Avoiding Dehydration

A case for building a hydration strategy


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Avoiding Dehydration: Abstract

While the physiological effects of dehydration during physical activity are well-researched and somewhat understood by athletes, a convenient, effective method for tracking hydration has been largely inaccessible for most athletes. Keeping properly hydrated during training and/or competition is critical for optimizing performance and maintaining health and safety.

This paper demonstrates the importance of better solutions to combat dehydration and a three-pronged approach to best serve the athlete:

1) appropriate pre-training/competition hydration routine,
2) real-time data during activity enabling optimal hydration at the moment, and
3) proper recommendations for post-exertion rehydration requirements.

Effects of Dehydration on Athletes

The body’s mechanism for maintaining core body temperature is called thermoregulation. Within this process, the body utilizes methods such as convection, radiation, and sweat production for temperature regulation. It is important to note that with sweat production the body introduces fluid imbalances that negatively impact the body both physically and mentally, which in turn impacts the athletic performance of any athlete.

Hydration spectrum by percent body mass change.

Figure 1.
Hydration spectrum by percent body mass change.

Source: Nix generated content

The repercussions of dehydration for athletes do not start and end with decreased performance, there are a variety of physiological ramifications as well, including cardiovascular implications. 

Dehydration imposes a significant endurance performance impairment that drops steeply once the body surpasses 2% dehydration

Figure 3.
Dehydration imposes a significant endurance performance impairment that drops steeply once the body surpasses 2% dehydration

Sources: 4, 5, 6, 7, 8, 9, 10

These negative symptoms of dehydration are unfortunately common, as the current options for tracking and managing sweat losses are not adequate or accessible enough for consumers, or even for high-performance athletes. Popular methods of hydration strategies include drinking ad libitum (drinking to thirst), routine urine testing, or nude weigh-ins before and after activity – each of which has its own challenges.

Implications of Improper Hydration

While many athletes are more informed of the ramifications of dehydration, over-hydrating especially without electrolytes poses many serious results as well. This can occur even when there is a relatively low sweat rate, yet the athlete insists on drinking large amounts of water, or the sweat rate is high and they are replenishing with water only vs. fluids that contain electrolytes. Without the electrolytes the body cannot properly arrive at fluid equilibrium inside the cells compared to outside the cells, thus attributing a greater deficit resulting in conditions such as hyponatremia (low sodium concentration in the bloodstream). In this state, things can quickly escalate from nausea, muscle fatigue, and cramping to a seizure, stroke, or death.

Hydration Tracking for Training Prescription

Thermoregulation is the body’s protective response to rising core body temperature. Even under perfect environmental conditions, as the human body engages in muscular movement the by-product of this activity is heat. As mentioned previously, critical to the process of thermoregulation is sweat production and subsequent sweat evaporation from the skin. While this fluid loss is paramount to keeping the body from overheating, it is imperative for the athlete to be replenishing those fluids appropriately. Teams and individual athletes alike need to have hydration plans in place to curtail the effects of improper hydration and mitigate performance decrements due to dehydration. 

In 2017, almost 60 million people were involved in U.S.-based running, jogging, or walking events (1), including just under 510,000 finishers of U.S.-hosted marathons (2).Many of these individuals are self-coached which increases the need for precise hydration information that is actionable to benefit their overall training, performance, and well-being. Most runners surveyed reported hydration-related incidents during past races; yet, very few used specific hydration plans for their next race (3).

This begs the question: why not? Is it because hydration measurements are complicated and many are not accessible to the average athlete, or is it due to the never-ending guessing game of what sports/electrolyte drink actually works for individual bodies?

The data show the answer is all over the map. Those with higher training volumes leading up to their races were more likely to consume sports drinks during exercise than those with low or moderate training volumes. Most runners heavily relied on the advice of their peer athletes when it came to hydration strategies (3). Of the athletes surveyed 74% indicated that they do not use any method of hydration monitoring despite 45% indicating that they had experienced performance issues due to improper hydration and that hydration was of utmost importance (3).  

What is clear, a hydration-tracking solution will support athletes’ performance and well-being.


Know Sweat

Sweat isn't just water.

Understanding Sweat Composition

Sweat is more than just water, it's also more than just salt. Athletes, especially those not training under the guidance of a coach, need to be considering their electrolyte losses as well. Electrolytes are utilized in the body to conduct electrical signals, these signals do things such as contract muscle fibers, which include both voluntary muscles (like your quadriceps and hamstrings while running) and your involuntary muscles (like your heart which you need for things like basic living).

These are the ones associated with sweating that are good to focus on: 

Sodium - assists with muscle contraction and relaxation, conducts nerve impulses, and assists in water balancing outside of the cell

Potassium - assists in maintaining normal fluid balance inside the cell along with supporting normal blood pressure and contracting muscles

Chloride - works with sodium and potassium to maintain proper fluid balance, but also works with CO2 (carbon dioxide) to maintain the body’s acid-base balance

Until now, athletes have had to resort to trial and error to find products that met their needs for electrolyte replenishment. Asking themselves important questions like “am I a salty sweater yes or no” and going from there. Some athletes have been blessed to quickly find a product that works for them most of the time, while others have to resort to low-key science experiments to solve their hydration challenges. Having a device to conveniently indicate not only hydration levels but also the electrolyte composition of that sweat being lost can drastically alter how an athlete can approach their hydration planning during both training and racing. Through regular data collection, the athlete can begin to know their sweat profile and how their body thermoregulates under a variety of conditions, both environmental and levels of physical exertion. Once an athlete understands their needs in these conditions, even without the real-time data (i.e. if sensor use is not permitted during competition) their hydration prescription is in place and their practiced routine takes over. 

