Dehydration Effects on Athletic Performance

In this episode we're going to talk about dehydration effects on athletic performance. Dehydration decreases mental and physical performance both on the field and in school in dramatic ways. Not staying hydrated, for example, cut performance by nearly 50% in laboratory studies for patients who were just walking!

Dehydration affects the body and the mind in many ways that extend well beyond the soccer field. Listen to find out how dehydration decreases mental performance in school, decreases endurance, and can lead to significant medical problems.

Dehydration effects on athletic performance

What's the problem?

One study I read showed that 70% of high school football players were dehydrated before practice even started. This affected not only their performance on the field, but also in school, and had a significant negative impact on their health. A strong correlation exists between hydration and learning performance - both in the sports environment and in school. It turns out, our brains and even our immune system needs plenty of water too!

Water makes up 50-65% of the average athlete's body weight. When we're dehydrated, it's kinda like driving a car without oil. The lack of proper hydration for lubrication, circulation of blood (for thermal regulation and nutrient distribution) makes it difficult for our bodies and brains to function, and that leads to early fatigue. 

What are the general effects of dehydration on athletic performance?

Dehydration creates the following conditions:

  • Reduction in blood volume (blood flowing around the body)
  • Decreased skin blood flow (meaning we can exchange heat efficiently in the cold or the heat) Think about the radiator in your car.
  • Our core temperature goes up
  • Decreased sweat rate
  • Increase rate of muscle glycogen use (our muscles burn sugar faster) which leads to fatigue

When thinking about the general effects of dehydration on athletic performance, it helps to know that these effects are compounding. As our core temperature goes up, for example, stress on the body increased, which increases the demand for more "coolant" water. 

Performance test results

Let's look a little closer at the effects of dehydration on athletic performance. In a study referenced below in the resources section, scientists took a group of subjects through a test. The asked each of them to complete a 140 minute walk. In the table below, you can see the results of that test in terms of completion rates. 

Dehydration %

Completion Rate


3% Dehydrated


Everybody completed 140  mins

5% Dehydrated


12% could not complete the test

7% Dehydrated


75% stopped after 64 minutes!

When subjects were dehydrated to 8%, they were only able to complete only 55 minutes of the test. This should speak volumes about the effects of dehydration on athletic performance!

Emergent effects of dehydration

Dehydration is well known for creating additional, more obvious effect on athletic performance and on our well being. If left untreated, this progression can lead to hospitalization and even death. Conditions like heat exhaustion and heat stroke might be in your athlete's future if we're not watching for the warning signs such as:

  • Headache
  • Thirst
  • Muscle cramps
  • Weakness
  • Nausea 
  • Irritability
  • And even goosebumps!

It's important to remember that athletes are going to dehydrate even further from wherever they start activities like practices and games. So if an athlete shows up already 3% dehydrated, they can be 5-7% dehydrated by the end of the activity. Remember that our hydration status changes along the way. At the end of a practice or a game, for example, our athletes can be in pretty bad shape if they started off dehydrated in the first place. 

Being dehydrated also reduces out ability to tolerate high core temperatures and it reduces maximum cardiac output. This means the heart can not pump as much oxygen and fuel delivering blood around the body.  At a systemic level, dehydration also:

  • Decreases plasma volume (at rest and during activity)
  • Decreases blood volume
  • Decreases blood thickness
  • Lowers central veinous pressure
  • Lowers the return of blood to the heart for resupply
  • Decreases the ability of the heart to "re fill" with blood so that it can push out the maximum stroke volume

Dehydration presents a vicious cycle. Blood carries sugar to the brain - which is what the brain uses for food. Without this brain food, the brain will slow down and not be able to solve problems as quickly. Players who are not thinking clearly in a thinking person's game like soccer are definitely not contributing to their full capacity!

When and how to hydrate

Drinking before and after after athletic activity or a practice is critical. The National Federation of High School Coaches published the following guidelines in a course they offer titled Sports Nutrition: 

  • 15-20 ounces of fluid 2-3 hours before a competition or a practice (sports drinks are about 20 ounces and also have electrolytes and sugar needed)
  • Drink during stoppages of play (especially during half time - cold beverages are better)
  • Replace 1.5 times the weight lost through sweat. 15-30 ounces of fluid within 30 minutes of training or a match
  • Drink 1 liter or 2 quarts of fluid every few hours after the activity

I have my kids start to hydrate the day before a practice or match. This is to give the body time to completely hydrate. The opposite of this is slamming 20 ounces as they're walking onto the field. The slam method of hydrating just leads to stomach sloshing, cramps, and the need to pee. If, on the other hand, we start 24 hours in advance, our cells can be exposed to the fluid longer and plump up nice and juicy.

Think about dropping a raisin in a 50 gallon drum. If you pull that raisin out 30 seconds later, you just have a wet raisin. If, on the other hand, you drop a raisin in a shot glass of water and let it set overnight, it'll be nice and plump in the morning. 

Avoid caffeinated drinks, soda, power drinks, or alcohol. All of these beverages can have the opposite effect that we want. They can make us pee more. And sugary soda drinks are just bad for our bodies anyway. 


Invite others to Join our Community!

The Soccer Sidelines

Soccer Dad, Coach, and Club President who is devoted to developing kids and their families. With a diverse background in leadership in other settings, David is focused on empowering parents, players, and coaches to focus on the stuff that really matters in youth sports.