Fluid Facts....How (much)?

I’ve covered the “who”, “what”, “where”, “when”, and “why” of hydrating for exercise, so now we get to the final question:

“How much?”

There is no one universal answer to this question. Several factors affect how much fluid you need: the amount of time you’re on the bike, the weather, the type and amount of clothing you wear, your weight, your body’s ability to acclimate to different weather conditions, and your genetics—meaning some people are just genetically programmed to sweat more than others.

Estimated baseline fluid needs for endurance cycling are as follows:

• Before cycling (within approximately 2 hours before getting on your bike), drink 16 ounces of fluid.
• During cycling, drink 8 ounces every 15 minutes. Over the course of 1 hour during the time you're riding, at least half of that fluid should come from a sports drink to replace electrolytes.
• After cycling, drink 16 to 24 ounces within approximately 1-2 hours.

These amounts are a good baseline, but remember that you’ll need to bump this up when it’s hot or if you feel you are sweating more than usual.

You can determine your specific baseline fluid needs for exercise by measuring your "sweat rate". Here’s how it works:

1. Weigh yourself, wearing little or no clothing, before exercise.
2. Fill your water bottle and measure exactly how much fluid is in the bottle.
3. Then, exercise vigorously in controlled environmental conditions (such as on a treadmill inside or a Spin bike). Be sure to also monitor the length of time you exercise (ideally, approximately 30 minutes for this test.)
4. After exercising, weigh yourself, again wearing little or no clothing (We don’t want the weight of the sweat still trapped in your clothing to be measured.) Do not urinate until after you weight yourself.
5. Subtract your after-exercise weight from your pre-exercise weight. Your weight before exercise minus your weight after exercise=weight lost due to fluid lost through sweat and evaporation in the respiratory tract. (Weight lost during exercise is not “true” weight loss, but simply represents a fluid deficit during that exercise period.)
6. Measure how much fluid is left in your water bottle and determine exactly how much fluid you drank.
7. Every 1 pound of weight lost during this time period of exercise represents a 16-ounce fluid deficit—this is how much you need to add to the amount you drank during exercise to achieve adequate hydration.

To illustrate:

• Before a 60-minute Spin class, a cyclist’s weight (wearing little or no clothing) is 150 pounds. For this one class, she does not drink any fluid. After class, she weighs herself (again wearing little to no clothing) and her weight is 149 pounds. During class she drank 14 ounces of fluid.
• Her 1-pound weight loss during exercise represents a 16-ounce fluid deficit. The 14 ounces she drank during the 1-hour class was 16 ounces less than what she needed.
• Her total fluid needs for 1 hour of exercise would be:

12 ounces (the amount she did drink) + 16 ounces (representing her fluid deficit determined by her weight change) = 30 ounces.

This gives her a baseline for her fluid needs per hour, but she will need to remember that this amount will be higher during hotter weather.

Another more quick-and-easy way to assess whether you are drinking enough fluid during exercise is to check the color of your urine. If it’s clear or nearly clear, you’re hydrating enough. If not, you need to be drinking more fluids.

How much water? How much sports drink? A good rule of thumb for most people is to drink half water and half sports drink. Using two water bottles (one for water and one for a sports drink) works well to stay on track. Or, some people make a cocktail of half water and half sports drink in each bottle.

Is it possible for you to drink too much? Actually, yes, if you drink too much plain water without any electrolyte replacement, you may put yourself at risk for a condition called “hyponatremia”. I have first-hand experience with hyponatremia, and I’ll tell that story in my next post so you can learn from my mistakes. :o)

Until then, ride on!

Shelley