Avoid Dehydration on Hot Runs

Five ways to prevent dehydration and replace lost electrolytes when the sun won’t let up.


I have a confession to make. I can’t stand summer running. I can’t stand the heat, the humidity, and the fact that I’ve had to stop and walk during short runs that are usually effortless. I long for I can’t-feel-my-toes, tights-clad winter runs as I suffer through sunburns and salty, sweaty, dehydrating summer runs. Sure, there may be some scientific benefits of training in the heat, but as I trod along and pray for snow, I’m not interested. What I am interested in is staying as well hydrated as possible (dehydration means slower times, which means even more minutes out in the heat). But maintaining euhydration, or a normal state of body water content, is not as easy as it seems for those of us who arrive home caked in salt after a long summer run. There is good news, though: by following some of the tips below and trying out some of the products mentioned, you’ll be more likely to stay hydrated, whether you’re reading this as you slather on the sunscreen this summer or while donning layer upon layer of clothing this winter.
1. Don’t get behind in the first place. Just as there are many ways and means to take in fluids (water, sports drinks, and water-containing foods all come to mind), there are many different ways to determine adequate hydration. While some of these involve expensive laboratory and medical equipment, there’s an easy and cheap way to check approximate hydration status from the comfort of your own bathroom. By simply noting the color and volume of your urine you can gauge whether you need to drink more (or maybe less). Dark-coloured urine of a relatively small volume is an indication of dehydration and should signal you to drink more fluids throughout the day or during your run.
2. Hydrate before heading out. In general, consider following this recommendation adapted from The American College of Sports Medicine’s Position Stands. Exercise and Fluid Replacement: Drink approximately 30ml per every 5kg of body weight four hours before running, and if profuse sweating is expected, drink ~17ml per every 5kg of body weight 2 hours before a run. Give yourself time to use the bathroom before you head out.
3. Establish a game plan. While some experts recommend you stay hydrated by simply drinking when thirsty, others suggest you develop a customised plan by performing a sweat test. To stay better hydrated during long, hot runs (or even windy, frigid runs, for that matter), you need to perform a sweat test. Weighing yourself before and after exercise is the most effective way to gauge your fluid needs. Any weight loss corresponds with fluid loss, so try to drink enough to replenish that weight. (Weight gain could mean you are drinking more than you need.)
4. Recognize your losses. Electrolytes are lost both in sweat and in urine. Some athletes lose a lot of electrolytes while others don’t, and there’s wide range of the amount lost. As you can see in the table below, sodium and chloride are lost in larger amounts than potassium, magnesium, and calcium, as well. The values listed represent the amount of electrolytes contained in a litre of sweat. Keep in mind that individual athletes lose varying amounts of sweat, so use the table below as a ballpark reference.
Mineral  Concentration in Sweat (mg/L of sweat)
Sodium  460-1840
Chloride  710-2840
Potassium  160-390
Magnesium  0-36
Calcium  0-120

Table adapted from Sports Nutrition: A Practice Manual for Professionals, 5th Edition. 


5.  If you replace sweat losses during the run, research shows that you’ll better optimise cardiovascular, thermoregulatory and performance responses.  Use your sweat test results to determine how much fluid you need each hour.  If you’re going for a leisurely run or a run that lasts less than an hour, you can stay hydrated with water every few kilometres.  If you’re a salty sweater, cramp-prone or going longer than an hour, you might want try adding some electrolytes to your water.  There are a few options out on the market, and a select few are listed in the table below.  If you’re going for a long and taxing run, you might want to opt for a carbohydrate-containing sports drink rather than water and electrolytes alone.

  • Gatorlytes  780mg of Sodium, 400mg of Potassium; Comes in a pouch to add to water or Gatorade
  • Pedialyte 244mg of Sodium, 294mg of Chloride, 183mg of Potassium; comes in ready-to-use 1L bottle, 6.8oz carton, powder packs to add to water, and freezer pops
  • Nuun 360mg of Sodium, 13mg of Calcium, 25mg of Magnesium, and 100mg of Potassium; comes in multiple flavored tablets to add to water
  • Hammer Nutrition Endurolyte 40mg of Sodium, 60mg of Chloride, 50mg of Calcium, 25mg of Magnesium, 25mg of Potassium, Vitamin B6, Manganese, and L-Tyrosine; Comes in a capsule of power to chase with or add to water
  • Salt Stick 215mg of Sodium, 22mg of Magnesium, 11mg of Potassium, and 63mg of Vitamin D; Comes in a capsule to chase with or add to water
  • Mio Fit 75mg of Sodium, 35mg of Potassium, and Vitamins B3, B6, and B12; A concentrated liquid to add to 8oz of water

One more thing: Proper use and dose of these products vary.  Be sure to check manufacturer websites and product labels for details on how to safely use the product.  And don’t forget to perform your own sweat test, listen to your body and consider the amount of electrolytes already present (or not) in your diet.




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