Yep. That's about how it can feel sometimes after a discussion of hydration math. With the drought and the fires in Texas, I thought I'd take a moment to put a few words in on this very important subject. While not everyone needs to worry about it during a race, everyone should be considering their hydration status during other times. Proper hydration is important because it can affect your performance, helps lubricate your joints, helps your body recover, and even affects cognitive function. There is so much that proper hydration does for us, that to list it here would take away from the intent of my post.
Let's start with how much fluid you lose during a training run. I'll use an example from a discussion held a few months ago...
First, a important message from our sponsor, Water. Water equals a little more than 8 pounds per gallon, so 1 pound is about 16 ounces... Keep in mind, the math gets a little fuzzy and I round for simplicity and to eliminate decimals.
Say you're a 155 pound athlete that went for a 8 mile run in 100 degree heat, you drank 24 oz of water and it took you 81 minutes. Weigh yourself naked before your run. Then weigh yourself after your run, also naked. For our example, you lost two pounds. 155-153 is 2 pounds of hydration loss. 24 ounces of water taken in is about a pound and a half. Add that together and you lost roughly three and a half pounds of fluid. 3.5 divided by 8 miles is .4375 pounds of fluid. A calculator helps me find (16 oz per pound, so 16 times .4375) that .4375 pounds of fluid roughly equals 7 ounces per mile of fluid loss. I prefer the per mile measure rather than per minute because it tends to be more constant through the different speeds we run and easier to figure than using per minute.
So, you lost 7 oz per mile of fluid through sweat, exhalation and other normal body functions. This is good to know. But these numbers may change as the weather changes, as your exertion changes, and even as you become a more finely tuned athlete. So, for endurance athletes, weight is your best measure for hydration information, and as you get more familiar with this method, you'll be able to predict where you'll be.
Okay, so I lost a billion ounces of water on my run this morning. Now what?
Now, you replace it. Not at once, but gradually. Evidence shows that your body can process about a liter of water per hour. If you drink more, you risk affecting your electrolyte balance. Want to your body to get the most use of that expensive bottled water or sports drink? A liter per hour, max.
So what does that mean for me?
It's all weight based. The minimum amount of fluid you drink every day should be one half your body weight (pounds) in ounces of fluid every day. So, if you still weigh 155, then you should start by drinking 78 ounces a day. Then, you went out and ran for 81 minutes. Replacing fluids by weight lost is the preferred method. If you know how much weight you lost during a workout, attempt to replace that much fluid (16 ounces per pound) in addition to your minimum daily intake. Since in our example, you lost 2 pounds, drink at least 32 ounces of water (at a liter per hour).
If you don't know how much weight you lost during a workout, start with the following formula:
Hours of training x 32 = total fluid. Total hours of training is how long you should spend rehydrating following this method. In our example, you ran for 1.3 hours, so drink at least 42 ounces of fluid at a liter per hour.
Real life application (in a bubble)
Now it's time to apply the formulas. You got up and ran this morning, as soon as you got up. You weigh 155 pounds, so you need to drink a minimum of 78 ounces a day of fluids. You lost 2 pounds during your workout, so you need to replace 32 ounces of fluid (16 oz per pound), but don't forget the 24 ounces of fluid that you drank during your workout. 78 + 32 + 24 = 134 ounces of fluids.
I want to point out that recent research points to sports drinks, certain teas, juice and other fluids being acceptable for hydration. Caffeinated drinks aren't the hydration nemesis they were once thought to be. However, hydration math has its limits, as it cannot predict sweat rates in different weather conditions, differences in individuals and other wrenches that get thrown into the works. Your best gauge is the color of your urine. If you are peeing clear to light yellow, all signs point to well hydrated.
Having said all the above, you'll need to find out what works for you.
I also want to mention sodium. I've spent several years researching, practicing and seeing what works for ME. You'll need to find out what works for you. Don't forget potassium, calcium and magnesium either-these are also crucial to proper electrolyte balance, proper muscle contraction/release, and for life.