By Featherstone Nutrition / December 31, 2021

How-To: Master Your Hydration Plan

We all sweat. Some a lot more than others.

We all get salty crusty. Some with much more visible salty sweat rings than others.
Hydration is one of the most personalized elements in sports nutrition. There is no one-size-fits-all recommendation. It varies so dramatically from person to person and is very hard to predict without some cold, hard science. So let’s nerd it out –
Basics of Hydration & Sweat
Water is the largest constituent of the human body. It is essential to maintaining optimal physiological function and health. Our body is made up of 10-12 gallons of water. Water is a transporter of all the nutrients in our body. It eliminates waste and toxins. It lubricates our joints and organs. And thankfully for us athletes, it dissipates heat through sweat to help us regulate our body temperature during exercise.
The DRI (dietary reference intake) for water is 2.7 L for women and 3.7 L for men per day. This includes water from all beverages (except alcohol) and liquid in food. So, they estimate that 80% of your water comes from fluid, the rest from food. I’ll do the math for you – this is where the 8 cups for women and 10-12 cups for men per day originated. It’s important to note that these recommendations are based on the ‘median intake of generally healthy people.’ We athletes are certainly considered generally healthy but our sweat losses can greatly increase these needs.
We lose not only water but electrolytes in our sweat as a consequence of thermoregulation during exercise. In order to fully rehydrate, we need to replace not only the fluid lost but electrolytes as well.
There are two important elements to master your own personal hydration plan – knowing your sweat rate and sweat composition. 
Step One: Calculate Your Sweat Rate
A simple calculation can help you determine the amount of sweat you lose per hour during exercise.
Once you know how much you’re losing per hour, you can begin to calculate a plan for fluid on training runs, rehydration, and race day.
Your sweat rate may change related to weather (temperature and humidity), effort level, altitude, and physical condition status. It’s definitely worth the time to calculate your sweat rate for different conditions.
Step Two: Understand the Impact of Dehydration
For many athletes, it is a delicate balance between drinking and performance. Drink too much and you can risk stomach sloshing, GI upset, and hyponatremia (if you’re only drinking water.) Don’t drink enough and your performance suffers due to increased perceived exertion, higher heart rate, reduced blood volume, increased core temperature, decreased sweat rate and increased rate of muscle glycogen usage.
All of these things are truly a performance buzzkill. Relying on thirst isn’t a great idea because we don’t feel thirsty until we are already 1% dehydrated. And, at just 2% dehydrated our physical and mental performance begins to suffer.

Avoiding dehydration during a race is an important goal. But don’t forget about staying hydrated on a daily basis during and between training sessions. In a busy life filled with intense training sessions, it’s easy to overlook adequate hydration and over time dehydration can really sneak up on you and you’ll see your performance slowly start to decline.
Step Three: Perhaps You Need an Analysis of Your Sweat Composition
Many factors influence the electrolyte concentration in our sweat. As fitness improves, so should our electrolyte retention. In other words, an unfit person will usually lose more electrolytes than a very fit person. Another factor is heat acclimatization. If you trained all winter long in the cold, and race day was an unseasonably warm day, you could expect to lose more electrolytes in your sweat. Size may matter, as larger athletes tend to sweat more. However, there is also a large genetic component to sweat composition too.
The variability of sodium lost in sweat is huge. It can range from negligible to more than your daily requirement of sodium in just one hour. It’s not uncommon for endurance athletes to lose 3-8 grams of sodium in a 3 hour race. That’s 3-5 times your daily requirement of sodium or 1 1/2 to 4 tsp of salt.
If you are continually depleting your sodium stores throughout your training and not adequately replacing these losses, performance will suffer.
*1 L of sweat = roughly 2# sweat loss 

Several companies have been offering sweat composition testing at the elite and team level for years. Championship collegiate football teams routinely analyze their players sweat composition, conduct daily weigh-ins & weigh-outs, and develop detailed hydration plans. Gatorade Sports Science Institute has conducted series of sweat composition tests on elite endurance athletes to maximize athletic success and achievements. Now, this analysis is available on an individual level – mailed right to your house – for us all to fine tune our training.
After much research, I decided to contact Levelen, a leader in sweat testing for all athletes. My results and takeaways can be seen below. Please note: I was given a discount for my sweat testing but I was not paid for mentioning them. And, all opinions are solely my own. If you are interested in completing a sweat test, let me know. I have a discount code I can share with you. Again, no kickbacks to me. Just sharing the love!

