Thursday, March 12, 2015

Fluid Replacement Beverages for Athletes: Why rehydration is so crucial and how to do it most efficiently

Fluid replacement beverages can be used in a wide variety of circumstances, but are most commonly associated with their use by athletes to optimize physical performance. Studies have shown that even modest dehydration (2 percent of body weight) can result in as much as a 20 percent decrease in physical performance in normal temperatures, and up to a 40 percent decrease in physical performance in hot temperatures. It is clear that remaining well hydrated is crucial to performance, but simply drinking water may not be the most efficient solution. Progressing knowledge of human physiology has revealed that specific concentrations of additives to water can actually help to improve performance. Most of us are aware of the popular branded fluid replacement beverages such as Gatorade, Powerade, Muscle Milk, etc, but recent studies have revealed that fluid replacement beverages should not be treated equally among athletes. Different compositions are beneficial for different purposes. For example, endurance athletes would benefit from specific concentrations of components, such as water, sodium and carbohydrates, in their drinks that differ from those that would be most beneficial to athletes performing a lot of work in a short amount of time.

Sodium and its anions comprise the most active components of the extracellular fluid, while potassium and magnesium are the most abundant cations in the intracellular fluid. The imbalance of sodium and potassium across the compartments is critical to cell function and electrical activity throughout the body. The gradient of these electrolytes is maintained by the sodium-potassium pump. When we exert physical energy for a sustained period, or in strong bursts, we lose sodium and several other electrolytes in our sweat, including chloride, potassium, and magnesium. The replacement of these electrolytes is essential for maximum physical exertion to be reached. Studies have shown, however, that athletes drinking both during and after exercise usually do not fully replace the fluids lost through sweat, and it is important to note that the consumption of too much water risks diluting the existing levels of electrolytes in the body, causing further difficulty in electrical signaling (termed hypohydration). Hypohydration is common in athletes and can cause serious consequences in terms of cardiovascular and thermoregulatory function which can seriously affect performance (in both prolonged aerobic exercise and sports involving intermittent repeated high intensity actions). Hypohydration (as little as 1 to 2 percent) has also been shown to have significant effects on energy metabolism, causing increased lactate, among other pain and fatigue causing occurrences.

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The main objective of fluid replacement beverages is to avoid the complications caused by hypohydration by simply replacing the fluid lost, but as this brief summary exemplifies, there are other factors that can be positively influenced by fluid replacement beverages that are associated not only with rehydration, but with performance enhancement. Performance enhancing components can contain carbohydrates for energy, caffeine for stimulation of the central nervous system, and proteins to promote muscle recovery. Studies have shown that athletes generally consume replace than 50 percent of the losses from sweat during both practice and competition. The ideal hydration practice would be to replace fluids, and their components such as sodium and other electrolytes, at the same rate as they are being lost. The losses from sweat are very difficult to estimate, which makes the formulation of sports drinks challenging to contain the proper balance of components for the individuals consuming them (due to the huge range in exertion and external environments of individuals). 

Despite the observed challenges, some studies have shown general trends in efficacy of some tactics for optimizing performance during physical exertion. Before exercise, there have been positive benefits exemplified in athletes who “sodium load” before exercise to put the body in a state of hyperhydration which has been shown to delay the amount of time it takes for bodies to reach a state of hypohydration where serious physical constraints start to be felt. In addition, the consumption of caffeine before exercise (particularly in endurance performers) has been shown to improve endurance and in some cases has also been shown to improve performance in stimulated team sports. Be aware that the positive effects of caffeine only require a small amount to be beneficial and that too much caffeine consumption can have negative side effects (think 5-6mg/kg).

During exercise, the consumption of sodium is universally crucial. Sodium will stimulate the consumption of more fluids to better replace losses, and its ingestion with potassium and chloride, together, will replace much of the lost sweat electrolytes. Sodium has also been shown to be effective in mitigating or preventing cramping during exercise, which can be crucial to performance. Finally, the inclusion of carbohydrates in fluid replacement drinks during exercise has been shown to be effective in delaying muscle fatigue and improving overall performance in both endurance and high intensity short duration activities, though overconsumption can be detrimental to performance.

After exercise, the most important components in fluid replacement are: proteins, sodium,  and carbohydrates to stimulate better rehydration, muscle recovery, and improve fluid retention. Interestingly, some studies have shown that milk is often more effective at providing these benefits than electrolyte infused sports drinks due to its natural chemical properties, possibly due to the casein in milk.

When exercising, consider the specific physiological benefits of the fluid replacement beverages you choose to drink based on your specific environmental, physiological, and individual characteristics to benefit as much as possible in both performance and recovery.

Baker, L. B., & Jeukendrup, A. E. (2014). Optimal Composition of Fluid‐Replacement Beverages. Comprehensive Physiology.


  1. This is very interesting. I never even considered hypohydration. I guess this means that grabbing a powerade every time I head to the gym won't be such a bad idea. The point you made about caffeine was very interesting to me because I had heard it before. But your recommended dosage of 5-6 mg/kg seems like a lot! I weigh about 62 kg (and I'm fairly thin), which would amount to about 310-372 mg of caffeine. The average cup (8 fl. oz.) of coffee has about 95 mg of caffeine. So when you say just a little bit of caffeine is required I was expecting one cup, not 4 cups! Are you sure about the dosage?

  2. As an athlete I thought about this in a practical way, such as how would I replenish fluids during exercise in order to maintain the proper sodium concentration. It would make sense that replenishing things that you lose would make you not cramp, increase muscular endurance, etc. But I have found in practice oftentimes that those who do attempt to completely replace all of the fluids and sodium that they lose are those who end up with stomach cramps because of the amount of liquid there. I just think it is interesting to consider how the ideas of rehydration work out in theory and in practice (literally).

  3. Similar to Sarah, I am also a student-athlete, and hydration is a key concern of mine throughout the day. For a while, I only thought about keeping hydrated while I was at practice or at a track meet, but my coaches also reminded me to drink water throughout the day. I now carry my water bottle with me everywhere, typically have a bottle of Gatorade at some point in the day, and always enjoy a cup or two or chocolate milk after a workout! Now I can certainly see why it is important to consistently replace your fluids as it is lost, and understand how beneficial it can be for performance purposes in a more concrete way. After reading this, I can also see how too much hydration in too short period of a time can be detrimental to athletes, and I think it’s definitely something that many of us do not consider from day to day.