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7 Common Signs of Exercise-Induced Dehydration & What You Can Do About Them

If you do any type of prolonged, intense physical activity, you’ll want to know how to recognize exercise-induced dehydration. Why? Staying properly hydrated is one of the most effective things you can do to maintain peak performance and mental sharpness.

Luckily there are a few telltale signs of dehydration that don’t require any fancy lab tests, blood draws or urine samples. Rather, you can spot them just by paying attention to your body.

Dehydration occurs when you loss 1% or more of your body weight as fluid and you don’t replace it.1 For example, a 150-lb soccer player who sweats as little as 1.5 lbs (about 3 cups) of fluid during a game and doesn’t properly rehydrate would be mildly dehydrated. But dehydration is a slippery slope. It can go from mild (a loss of 1% to 2% body weight as fluid) to severe (6-10% loss). As it becomes more severe, symptoms become more pronounced.

Here’s a breakdown of seven common signs of dehydration:

1. You’re thirsty

We’re hardwired to be thirsty. This behavioral urge is primarily stimulated by receptors that sit just outside the blood-brain barrier. They’re called osmoreceptors, and they monitor the water and electrolyte balance of plasma (also known as plasma osmolality). As plasma osmolality rises, our sense of thirst increases, which drives us to drink fluid and replenish body water.

The body is good at triggering thirst, and it doesn’t wait until things are out of whack. In fact, one meta-analysis2 of 12 clinical trials shows thirst is typically triggered when plasma osmolality is in the middle of the normal range. For this reason, most healthy people can use their sense of thirst as a reliable regulator of fluid needs and a good guide for the need to rehydrate.

2. Your urine is dark in color and low in volume

You can gauge your hydration status by monitoring the color and volume of your urine. When you are properly hydrated, your urine is pale to straw color. By contrast, when you are dehydrated, it’s darker in color (like the color of apple juice) because it’s more concentrated. Plus, your urine volume is reduced because your kidneys are working overtime to reabsorb water to prevent further loss.

3. Your skin is dry and less elastic

When you’re properly hydrated, your skin has good turgor. This means it’s plump, resilient and bounces back when you pinch it. On the other hand, when you are dehydrated, you lose skin turgor. The result is dry skin with little or no elasticity.

Skin turgor is easy to measure by pinching a fold of skin, preferably over your sternum or on your inner thigh. If you’re well hydrated, your skin will immediately fall back to its normal position when you release it. If not, it may be a sign that you are dehydrated.

Since skin naturally loses elasticity as we age, the skin turgor test is less reliable in older people. A good alternative that’s independent of age is tongue turgor. In a well-hydrated person, the tongue has one, long narrow furrow. By contrast, a person who is dehydrated will have additional furrows.3

4. You experience headaches

Dehydration can result in a headache. Researchers have yet to confirm the exact cause, but some speculate that the most likely cause is intracranial dehydration. This affects the membrane surrounding the brain (the meninges) and results in pain. The brain itself may also be affected since other symptoms such as impaired concentration, nausea and irritability have been reported with a dehydration headache.4

5. You get muscle cramps

An exercise-associated muscle cramp, also known as EAMC, is a painful muscle spasm that occurs during or soon after activity. (You would be hard pressed to find an athlete who hasn’t experience one of these at one time or another.) It’s unpredictable and can be intensely painful, but thankfully temporary.

Exercise scientists have yet to confirm the exact cause of EAMCs. Some believe dehydration is involved because it disrupts water and electrolyte balance. Others point to altered neuromuscular control that triggers an abnormal muscle reflex. Likely, EAMC is a result of a combination of factors.

To see if your muscle cramps are associated with dehydration, consider keeping a cramp journal or add muscle cramps to the factors you track in your current exercise journal. In this way, you can uncover any link between when you’re dehydrated and muscle cramps.5

6. Your mental sharpness is impaired

Everyone responds differently to dehydration, but as a rule of thumb, you’ll likely have more difficulty staying mentally sharp when your fluid loss is 2% or more of your body weight, particularly in hot weather.

Mild dehydration has been reported to alter several mental functions like reducing your ability to stay focused and alert and may even sour your mood. Moderate dehydration takes a bigger toll, potentially impairing your ability to perform tasks that require short-term memory, perceptual discrimination, math ability, visual tracking and motor skills.6

7. Your physical performance is compromised

A relatively mild level of dehydration (a fluid loss is in the range of 2% of body weight) can compromise your physical performance. As a result, you lose the ability to maintain optimal endurance. You may feel more fatigued and less motivated. Your perceived effort seems harder.

Plus, dehydration reduces blood volume, so it can lower blood pressure and reduce blood flow to the brain. This could result in feeling lightheaded.

These dehydration effects are seen mostly with high-intensity, endurance activities like tennis and long-distance running and, to a lesser extent, with anaerobic activities like weight lifting or shorter-duration activities like rowing.

It’s not uncommon for athletes, soldiers, and others who engage in prolonged, intense physical activities to lose up to 10% of their body weight in sweat loss. This is a severe level of dehydration. If fluids and electrolytes are not properly replenished, it can lead to a low heart rate (tachycardia), a weak pulse, and other adverse outcomes that may require medical attention.6

Your action plan to stay hydrated

Now that you know the common signs of exercise-induced dehydration, here’s a no-fuss plan to help you stay hydrated before, during and after activities.

With this plan, you can avoid sugary, acidic sports drinks that can damage your teeth. You can avoid the dangers of overhydration. And, you can avoid spending an arm and a leg for fancy, often cumbersome, products when all you need is sound science in the form of plain water and a well-designed electrolyte tablet.

Here’s how:

You’ll want to start your activity hydrated. To do this, nutrition experts recommend that you drink about 2.3 to 4.5 milliliters of water per pound of body weight about 2 to 4 hours before your activity. So our 150-lb soccer player would drink about 12-23 fluid ounces of water. To help you retain the water you drink, take Replace® Electrolyte tablets as directed.*

You’ll want to stay hydrated during your activity. To do this, drink up to 16 fluid ounces of water for every pound you lose per hour. (You’re goal is to just replace sweat loss.) For activities longer than 3 hours, you may need to redose with Replace® Electrolyte tablets.

You’ll want to rehydrate after your activity. Drink about 20 fluid ounces of water for every pound lost and take Replace® Electrolyte tablets to help rehydrate fast.* 

Taking on the demands of your active lifestyle is tough, but it’s a whole lot easier when you know the common signs of dehydration and how to avoid them.


  1. Benelam B, Wyness L. Hydration and health: a review. Nutr Bull. 2010;35:3-25.
  2. Hughes F, Mythen M, Montgomery H. The sensitivity of the human thirst response to changes in plasma osmolality: a systematic review. Perioper Med. 2018;7:1. https://pubmed.ncbi.nlm.nih.gov/29344350.
  3. Shepherd A. Measuring and managing fluid balance. Nurs Times. 2011;107(28):12-6. https://pubmed.ncbi.nlm.nih.gov/21941718.
  4. Blau JN, Kell CA, Sperling JM. Water-deprivation headache: a new headache with two variants. Headache. 2004;44(1):79-83. https://pubmed.ncbi.nlm.nih.gov/14979888.
  5. Maughan RJ, Shirreffs SM. Muscle Cramping During Exercise: Causes, Solutions, and Questions Remaining. Sports Med. 2019;49(Suppl 2):115-124. https://pubmed.ncbi.nlm.nih.gov/31696455.
  6. Popkin BM, D'Anci KE, Rosenberg IH. Water, hydration, and health. Nutr Rev. 2010;68(8):439-58. https://pubmed.ncbi.nlm.nih.gov/20646222.