Dehydration Effects on Sports Performance -Image of football player with leg cramp

Dehydration Effects on Sports Performance

Hydration is especially important for athletic performance. Thirst cues can be unreliable, and dehydration effects on sports performance can be noticeable when you lose as little as 2% of your body weight from water (1) (2) (3).

Maintaining Water Balance for Peak Performance

Water balance

To maintain water balance, the water you drink will equal the water you lose.

  • Water intake = Water Loss


Dehydration occurs when you take in less water than you lose.

  • Water intake < Water Loss


Hyperhydration, or over hydration, is when you take in more water than your body loses.

  • Water intake > Water Loss      

This is generally not a problem.  It can be beneficial to have a little extra water when exercising, but be aware. Extra water can lead to an increased urge to use the restroom.


Hyponatremia, or low sodium in the blood, can occur with excess fluid intake. This can happen if you sweat a lot, and only replace fluid lost with water versus water with food or sports beverages that have electrolytes. This is most commonly seen in ultra-endurance athletes.

Image of scale balance water intake vs. water loss - Maintaining Water Balance for Peak Performance

What Factors Impact Water Loss

Your body is ~60% water (4). You lose water when you breathe, through skin pores, when you go to the bathroom, or when you sweat.

On a daily basis, most water is lost through urine, but up to 90% can be lost from sweat if you are exercising in warmer weather (2).

Other factors that can impact water loss include body temperature, fitness level, heat, altitude, cold temperature and more. These factors will be discussed in this article.

Body temperature

Physical activity increases the body’s temperature. When your muscles contract, the heat generated is twenty times hotter than when you are at rest (3).

Sweating helps to support a stable internal body temperature of ~98.6 degrees Fahrenheit, or 37 degree Celsius.

Body Temperature - Image of a thermometer

Fitness level

Just starting to exercise?  You may lose more water through sweat.


Increased environmental temperature leads to increased water loss through sweat

Heat - Image of outside thermometer


Higher altitudes can lead to dryer air and the increased likelihood of water loss. There is less oxygen at higher elevations. This naturally increases the number of breaths you take per minute, which leads to increased water loss as you exhale.

In addition, you may experience more rugged terrain at higher elevations. This can lead to increased heat and sweat as your body does more work.

Altitude - Image of a mountain top

Cold Temperatures

Cooler temperatures may lower sweat rates, but this is not guaranteed if you are wearing heavy layers.

Percent Water Loss and Dehydration Effects on Sports Performance

During physical activity, it is normal and healthy for your body to sweat to keep cool. As you continue to lose water, there is a reduction in blood volume. This means your muscles are receiving less oxygen and fuel over time. 

As you lose more water, your body will begin to show various signs of dehydration that can negatively affect sport performance and your overall well-being. A few signs of dehydration include increased heart rate, elevated body temperature, reduced ability to concentrate, and an increase in glycogen use by the muscles (3).

The affects of dehydration on sports performance may vary by individual, but here is a breakdown of the common symptoms at each point of dehydration.

Table: Percent Body Weight Water Loss

1% Body Weight LossThirst
↑ heart rate
2% Body Weight LossDehydration
↑ thirst
↓ mental clarity
↑ body temperature
↓ physical performance
3-5% Body Weight Loss↓ blood volume
↓ 2% in muscle strength
↓ 3% in muscle power
↓ 10% in high-intensity endurance
6-8% Body Weight LossHeadache and dizziness
↑ body temperature
↑ heart rate
↑ breathing
9-12% Body Weight LossMuscle cramps
Reduced Performance
Inability to Concentrate
Irrational Behavior
Renal failure
Dehydration Effects on Sports Performance – References: (3)  (2)  (1)  (5)

1% Body Loss

  • Thirst cues occur when your body fluids (including blood volume) become more concentrated. You may experience one percent body weight water loss before you are triggered to drink. 
  • One percent water loss leads to an increase in heart rate of three to five beats per minute (3) (2) (5).

2% Body Loss

  • 2% body water loss is the definition of dehydration
  • Thirst cues will continue to climb
  • Mental clarity will decline
  • If you are active in warmer weather, physical performance may worsen
  • Body temperature will rise (2) (3) (5).

3-5% Body Loss

  • Decreased blood volume
  • 2% Reduction in muscle strength
  • 3% reduction in muscle power
  • 10% reduction in high-intensity endurance (1) (3) (5).

6-8% Body Loss

  • Headache and Dizziness
  • ↑ body temperature
  • Increased heart rate
  • ↑ breathing (2) (5).

9-12% Body Loss

  • Muscle cramps
  • Nausea
  • Vomiting
  • Headache
  • Dizziness
  • Confusion
  • Disorientation
  • Weakness
  • Reduced Performance
  • Inability to Concentrate
  • Irrational Behavior
  • Renal failure
  • Death (3) (5).
Image of table shown above - % Body Weight Loss and Dehydration Effects on Sports Performance

Final Thoughts on Dehydration Effects on Sports Performance

Water is a key factor in sports performance. Not only does water help to regulate your body temperature, but it is a major element of your blood, which aids in fuel delivery and waste removal (2).

With as little as 2% body weight loss from water, sports performance can worsen. For someone weighing 170 pounds (77.2 kg), a 2% water loss would be equal to 3.4-pound (1.54 kg) water weight loss. Making up for this amount of water lost during physical activity can be extremely difficult.

Understanding your personal needs can help you build a hydration schedule to limit dehydration effects on your sports performance.

For more information about The Dietitian Resource, visit our site or check out the blog.  Thanks for visiting!


1. Karpinski, Rosenbloom. Sports Nutrition: A Handbook for Professionals (6th edition). Chicago : Academy of Nutrition and Dietetics, 2017. ISBN: 978-0-88091.

2. Fink, Heather H., Burgoon, Lisa A. and Mikesky, Alan E. Practical Applications in Sports Nutrition (Sixth Edition). Sudbury, MA : Jones and Bartlett Publishers, 2021. 9781284181340.

3. Clark, Nancy. Nancy Clark’s Sports Nutrition Guidebook (6th edition). Champaign, IL : Human Kinetics, 2020. ISBN: 978-1-4925-9157-3.

4. Medicine, Institute of. Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC : National Academies Press, 2005. 0-309-53049-0

5. Mahan, Kathleen L. and Raymond, Janice L. Krause’s Food & Nutrition Care Process (14th edition). St. Louis, MO : Elsevier, 2017. 978-0-323-34075-5.

Leave a Reply

Your email address will not be published. Required fields are marked *


Most Popular:

More About Rochelle

Rochelle Inwood MS, RDN, ACSM EP-C

Hello there! I’m Rochelle Inwood, a Registered Dietitian Nutritionist (RDN) and Exercise Physiologist (ACSM EP-C). With over 14 years of experience, I have sharpened my expertise through diverse roles, including weight management program co-coordinator, patient/employee gym supervisor, outpatient dietitian, program manager, dietetic internship preceptor, and more. I am passionate about learning, creating, teaching, and supporting personal growth and development.