Fitness, Nutrition, Tennis

How to Calculate Your Average Workout Water Loss

You know you’re supposed to stay hydrated, but do you know how to calculate your average workout water loss? Every time you hit the gym, your body loses water. Since your body is 65 percent water, being dehydrated by as little as 2 or 3 percent can decrease performance by as much as 10 percent. Depending on your diet, hydration habits, and the intensity of your workout routine, you are more or less prone to sweat out an unhealthy percentage of water…

Now, you might be saying to yourself: “But what’s wrong with sweating a lot? I thought I was sweating off the pounds!”

It’s a common and dangerous myth that dripping sweat will drop the pounds. In fact, sweating too much can be counter productive. When you work-up a dripping sweat, your body starts to lose heat. Millions of sweat glands lying under your skin go into overdrive, consuming metabolic energy in order to secrete all the sweat. Your total energy, in effect, gets drained; and, in effect, energy is drained from your muscles… The very muscles you are trying to strengthen! 

Here’s how to calculate your workout water loss, so you know if you’re staying safely hydrated:

1. Weigh yourself before working out (For example, we’ll use a nice, round number: 200 pounds)
2. Weigh yourself immediately after working out (For example, 195 pounds)
3. Subtract the post-workout weight from the pre-workout weight (5 pounds lost)
4. Divide the pounds lost by the pre-workout weight (5/200 = .025, or 2.5% weight loss)
5. Lastly, multiply the pounds lost by 15.3, or the number of fluid ounces lost from the body for every pound lost during workout (5 pounds x 15.3 fluid ounces = 76.5 fluid ounces lost)

So, what do all these numbers mean? They mean if you weighed 200 pounds pre-workout and 195 pounds post-workout, you would have lost 2.5 percent of your body weight, and 76.5 fluid ounces of water. You might feel good about losing 5 pounds, but even at 2.5 percent body weight loss, your performance would have already degraded by a decrease in thermoregulation and a steady increase in thirst.

Negative effects on your workout performance only build alongside the percentage of weight loss. At 4 percent, your energy is now limited by 25 to 40 percent. At 5 percent weight loss,headaches are common, as well as a feeling of weakness, incoherence, fatigue, and general irritability. At 6 percent, you would feel especially weak, nauseous, and suffer from a dangerous loss of thermoregulation. Finally, at 7 percent and above, you would be in incredibly dangerous territory. Someone weighing 200 pounds would have to drop 14 pounds during a single workout in order to lose 7 percent of their body weight, which amounts to 214 fluid ounces of water, or over 26 glasses of water (assuming you drink 8 ounce glasses)! Obviously this is an extreme case, but you get the point…

You don’t have to sweat up a storm to shed the pounds. If anything, all that sweat may be slowing you down. If you stay well-hydrated, your post-workout weight loss should read close to 0 percent, which means you have enabled your muscles to workout under optimum performance conditions, unlimited by metabolic energy drain from over-sweating and fluid loss.

If you don’t want to workout the math on your own, don’t worry. Unlike working out at the gym, there are shortcuts with math, and online you can find many exercise water loss calculators.