Skip to main content

Tough Workouts? You Could Be Dehydrated

Water makes up over two-thirds of the human body. Yet, we lose water from our bodies every day through sweating, breathing, using the restroom, and through our tears and saliva. That’s why it’s important to replenish your body by drinking enough water.

If you’re losing more water than you’re taking in, you can become dehydrated. "Dehydration is when the amount of water in your body falls below a normal, heathy level,” says Traci Thompson, MS, director of PEAK Health & Fitness at University of Utah Health. Staying hydrated is especially important being, during, and after exercising.

Why is dehydration harmful?

“Dehydration impairs your body's ability to regulate heat, which causes your body temperature and heart rate to rise. This causes you to feel more tired during exercise,” Thompson says.

Dehydration also weakens your mental function. This can negatively affect your motor control, decision making, and concentration. When your body is dehydrated, your stomach also passes food into the small intestine more slowly than normal. This can cause your stomach to hurt.

All of these differences in your body can reduce your performance during exercise.

How to Prevent Dehydration

"If you drink regularly during exercise, you can prevent the worst side effects of dehydration,” Thompson says. “Drinking enough water will prevent a decline in your concentration and skill level."

Drinking the right amount of water can also:

  • Prevent your heart rate from rising
  • Prevent body temperature from rising
  • Improve performance during exercise

How much fluid do I need?

Your body needs different amounts of water before, during, and after exercise. 

  • Before exercise: Drink one cup of water at least four hours before you start exercising.
  • During exercise: Drink 4 to 5 ounces (120-150 ml) of water every 10-15 minutes.
  • After exercise: Drink enough water to double the amount of water your body lost during exercise.

How can I tell if I’m dehydrated?

One of the easiest ways to tell if you’re dehydrated is to look at the color of your urine—it should be a light color, not dark.

But if you’re scientifically-minded, you can actually measure how much water you should drink after you exercise using the weight test.

Here’s the simple formula:

  • Weight (before exercise) — weight (after exercise) = fluid loss

So, if you weigh 150 pounds before exercising, but weigh only 148 pounds after exercising, you have lost two pounds of water weight.

To replace the amount of water your body has lost: Drink 24 ounces of water (3 cups) for each pound lost.

You can be sure not to sabotage your workouts by staying hydrated.