Hydration is key to sports nutrition success

What is the big deal about hydration?

A hydrated athlete is a healthier and more productive athlete. Even small drops in body fluid levels can have a negative impact on your health and performance. For a 120# woman, dehydration starts with as little as a 1# weight loss. Therefore, fluid goals are important in your sports nutrition plan!

Early signs of dehydration begin with lack of concentration and increased body temperature (1% body weight loss), then progress to decreased performance (3% weight loss), to cramps, chills, nausea, and a rapid pulse (5% weight loss). More danger comes with headaches, dizziness, stomach cramps, which are characteristic of heat exhaustion (>5% weight loss). Heat stroke includes increased body temperature, no sweat or urine, dry tongue and an unsteady walk. Seek medical attention in these latter stages of dehydration. It’s no joke…dehydration is dangerous.

Are there any simple ways to test for dehydration?

Other than having your blood drawn, two tests you can do on your own include the urine color check and the weight check. First thing in the morning, check the color of your urine. It should be pale (light in color like diluted lemonade or straw). If it is yellow-gold (like apple juice) or darker, you are dehydrated. (Some vitamins cause urine to be a bright glow-in-the-dark yellow. This unnatural color is not related to your hydration).

The other test is to check your weight before and after a workout/event. Ideally, weigh yourself first thing in the morning after you go to the bathroom and before you drink or eat anything. Hydrate as usual before and during your training, making note of the number of ounces you drank between weigh-ins. After the session, weigh yourself without clothes again. Do this caculation:

Sweat Rate Calculation to Customize Your Fluid Needs

(start weight in pounds X 16 to get your weight in ounces) minus (ending weight in pounds x 16 to get your weight in ounces) plus (number of fluid ounces you drank) minus (estimated ounces of urine you released between weigh ins) = (weight change in ounces, which will be ounces gained or ounces lost in the session).

Example:
Start weight 150 pounds (or 2400 ounces)
minus End weight 147 pounds (or 2352 ounces)
equals 48 ounces (3 pounds weight lost between weigh ins)
Drank 16 ounces between weigh ins, so add 16 oz. + 48 oz.= 64 ounces
This is the "net" loss (the scale shows 48 oz. lost, but you really lost 64 oz. since you replaced 16 oz. of it already).

Common sense at this point should tell you that you lost weight during the workout and didn't drink enough. So, the goal is to drink more next time you do a comparable workout.

How do I use this result to know how much I should drink when working out in similar conditions?

Take (weight change in ounces) divided by the (number of minutes of your training session). This will give you your estimated "sweat rate per minute". Your sweat rate is used to determine how many ounces you should be drinking per minute of a typical training session. For example, if you lost 3 pounds (48 ounces) in a 120 minute workout session, drank 16 ounces of fluid and did not urinate between weigh ins, your weight change is 64 ounces. Over 120 minutes, your sweat rate is .53 ounces per minute (64 divided by 120). Now, .53 x 60 minutes means you need to drink 32 ounces per hour (8 ounces every 15 minutes). You'll want to do this test several times to get an average sweat rate for the season you're in.

Obviously, if you weigh with clothes and don't keep track of your fluid intake and urine output (tough to do in the woods or at the porta potty) the results will be less than accurate. However, you should still weigh yourself before and after training as often as you can. You'll get the general idea if you are losing or gaining weight which then relates to if you are under- or over-doing it with fluids.

Can't I just go by how much I sweat?

No. How much a person sweats depends on genetics, physical training level, temperature, humidity, wind, and type of clothing worn. Sweating is a good thing. The purpose of sweating is to release internal heat. You may find that as you get in better shape you start to sweat sooner--this is good, but all the more reason to stay in tune to your body's hydration level and your fluid habits. If you are dehydrated you don't sweat as well. The resulting build up of internal heat is where the danger comes in.

What do I do if my weight changes during a training session or event?

Body weight changes at the conclusion of a training session or event are hydration changes, not fat loss (fat loss occurs over a longer period of time). Your goal is for your finishing weight to be about the same as your staring weight, give or take a few ounces. If you lost weight, a general rule is to replace 20-24 ounces of fluid for every pound lost. This amount includes your make-up needs and your current needs. This could be a lot to replace, so it is best to hydrate before and during an event to maintain your fluid levels, with maybe only a slight need to catch up afterwards. A goal is to have your weight return to normal within 6-8 hours of the training session/event. If you gained weight, you drank too much, and should adjust (reduce) your intake during the next training session.

The last point is to never rely only on thirst as a hydration indicator…thirst is not always accurate. However, if you are thirsty and have dark colored-urine and/or weight loss, dehydration is likely.

What if I gain weight during the workout?

Unless you ate at a buffet along the trail, you gained water weight. You should not gain weight from fluids during a workout as this could put you at risk of water overload (sometimes called water intoxication or medically called hyponatremia). The problem with water overload is that this dilutes the sodium level in your blood. A normal sodium level is needed to keep your body fluid levels in their place. Water intoxication may begin with headaches, and can lead to brain swelling and eventual death. It is more commen in women, likely related to estrogen and our design of starting with less fluids in our body. A diet with ample sodium is wise during endurance training, but managing your fluid intake is very important. Keeping track of your pre- and post-workout weight and listening to your body is key and something you can control.

Check out how to use sports drinks , how to time your fluid intake (before, during and after an event) , and general principles of hydration in everday sports nutrition and fitness.

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