Calculating Your Sweat Rate

author : NickSuffredin
comments : 1

What should you do if you train in hot weather and you sweat a lot? Do you drink more water, more sports drink...what about electrolyte supplements? Use this guide to enhance your training.

By Nick Suffredin and Mike Ricci
D3 Multisport.com

What should you do if you train in hot weather and you sweat a lot?  Do you drink more water, more sports drink...what about electrolyte supplements?  I find that It is ideal to stay with a sports drink as you do need the carbohydrate for those times/distances on the workouts/races.  However, you do need to find one that works for you.  There are some "lighter" sports drinks either in flavor or "sugars", but ideally for optimal performance a 3-6% carbohydrate-electrolyte beverage is needed to be consumed when exercising over 60 minutes, especially in the heat. 

If you are a heavy sweater, does your clothes become caked in salt (salt lines) after your workouts?  If so, you are most likely also a very salty sweater.  Typical athlete's salt losses range between 500-2000 mg of sodium, plus additional electrolytes (sodium being the one of mass/critical loss).  When a athlete has a high sweat rate they will usually have a high sodium/electrolyte loss as well. 

Salt pills would possibly be a wiser move vs. just adding "water" or diluting your sports drink.  When you dilute your sports drink, you're also minimizing the amount of electrolytes you are consuming per serving as well which again doesn't help you out.  The electrolytes are multifaceted.  Electrolytes will initiate the thirst mechanism to encouraged drinking, they will replace the electrolytes lost in sweat which will help mitigate muscle cramping from dehydration, and they also help maintain fluid balance in the body which allows you to hold more fluid in. 

To dial in your fluid loss and help give you an idea of where your electrolytes should be, perform a sweat test on yourself.  A sweat test is best done in the same temperature that you’ll be racing in and done at your run race pace –Half Iron, or Ironman. Start the test by weighing yourself in the nude. Once you have completed running race pace for one hour, you’ll towel yourself off and weigh yourself in the nude. If you drink any fluids during your run, make sure you account for those. Our goal is going to be at a 2% loss of body weight or less. If you are over 2%, then you’ll have to replace fluids to keep loss at 2% (or less).

If you're closer to a >2 Liter/hour sweat rate than you're likely at 1000 mg or more of sodium loss an hour as well.  

CALCULATE YOUR SWEAT RATETo begin, record your nude body weight prior to exercising.  When you are finished exercising, dry yourself off the best you can and record your nude body weight again.  Record what and how much you consumed of fluids during your exercise.  Subtract your post-exercise weight from your pre-exercise weight and add the amount of fluid you consumed to that number.  This will give you the amount of fluid you lost while exercising at that sport.  Then you need to divide that number by the amount of hours you exercised for and that will equal your sweat rate.  Be sure to record the weather conditions as well, as to see how this may fluctuate. 

1. ________ Record your nude body weight prior to exercise.

2. ________ Record your nude body weight (dry off best you can before recording weight) after exercise (convert weights to ounces; 1 lb = 16 oz).

3. ________ Record how much fluid you consumed during exercise (use ounces).

4. ________ Subtract lines 1 & 2 from above for total weight loss and add line 3 (Line 2 - Line 1 +Line 3).  This is the amount of fluid your body lost while exercising.

5. ________ Take the number from line 4 and divide it by how many hours you exercised for.  This will give you and idea of what your sweat rate is.

The total formula is: (Line 1 - Line 2 +Line 3)/Line 4

Now the tricky part is if you are losing a ton of fluids, how to manage that. I’ve seen people lose 4-6 pounds in an hour of running! That’s an awful lot of fluid to replace. So, the key in this instance isn’t replacing all the fluids but learning what supplements you need in order to stop losing all that weight. Typically most of us can get away with 2 bottles an hour along with 750mg of sodium per hour. My suggestion would be to do the sweat test, then see how much you need to replace. If it’s more than 48 ounces per hour, I would take in two Salt Stick tablets per hour as well.

Should I perform a sweat test for BOTH the bike and run?

It's really ideal to do a sweat test during a run, as it involves your total body and effort.  It will give you a more ideal gauge of your actual sweat rate based on your totally body being active.  However, if you are looking for sport specific, then yes, your sweat rate will vary slightly between disciplines.  Thus, you will be able to determine the differences of hydration needs between the disciplines.  There is a caveat to that though in real world settings (outside of a lab). 
 
When I ask athletes to do a sweat test, it is always on the run.  There is less variables to factor in in terms of cooling effect/local climate (i.e. wind), which allows for it to be more accurate.  I then use that estimated sweat rate to base their fuel strategies and hydration plans.

You'll have to experiment with your nutrition plan, but it is best you consult with a sports nutritionist regarding this plan. 


Nick Suffredin was formerly a scientist at the Gatorade Sports Science Institute where he worked on testing elite professional athletes to enhance their hydration practices and nutrition intake to improve their performance.  Currently, Nick provides fueling and hydration strategies working with D3 Multisport.

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date: September 25, 2014

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