While it has been found that 95% of college athletes and 94% of college coaches agreed that ingesting fluids was important pre, during, and post-exercise, however, only 22% indicated that electrolyte drinks were superior at rehydrating than water for exercise lasting longer than an hour (11).

Hydration status, as mentioned above, is greatly affected by the electrolyte balance associated with this water loss/gain. While many athletes think of gaining their hydration from drinking fluids, roughly 40% of water intake is consumed through food, particularly fresh, non-processed food (12) like fruits and vegetables. This underscores the importance of eating a healthy, well-balanced diet as part of your hydration strategy for all athletes. 

45% of athletes surveyed indicated that they had experienced performance issues due to improper hydration

Building an Athlete Hydration Plan: A Three-Pronged Approach

Access to sweat data is the key to impacting the way athletes think about hydration. This can best be broken down into three prongs of proper hydration: pre-hydration techniques, during workout hydration management, and post/re-fueling.

Pre-hydration techniques: 

Pre-hydration, or drinking fluids prior to your race/activity, is not a new concept. The topic can be found in seminal papers dating to the 1960s and ’70s. Pre-hydration should be thought of as bringing your blood plasma volume to an optimal level before exerting yourself. This allows for a steadier foundation point to begin training from and can assist in better fluid balance throughout the activity, therefore assisting in preventing dehydration by being proactive. It can be further broken down into your general daily hydration habits and your immediate pre-workout hydration methods. 

Adequate water intake for a healthy male between the ages of 19 and 70 is roughly 3.7 Liters/day which is the equivalent of roughly 15 cups of water. A healthy female of the same age range is 2.7 Liters/day or roughly 11 cups (13). Maintaining this level of fluid intake on a daily basis is sufficient to keep your body properly hydrated, in the absence of exercise. Once exercise is added to that day’s activities the body’s hydration requirements increase above baseline daily recommendations. Paying attention to fluid requirements throughout the day, especially in preparation for training and competition, lessens the risk of already being dehydrated before the event begins.

For an athlete’s immediate pre-workout hydration methods, according to Dr. Robert Murray of the Gatorade Sports Science Institute, prehydrating when done appropriately can reduce hydration-related performance issues and health concerns such as hyponatremia. Prehydration should be limited to necessary and reasonable fluid amounts, for example, 20 ounces (2.5 cups) 1-2 hours before exercise, or an additional 8 ounces 15-30 minutes before exercise (14). Having longitudinal data on workouts similar to the one you are about to embark on will allow the athlete to determine what is a reasonable pre-workout fluid consumption amount. 

In addition, this can be facilitated by ingesting a pre-exercise high-sodium fluid beverage prior to exercise and has been shown to increase blood plasma volume, increase exercise capacity, and reduce thermoregulatory strain in hot conditions in both males and females (15, 16).

During workout hydration management

With the previously mentioned hydration tracking methods, real-time tracking was not possible. Popular field hydration monitoring techniques are conducted either before (i.e. urine testing) and/or after (i.e. weigh-ins) – each of which has its own challenges. The most convenient and popular method of managing hydration during exercise is drinking to thirst, however, research shows that this method prompts athletes to only replenish approximately 50% of fluids lost (17).

Training should be preparing the athlete for competition in all aspects of their functioning. It has been found that runners, in general, have a heightened sense of awareness of the performance impacts of proper nutrition, which includes hydration tactics, yet the diligence with which they prepare on actual race day is not the same diligence they may put into their typical training days (3). This is a missed opportunity for many athletes if an athlete trains in an optimal state their baseline level of performance increases. If they train at a deficit it could lower the athlete’s performance ceiling during competition. 


Athletes have been found to not adequately determine their fluid losses during activity, particularly if the athlete is rehydrating based on thirst (18). Once this occurs, post-workout rehydration is critical, having an indication of how large the gap is between losses and requirements allows the athlete to have context in what they should focus on rather than it being guesswork. Even with a tool indicating in-real-time notifications, the athlete could feel more comfortable waiting until after activity to complete the entirety of their rehydration requirements; particularly if it is either a shorter bout of exercise or they are refueling with a glucose-based product.


Access to hydration and rehydration information, aka a hydration check, is critical for athlete performance, particularly if the athlete is not under the supervision of a coach. This knowledge allows the athlete to formulate and modify their hydration prescription based on the intensity of the training session or competition, as well as under what environmental conditions they are competing. More importantly than performance, this information will help mitigate hydration-related injuries and incidents. 


(1) https://www.statista.com/topics/1743/running-and-jogging/

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(14) Kundrat, S. (2003). Sports nutrition: current research on hydration, postexercise refueling and the glycemic index. IDEA Health & Fitness Source, 21(10), 50-55.

(15) Sims ST, van Vliet L, Cotter JD, Rehrer NJ. Sodium loading aids fluid balance and reduces physiological strain of trained men exercising in the heat. Med Sci Sports Exerc. 2007 Jan;39(1):123-30.

(16) Sims ST, Rehrer NJ, Bell ML, Cotter JD. Preexercise sodium loading aids fluid balance and endurance for women exercising in the heat. J Appl Physiol (1985). 2007 Aug;103(2):534-41.

(17) Kenefick, R. (2018). Drinking Strategies: Planned Drinking Versus Drinking to Thirst. Sports Medicine, 48, 31-37

(18) Love, T. D., Baker, D. F., Healey, P., & Black, K. E. (2018). Measured and perceived indices of fluid balance in professional athletes. The use and impact of hydration assessment strategies. European Journal of Sport Science, 18(3), 349-356.