Why dehydration can crush any workout – and how to fight it

Senior woman hydrating during workout

During my last exercise class, my trainer yelled, “I hope you guys hydrated before you came. I will be able to tell who did and didn’t.” How the heck could he know who had a glass of water before class? As it turns out, water has a significant role in how strong you are during training.

Working out produces sweat, and the more sweat you produce, the more dehydrated you can become. Dehydration can cause fatigue and muscle cramps, so it is no surprise that a well hydrated body can perform better.

Symptoms of dehydration

Common symptoms of dehydration include:

  • Weakness
  • Fatigue
  • Agitation
  • Muscle cramping in the arms and legs
  • Nausea
  • Dizziness

If you are really thirsty during a workout, you are probably already dehydrated or almost there. It is important to drink water not only when you are exercising but before and after as well. The American College of Sports Medicine recommends the following hydration plan for exercisers.


  • Drink 16–20 ounces of water at least four hours before exercising
  • Drink 8–20 ounces in the 10–15 minutes before your workout


  • Drink 3–8 fluid ounces of water every 15–20 minutes when working out 60 minutes or less
  • Drink 3–8 fluid ounces of a sports beverage (5–8 percent carbohydrate with electrolytes) every 15–20 minutes when exercising greater than 60 minutes


  • The amount varies based on weight and amount of fluid lost during exercise
  • General estimate is 20–24 ounces per pound lost

Clearing up confusion

Water bottleA common misconception is that muscle soreness the day after a workout is due to lactic acid buildup and drinking extra water can help flush it out of your system and reduce pain. However, experts say excess lactic acid typically leaves your body within an hour after a workout. Post-workout soreness is called DOMS—an acronym for delayed onset muscle soreness. This is actually caused by putting too much strain on your muscles during exercise.

The peak of DOMS is usually about 48 hours, and swapping ice and heat on the sore muscle can help with the pain. Talk to your trainer about stretches and adding more strenuous activities in increments to reduce the impact of DOMS.

Still, it is never a bad idea to drink extra water in the days following exercise to replenish the fluid you lost—and to prepare for your next workout.

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