The Dangers of Dehydration

“When you’re working out, you’re more likely to be losing water, both through your breath and through sweat,” says Renee Melton, MS, RD, LD, director of nutrition for Sensei, a developer of online and mobile weight loss and nutrition programs. “If you start out dehydrated, you won’t get a good workout. You’ll get dizzy, lethargic, your muscles won’t work as well, you won’t feel as sharp mentally, and you’ll get cramps sooner.”

That’s because water helps your body to exercise efficiently. It lubricates your entire body — without it, you’re like the Tin Man without his oil. It’s a vital part of the many chemical reactions in the body. “If these reactions slow down then tissues heal slower, muscle recovery is slower and the body is not functioning at 100% efficiency,” says Trent Nessler, PT, DPT, MPT, managing director of Baptist Sports Medicine in Nashville.

The Benefits of Adequate Water

By contrast, a well-hydrated athlete feels stronger and can work out longer and more effectively. “The heart does not have to work as hard to pump blood to the body, and oxygen and nutrients can be transported more efficiently to the muscles you’re working during exercise,” Nessler says. That means you’re going to have more energy, and the same exercises you struggled with when dehydrated will seem much easier.

But research has found that even experienced athletes don’t do a very good job at estimating their fluid needs. In one study, seasoned runners participating in a 10-mile race drastically underestimated how much sweat they lost and consequently drank too little to stay well hydrated. The runners underestimated their sweat losses by an average of 46% and their fluid intake by an average of 15%, resulting in the runners replacing only 30% of their fluids lost through sweat.

How Much Water Do You Need?

So how much water should you drink before, during, and after a workout? First, make sure you’re well hydrated to begin with. Drink fluids throughout the day before you exercise. Then follow this formula from Melton:

• One to two hours before your workout, drink 15 to 20 ounces of water
• 15 minutes before you begin, drink between 8 and 10 ounces of water
• During your workout, drink another 8 ounces every 15 minutes.

Can You Drink Too Much Water?

It’s possible to drink too much water, but difficult to do. There is a condition called hyponatremia, usually found in endurance athletes. With hyponatremia, the blood becomes excessively diluted from too much water and sodium levels drop to dangerously low levels. This can lead to nausea, headaches, confusion, fatigue, and in extreme cases, coma and death.