Staying hydrated during exercise

Drinking fluids during exercise is essential for you to remain hydrated and maintain your physical and mental performance. When you become dehydrated, the overall amount of water in your body declines to the extent that you can lose more than 2% body weight. This fluid loss negatively impacts your cardiovascular system, body temperature, and muscle function. To avoid dehydration, consume fluids during exercise in small amounts (3–8 fl oz) every 15 to 20 minutes. One gulp is about 1–2 fl oz.

What to drink

Water is fine if the exercise is moderate and of short duration, but if the exercise is intense or longer than one hour, the fluid you drink should contain carbohydrates and electrolytes, such as in a sports drink. Water and electrolytes (sodium, potassium, chloride, and others) serve very important roles in the functioning of your body, and sweating during exercise can lead to excessive losses of both critical nutrients if not properly replaced. If sweat water and electrolyte losses are not replaced, physical and mental performance can be severely compromised. Dehydration and electrolyte deficits can cause symptoms such as dizziness, confusion, rapid heartbeat, and muscle cramps.

The addition of carbohydrates in a sports drink can enhance the absorption of water and help maintain blood sugar levels during exercise, which might preserve muscle glycogen (sugar storage) and thereby delaying fatigue. For more information, see HPRC’s article on sports drinks.

Important tips for hydrating during exercise

  • Don’t rely on thirst as a good indicator of your fluid needs. If you’re thirsty, it’s likely you’re dehydrated. Consuming fluids at regular intervals throughout the day will prevent dehydration. But always begin exercising well hydrated. To ensure this, drink 14–22 fl oz of fluids about 2 to 4 hours before strenuous exercise.
  • Sustained exercise, especially in the heat, can result in high sweat rates and substantial water and electrolyte loss. As discussed above, a sports drink with carbohydrates and electrolytes is important to replace lost nutrients.
  • Conversely, too much fluid can result in hyponatremia (low salt levels in the blood), which is life threatening. During exercise, limit your fluid intake to one quart per hour, or up to 1.5 quarts per hour in hot weather, to avoid hyponatremia. Do not drink more than 12 quarts per day. Women can be at greater risk than men of developing exercise-associated hyponatremia.

The bottom line

The amount of fluid and sweat you lose depends on the intensity of your exercise, environmental conditions, and the type of clothing you wear during the exercise. If you’re exercising under heat and physical stress, pay special attention to fluid, carbohydrate, and electrolyte intake. Maintaining hydration status is especially important for the Warfighter because it affects performance. To learn more about hydration and the military, visit HPRC’s Warfighter Nutrition Guide.

References

Institute of Medicine, Food and Nutrition Board, Panel on Dietary Reference Intakes for Electrolytes and Water, & Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (Eds.). (2004). Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC: The National Academies Press.

Academy of Nutrition and Dietetics, Dietitians of Canada, & American College of Sports Medicine. (2016). Nutrition and athletic performance. Medicine & Science in Sports & Exercise, 48(3), 543–568. doi:10.1249/MSS.0000000000000852.

Rosenbloom, C.A., & Coleman, E.J. (Eds.). (2012). Sports Nutrition: A Practice Manual for Professionals (5th ed.). Chicago, IL: Academy of Nutrition & Dietetics.

Sawka, M.N., Burke, L.M., Eichner, E.R., Maughan, R.J., Montain, S.J., & Stachenfeld, N.S. (2007). Exercise and fluid replacement (American College of Sports Medicine position stand). Medicine & Science in Sports & Exercise, 39(2), 377–390. doi:10.1249/mss.0b013e31802ca597.

Headquarters, Departments of the Army, the Navy, & the Air Force. (2017). Nutrition and menu standards for human performance optimization (AR 40–25/OPNAVINST 10110.1/MCO 10110.49/AFI 44–141). Departments of the Army, the Navy, and the Air Force, Washington, DC, Retrieved from: https://armypubs.army.mil/epubs/DR_pubs/DR_a/pdf/web/AR40-25_WEB_Final.pdf.