Eve Wulf
Friday July 22nd, 2016

Water is the lifeblood of all living things, but the compound is especially the lifeblood of all athletes, as most studies have shown that when the body loses greater than 2% of its body mass, performance is affected. How much do you actually know about the effects that dehydration can have on performance? What can you do to prevent and identify dehydration before, during and after your next performance?

Dehydration, debunked

According to Brett Ely, a senior doctoral student at the University of Oregon and a former researcher for the United States Army Research Institute of Environmental Medicine (USARIEM), the main reason athletes become dehydrated is due to the sweat loss during exercise. As soon as an athlete’s body temperature begins to rise, the body will begin to produce sweat, which leads to an aggregate loss in water from the body. Athletes also lose water through respiration during exercise. When the body begins to lose that much water, the excreted water comes in part from the body’s plasma volume, which decreases total circulating blood volume. With a lower plasma volume, the blood’s viscosity increases and the heart’s stroke volume decreases, causing the heart to work harder. 

Dehydration and performance

As the body becomes increasingly dehydrated, the ability for an athlete to perform at the highest level is affected.  The effect of dehydration on performance is predominantly seen in aerobic events. As Ely confirmed, dehydration largely takes a toll on aerobic performance, such as running, cycling, swimming, or soccer. Since these sports require high levels of endurance and sometimes do not allow for the athlete to rehydrate habitually, the body demands far more water for blood flow, which increases the risk for severe dehydration. Accordingly, aerobic performance is affected because when the athlete’s heart is required to pump a decreased blood volume to all muscles and organs that demand it, the athlete fatigues more easily and is not able to sustain the same endurance throughout.

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In addition to aerobic performance, the effects of dehydration on performance are especially seen in hot temperatures. In a study that Ely participated in while at USARIEM, she noted that in the coldest temperatures, a body that was dehydrated by 4% did not experience a large impact in performance. However, as ambient temperature rises, dehydration begins to have a greater impact on performance. “The reason for this is that your body needs to get the blood to your active muscles during exercise and if it’s hot, the body also needs to get that blood flow to your skin to cool you. If you’re trying to cool yourself while also maintaining blood flow to the muscles, and you also have less blood volume because of dehydration, the impact on performance will be magnified in a hotter environment.”

If you are exercising in the heat and losing large amounts of water through sweating, staying hydrated becomes particularly important, not only because it helps you perform better because of the larger detriment of dehydration in the heat, but it also helps to reduce your risk of developing a heat injury, Ely notes.

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Ely also mentions that dehydration could potentially cause performance impairments through changes in mood. In a recent experiment that Ely conducted on dehydration and cognitive performance, she noted that an athlete’s mood can change with the onset of dehydration, and that if an athlete does not feel well, performance could be impaired due to decreased motivation and potentially compromised decision-making abilities.

Preventing and identifying dehydration


The best way to prevent dehydration from allowing you to perform at your best is understanding how to avoid and identify dehydration. According to Ely, the simplest way to gauge your hydration level is to check the color of your urine. If it’s pale yellow, you are likely well hydrated. If not, drink more water, but don’t chug, as that could cause your body to excrete the water too quickly. Prior to a performance, Ely recommends sipping water in the days leading up to the event, as well as maintaining a healthy diet. “Any fruits or vegetables will give you additional fluids, and then foods that have higher sodium and potassium will take the place of electrolytes to maintain balance. Eat a normal amount of salt; don’t avoid it or overdo it.”


In terms of mid-performance, thirst and dry mouth is the telltale sign of dehydration. Thirst is perhaps the easiest way to assess hydration, and Ely suggests using thirst as a guide to prevent severe dehydration or over hydration during exercise. To combat dehydration, Ely suggests training with fluids during exercise to prepare your gut to absorb fluid while exercising so that you can take in and absorb water at an ideal rate. “Maintaining your fluid balance throughout exercise is ideal.”

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In regards to muscle cramps, Ely mentions that the link between muscle cramps and dehydration is not well established, as muscle cramps can be caused by many things. Similarly, the signs of dehydration and heat exhaustion are very similar, so Ely notes that it becomes easy to misidentify dehydration. “The times you’re most likely to dehydrate is when you’re exercising in the heat and if you get overheated, the signs are similar to dehydration. You might have nausea and light-headedness, so it becomes difficult to distinguish between the two.”

But don’t completely disregard light-headedness, which is a symptom of postural hypotension and occurs when you go from sitting to standing quickly. “That could be a sign your body fluids are low,” Ely states.


Knowing your hydration level after a performance is also important. Ely has suggested that the best way to monitor your hydration is by using your urine, body mass and thirst level as an indication of how dehydrated you may be. If your urine is dark yellow or you are experiencing infrequent urination, you’re likely dehydrated. Similarly, if you have lost body mass while exercising, your body’s fluids need to be replenished. “If you’ve lost three pounds in a one hour exercise, you need to drink at least three 16oz glasses of fluid to make up for that. It helps to keep you on top of hydration over time.”

Post-performance hydration

Post-performance hydration is just as important as pre and mid-performance hydration. In terms of the normal body water loss that occurs over the course of regular exercise, Ely advises re-hydrating with water or a sports drink with electrolytes. However, if you’re not going to eat soon after exercising, an electrolyte drink is best for helping to maintain the electrolyte balance in your blood. Without food, plain water could dilute the remaining electrolytes. But, if you are eating, the sports drink becomes less important since the sodium and potassium from food replenishes those electrolytes.

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Although hydration is of the upmost importance for athletes, Ely also warns against over hydrating. “In the past there were issues with athletes in long distance races that had gotten advice that you cannot drink too much water and were drinking so much that they were diluting their serum sodium and causing a condition called hyponatremia. So they were basically over hydrated and when you lose that sodium balance, it can cause things like brain swelling and neurological detriment, which can be fatal. It is possible to drink too much water, and another one of the challenges is that the symptoms can be confused with dehydration, so if the person doesn’t know they’re over hydrated and goes to drink more, they can get themselves in trouble.”

The most important thing is to recognize the role that hydration plays in an athlete’s performance. Yes, under hydration and over hydration are each possible; however, if you focus on maintaining your fluid levels before, during and after exercise, the level at which you perform will be compromised in the slightest.

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