Step Four: Nail Your Rehydration & Recovery
For every pound you lose, you need to drink 20 oz of fluid to fully replace this. Each pound lost represents 16 oz of fluid, however we need a little extra to rehydrate. It’s not a perfect system. Need to rehydrate more quickly between training sessions? Up that to 24 oz per pound lost.
Sodium is needed to adequately rehydrate. This can come from a sports drink with sodium or high sodium foods plus water. Add some carbohydrates into this mix to maximize your rehydration even further. Remember: this can be achieved through a combination of fluids and foods that works best for you.
Contact me anytime for help, advice, or suggestions to nail your hydration plan 24/7.
Who May Benefit from a Sweat Test

  1. Heavy sweaters – especially those who participate in triathlons, marathon and ultramarathons, football, cycling, basketball, rugby, tennis, or other sports with padding in the heat.
  2. Salty sweaters – you know who you are. As the sweat dries, you’re left with salt rings on your body and clothing.
  3. Endurance athletes looking to individualize and optimize rehydration between training sessions and to perfect race day hydration.
  4. Athletes experiencing muscle cramps. Muscle cramps are a complex phenomenon but the first culprit to rule out is a hydration component.
  5. Those following a low sodium diet for health reasons. If you are following a low sodium diet, say 1500-2000 mg per day, and avoiding extra salt while training – you can see that you will deplete your sodium tank very quickly.
Things I Learned from My Sweat Test
I have been interested in completing a sweat test for awhile now. Thinking back to my field hockey and lacrosse days in high school, (Truth: I didn’t put on a bib and run my first race until I was 25 and it was the Cleveland Marathon. Don’t recommend this btw.) I was the ‘sweaty’ one on the team who sweat through her jersey during warm-ups. I frequently got light headed during practice yet all I drank was water and no one told me differently.
I wish I knew then just a little of what I know now. But, that leads me to the sweet things I learned about myself from my sweat test and how it impacts my training.
  1. I am not nearly as ‘salty’ of a sweater as I thought. I am actually quite ‘average.’ I lose 950 mg of sodium per hour of running. Average losses for athletes is around 1,000 mg per hour. Another way to look at this is a 1/2 tsp salt an hour. Not a big deal for an hour of exercise, but if you’re looking at a 2 or 3 hour run or race – this adds up and absolutely needs to be accounted for in your fluid/food during races and training.
  2. I lose significantly more potassium than average – 265 mg per hour of running and the average is 50 mg. But, this is still only a 1/4 of the amount of sodium I lose per hour (950 mg.) To put this into reference, half a large banana contains the amount of potassium I lose per hour. Other good sources of potassium are apricots, coconut water, melon, dates, potatoes, beets, and beans.  Fun Fact: the Institute of Medicine recommends 4700 mg potassium daily. Most American’s barely reach half of this recommendation daily. 
  3. The weather (humidity and temperature) did not alter my sweat composition or rate. (I did two sweat tests one in hot and humid conditions and another in cool and drier conditions.) In fact, I lost slightly fewer electrolytes during the warmer and more humid weather. Riddle me that?! I feel confident knowing my hydration plan can hang tight regardless of the weather. I appear to lose about a liter of fluid per hour of running. 
  4. After 80 minutes of exercise, my body will reach the 2% dehydration threshold where performance tanks. My current personal ‘rule’ is carry fluids for runs over an hour – I’ll stick to this. It’s easier to rehydrate after a run when you’re not totally in the hydration hole.
  5. My husband is indeed a chemistry master. He converted mmol to mg of Potassium for me. Because my brain doesn’t comprehend mmol and DRI’s of nutrients – or really chemistry, anymore, for that matter. 
  6. If you’re interested in seeing what your sweat ‘looks’ like, contact me and I’ll share a discount code and help you interpret the information into your training, if you want of course! Again, I don’t get any kickbacks from this – I’m just ruthlessly passionate about helping others perform at their finest through nutrition and hydration. Or a huge nerd who likes to see other peoples sweat composition – you decide if that’s creepy or cool! Kidding. 
Rosenbloom C. Sports Nutrition: A Practice Manual for Professionals. 6th ed. Chicago, IL: SCAN Dietetics Practice Group, Academy of Nutrition and Dietetics; 2017.
McArdle WD, Katch FI, and Katch VL. Sports & Exercise Nutrition, 4th ed.  Baltimore, MD: Lippincott Williams & Wilkins, 2012.
Sawka MN, Burke L, Eichner R, Maughan RJ, Montain SJ, Stachenfeld N. American College of Sports Medicine. Exercise and fluid replacement position stand. Medicine and Science in Sports and Exercise. 2007; 377-390.
Clark N. Sports Nutrition Guidebook. 4th Ed. Champaign, IL: Human Kinetics, 2008.

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