Drinking water during exercise is important, but it is not always enough to maintain performance. During long training sessions, endurance events, and exercise in hot conditions, the body loses not only water through sweat, but also electrolytes, while energy demands continue to increase.
That is why even athletes who drink fluids regularly can experience a decline in performance. The question is not only how much fluid is being consumed, but also what is being lost and what needs to be replaced.
What happens when sweat loss increases?
During exercise, especially in hot environments, sweat production increases to help the body dissipate heat. When fluid losses exceed fluid intake, total body water and plasma volume decrease.
This can increase heart rate, make thermoregulation more difficult, and increase perceived exertion. Research suggests that greater levels of dehydration may be associated with increased perceived effort during endurance exercise.
Therefore, during longer or more intense sessions, simply drinking water may not be enough to meet all of the body’s demands.
Water isn’t the only thing lost through sweat
Sweat is primarily composed of water, but it also contains electrolytes, particularly sodium. Sweat sodium concentration varies considerably between individuals, meaning that two athletes completing the same workout may have very different losses.
This becomes especially relevant during prolonged exercise, high sweat rates, or exercise performed in the heat.
Consuming fluids containing sodium can help support fluid retention and maintain fluid and electrolyte balance. In addition, beverages containing carbohydrates and electrolytes may be useful when a strategy needs to address both hydration and fuel requirements.
Hydration also needs to consider exercise duration
During a short workout, water may be enough to meet fluid needs. As exercise duration increases, however, other demands become increasingly important.
During prolonged exercise, carbohydrate intake helps provide energy to maintain intensity. Combining carbohydrates, fluids, and electrolytes may therefore be more appropriate than considering hydration on its own.
This is particularly important during endurance events, when athletes need to sustain effort for several hours.
What about exercising in the heat?
Heat makes an individualized hydration strategy even more important.
Higher temperatures increase the body’s need to dissipate heat and can increase sweat rate. When these losses are not adequately managed, the resulting effects on the cardiovascular system and thermoregulation can contribute to a decline in performance.
In addition, the combination of heat and dehydration can increase carbohydrate utilization during exercise, further emphasizing the importance of an appropriate nutrition strategy during prolonged events.
How can you tell if hydration is adequate?
There is no universal amount of water that works for every athlete. Fluid requirements depend on factors such as exercise duration and intensity, temperature, humidity, body size, and, most importantly, sweat rate.
One practical way to individualize a hydration strategy is to estimate sweat losses during training.
Athletes can compare their body weight before and after exercise, while also considering the amount of fluid consumed and urine losses during the session. This provides an approximate estimate of fluid loss and can help adjust intake during future workouts.
More important than trying to completely prevent any reduction in body weight during exercise is avoiding excessive losses and developing a strategy that is comfortable and sustainable for the individual athlete.
Hydrating doesn’t mean drinking as much as possible
If drinking too little can contribute to dehydration, drinking too much can also be problematic.
Excessive fluid intake, particularly without adequate sodium replacement, can contribute to a decrease in blood sodium concentration, known as exercise-associated hyponatremia.
Therefore, the strategy should not simply be “the more water, the better.” The goal is to find a balance between individual losses, fluid intake, and electrolyte replacement.
In practice: hydration is part of a bigger strategy
For endurance training and racing, thinking about hydration in isolation can leave out an important part of the overall strategy.
It is necessary to consider:
- Sweat rate: how much fluid the athlete actually loses.
- Exercise duration: the longer the session, the greater the need to plan fluid and fuel intake.
- Temperature and environmental conditions: heat and humidity can significantly increase sweat losses.
- Sodium: particularly relevant when sweat losses are high or exercise is prolonged.
- Carbohydrates: important for maintaining energy availability during longer and higher-intensity exercise.
- Gastrointestinal tolerance: the strategy should be tested during training, not for the first time on race day.
Maintaining performance therefore depends on more than simply starting exercise well hydrated or carrying a bottle of water. It requires understanding the demands of the effort and developing a strategy that accounts for fluid, electrolyte, and energy losses throughout exercise.
Conclusion
Hydration is essential for performance, but hydrating does not simply mean drinking water.
During prolonged exercise, particularly in hot conditions and when sweat rates are high, fluid losses occur alongside electrolyte losses, while energy requirements continue throughout the effort.
An effective strategy should therefore consider the athlete as a whole: how much they sweat, how long they will exercise, the environmental conditions, and their carbohydrate and electrolyte requirements.
