The mercury is rising in the Northern Hemisphere which means the thermostat is cranked up, the humidity is high, and I should invest in Skratch Labs from the amount of Exercise Hydration mix I am consuming!  All joking aside, exercising in the heat is something all of us do, and this blog post will be my attempt to shine a little light on the ins and outs of exercise hydration.  First things first though, what is hydration?

Hydration is consuming liquids to maintain fluid homeostasis in the body.

So, think of hydration, or staying hydrated, as keeping the fluids in your body topped up by drinking.  Your body will maintain homeostasis of its fluids by signaling you to drink via thirst, or urinating when it has too much.

How Do I Know If I am Hydrated?

Knowing if you are hydrated is pretty simple, just look in the toilet after you urinate.  The urine should be clear, or a very pale yellow.  Anything darker than that means you should drink up!


What Should I Do If I Become Dehydrated?

Well, the simple answer to that question is drink something (duh)!  But, what that “something” is can make all the difference.  The ideal oral rehydration solution should be,  according to WHO and UNICEF, 6 teaspoons of sugar and 1/2 teaspoon of salt per liter of water (1).  BE WARNED, adding more sugar and/or salt to the mixture will change its osmolarity and make it less isotonic.  As the solution becomes less isotonic, your body will actually become MORE dehydrated because it will need to take fluid out of your cells to dilute the solution!  For this reason, I tell my athletes to drink their fluids and eat their calories, i.e. don’t drink your calories.  This is a very important concept to understand, so if that was confusing, check out this excellent video from Dr. Alan Lim explaining this concept a bit further:

How Do I Figure Out How Much To Drink?

Simple answer again, drink when you’re thirsty.  Thirst is an excellent indicator of your body’s fluid homeostasis and is a mechanism human beings have used since the beginning of time with a rather good success rate.  But, since this is a blog about exercise science and becoming a better athlete, optimal fluid intake is something we should discuss.  The easiest way to find out your optimal fluid intake is to perform a sweat-rate test.


Sweat Rate Testing

Performing a sweat rate test is rather easy, all that is required to do is to weigh yourself pre, and then again post-ride.  During the course of the ride, drink as you would normally. Also, be sure to be in your birthday suit for your post-ride weigh in.  Then, to calculate your sweat rate…

  • A = Weight lost during exercise, in ounces.
  • B = Fluid consumed during exercise, in ounces.
  • C = Length of exercise session.
  • Sweat Rate = (A + B) / C

For example: I weigh 140 lbs and decide to ride for 1 hour on a really hot and humid day whilst consuming 1 bottle (24 oz) of fluid.  After my ride, I weigh 139.5 lbs.  So, my sweat rate would be (8 oz +  24 oz) / 60 = 53 oz of fluid per hour.  I recommend doing this test throughout the course of the season and keeping a log to figure out how your sweat rate changes at 70, 75, 80, 85, etc. degree days.  Doing so will ensure you are optimally hydrating throughout your workout.

Hydration Strategies

Staying hydrated is all about drinking throughout the course of the day and especially your workout.  However, some athletes become excited during a race or hard group ride, or become fatigued mentally and forget to drink altogether.  Forgetting to drink spells disaster for your performance as a drop in body weight of 2% will begin to modify your work rate ability, while a drop in only 5% will decrease your work rate by 30% (2).  So, needless to say, keeping topped up on fluids is crucial!  Here are some ideas to make sure you keep drinking over the course of a long and hot ride…

  • Set an alarm on your Garmin to beep every 15 minutes.  Doing so will remind you to drink.
  • Change up the flavor of your drink on your long rides.  Doing this will prevent your tastebuds from getting sick of the same flavor.  Also, try to consume rather light tasting drinks, this will prolong the time before your tastebuds say no.
  • Pre-cool your body.  Doing this will lower your core temperature, draw-out the increase in your sweat rate, and allow your body to maintain its fluids.  This can be done by wearing an ice vest during your warm up pre-race, eating a popsicle or something else frozen, and/or putting an ice pack around your neck to cool your carotid arteries.
  • Keep your body cool during exercise.  Doing this will have the same effect as pre-cooling.  This can be accomplished by consuming cold fluids, wiping sweat away with a towel, and/or spraying cold water on your head and hands (a lot of arteries in those areas).
  • Know how many ounces your water bottles are.  This may seem obvious, but you would be surprised that most athletes do not know how big their bottles are.  Knowing this will allow you to optimally hydrate after figuring out your sweat rate.
  • Make sure you keep drinking after you are done exercising until you reach your pre-exercise body weight.  I recommend drinking 1.5x the amount of fluid weight you lost during exercise.
  • Follow the directions on the drink mix.  Remember, more is not better in this arena.  If you change the osmolarity of the solution you are drinking you will further dehydrate yourself!
  • Eat foods that are high in water throughout the day.  Doing this is an easy way to hydrate if you don’t feel like drinking a ton of fluid.  Think fruits and veggies.
  • Above all else, JUST DRINK!

Maintaining fluid homeostasis and developing an optimal hydration plan during exercise should be a part of evolving and maturing as an athlete due to the huge drawbacks of becoming dehydrated during training and competition.  Make sure you understand how much you need to be consuming by performing sweat rate tests throughout the year as temperature and intensity of the workout will modify it.  Ensure you are consuming a drink that is isotonic to actually rehydrate you.  Please don’t drink your calories.  And above all else, JUST DRINK!

Want the stuff GC Coaching athletes use and recommend?  Skratch Labs is where is is at!  Check them out here:


Shayne Gaffney

About the Author Shayne Gaffney

Shayne holds a bachelors degree in Health Science in Professional Development and Advanced Patient Care, is a licensed physical therapy assistant in Massachusetts, a USA Cycling Level 1 (expert level) certified Coach, a USA Cycling Power Based Training certified Coach, Precision Nutrition Level 1 certified Coach, a US Military Endurance Sports (USMES) affiliated Coach, and USA Olympic Committee Safe Sport certified. He is the owner and head Coach of GC Coaching, Workout Content Editor at Zwift, the creator of P2 Coached Computraining, and the creator of Zwift’s “Build Me Up” Flexible Training Plan. He has been published in Bicycling Magazine, the TrainingPeaks blog, and Zwift Insider. He can be contacted directly via


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