How much water is enough?
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March 7, 2018
By Mike McKenney, MS, ATC
How much water should athletes ingest during training or competition? That is a common question Athletic Trainers (ATs) are asked on a daily basis. Fluid replacement guidelines intended for the general population are typically insufficient for an athletic population. As a result, care must be taken to deliver advice that is not only evidence-based but realistically implemented. No standardized recommendation or volume of water will be accurate since fluid replacement demands will vary between individuals based on sweat rate, amount of fluid lost during sport and many other physiological variables influencing drinking behavior. This means metrics suggest drinking 1 ounce for every pound or kilogram of body weight are largely inaccurate and depending on activity level, could potentially be harmful.
During exercise, athletes should only drink when they are thirsty and not attempt to ingest as much fluid as they can tolerate.1 The primary reason behind this is safety and an effort to prevent exercise-associated hyponatremia (EAH). Many beverages available to athletes are largely hypotonic in composition, which if ingested in large amounts, can dilute plasma sodium concentrations to dangerously low levels causing EAH or potentially death.1 This includes sports drinks, which are often chosen over water with the intended goal of replacing electrolytes lost through sweat. However, the electrolyte content found in many commercially available sports drinks is inadequate for electrolyte supplementation. The volume an athlete would need to ingest in order to replace their average electrolyte losses would far exceed their fluid losses, resulting in overdrinking and EAH.1,2,3
ATs can play a pivotal role in preventing EAH. In addition to recommending that athletes drink-to-thirst during activity, a red flag for EAH is maintaining or gaining weight during exercise as a result of excessive fluid intake.1 Even though changes in body-weight are not always a reliable measure of overall fluid balance,4 it offers a practical approach for ATs to monitor athletes on a day-to-day basis, especially in situations where fluid ingestion may exceed an athlete’s total fluid losses. Athletes should not fear weight loss during exercise as it is normal and mild to moderate dehydration while drinking-to-thirst does not pose a threat to healthy individuals.1 However, following activity, slightly different strategies need to be employed for fluid replacement.
Thirst is a poor indicator of hydration status in humans. Research5 has demonstrated humans only replace up to 70% of fluid losses if we drink until the cessation of thirst. While this is acceptable behavior during exercise, it can pose problems with maintenance of plasma volume and overall recovery following activity. Athletes should continue to monitor their body weight and continue to drink following activity but in amounts that do not cause them to gain weight beyond what they have lost, as the risk to develop EAH is still present.1 Additionally, athletes should aim to return to their normal weight or prior to their next training session or game. In addition to fluids, replacing sodium post-exercise can also aid in the rehydration process, which will be covered in future blog posts. Please see the below sources for additional material on this topic.
1. Hew-Butler T, et al. Statement of the third international exercise-associated hyponatremia consensus development conference, Carlsbad, California, 2015. Clin J Sport Med. 2015;25(4):303-320.
2. Twerenbold R, Knechtle B, Kakabeeke TH, Eser P, Muller G, von Arx P, Knecht H. Effects of different sodium concentrations in replacement fluids during prolonged exercise in women. Br J Sports Med. 2003;37:300-303
3. Weschler LB. Exercise-associated hyponatremia: a mathematical review. Sports Med. 2005;35:899–922.
4. Tam N, Noakes TD. The quantification of body fluid allostasis during exercise. Sports Med. 2013;43:1289-1299.
5. Nose H, Mack GW, Shi X, Nadel ER. Role of osmolality and plasma volume during rehydration in humans. J Appl Physiol. 1988;65(1):325-331.
The 2017 fluid replacement position statement
Additional Article on Zyrees Oliver
About the Author
Mike McKenney is an Athletic Trainer (AT) at Northeastern University in Boston, Massachusetts, where he is the Medical Coordinator for their Division I men’s ice hockey program. Prior to Northeastern University, he served as an AT in multiple settings including secondary schools, Division I athletics and professional cycling; additionally, he worked as an AT who extends the services of a physician for a large orthopedic group. He has also provided services for many organizations to include the Boston Marathon, USA Cycling and USA Volleyball. McKenney is a hydration and electrolyte replacement consultant for the Atlanta Hawks of the NBA. His professional interests include hydration, electrolyte replacement, thermoregulation in sport and postural restoration. McKenney completed his athletic training education at Gustavus Adolphus College in Saint Peter, Minnesota and master’s degree at North Dakota State University in Fargo, North Dakota. His graduate research was published in the February 2015 edition of the Journal of Athletic Training.