 130 mmol/L). Symptoms may include disorientation, altered mental status, headache, vomiting, lethargy and swelling of the extremities (hands and feet) and seizures. This condition usually occurs when activity exceeds 4 hours. Low sodium levels are usually caused by one or both of the following:

1. Ingesting water or low sodium beverages (such as most sports drinks) well beyond sweat losses (known as water intoxication).

2. Sweat sodium losses are not adequately replaced.

The National Athletic Trainers’ Association has established specific recommendations for fluid replacement for athletes, summarized below:

1. Establish a hydration protocol, including a rehydration strategy that considers the athlete’s sweat rate, sport dynamics (rest breaks, fluid access), environmental factors, acclimatization state, exercise duration, exercise intensity

2. Fluid-replacement beverages should be easily accessible in individual containers and flavored to the athlete’s preference.

3. Athletes should begin all exercise sessions well hydrated. The simplest method of hydration status is to compare urine color (from a sample in a clear container) with a urine color chart. Urine color should be pale yellow (like lemonade) not dark yellow (like apple juice).

4. To ensure proper pre-exercise hydration, 500 to 600 mL (17 to 20 fl oz) of fluid should be consumed 2 to 3 hours before exercise and 200 to 300 mL (7 to 10 fl oz) 10 to 20 min before exercise.

5. Fluid should be consumed during exercise to replace fluid lost as sweat.

6. Postexercise hydration should aim to replace any fluid loss accumulated during the practice or event. Ideally, rehydration should occur within 2 hours and should contain fluids (to restore fluids), carbohydrate (to replenish glycogen) and electrolytes (to speed rehydration). When rehydration must be rapid, the athlete should drink “overdrink” 25% to 50% more than sweat losses, to assure optimal hydration 4 to 6 hours after the event.

7. Fluid temperature influences the amount consumed. A cool beverage of 10o to 15o C (50o to 59oF) is recommended.

8. Considerations should be made for very high humidity, which limits evaporative cooling (the air is nearly saturated with water vapor and evaporation is minimized). Sweat is less effect in body cooling and core temperature may increase rapidly due to the inability to dissipate heat. Measuring athletes’ core temperature and environmental conditions are helpful.

9. Consuming carbohydrate during exercise is beneficial if exercise is longer than 45 to 50 minutes or is intense.

10. Coaches and athletic trainers should be able to recognize the basic signs of dehydration: thirst, irritability, and general discomfort, followed by headache, weakness, dizziness, cramps, chills, vomiting, nausea, head or neck heat sensations and decreased performance. Early diagnosis of dehydration decreases the occurrence and severity of heat illness.

11. Inclusion of a small amount of sodium chloride (0.3 to 0.7 g/L) in fluid-replacement beverages should be considered under the following conditions: inadequate salt intake in regular diet, physical activity exceeding 4 hours in duration, or during the initial days of hot weather.

12. Fluid requirements may change during heat acclimatization. (Refer to May’s Tip of the Month for heat-acclimitization recommendations).

13. Implementing a hydration protocol for athletes will only succeed if athletes, coaches, athletic trainers and team physicians realize the importance of maintaining proper hydration status and the steps required to accomplish this goal.

Hydration does not have to be complicated. Drink enough and drink often to perform at your best this summer! 

References

Binkley H.M., J. Beckett, D.J. Casa, D.M. Kliener, P.E. Plummer. National Athletic Trainers’ Association Position Statement: Exertional Heat Illnesses. J Ath Train. 37:329-343, 2002.