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A Triathlete’s Guide to Hydration and Electrolytes

By Katie Rhodes | July 25, 2016, 5:47 p.m. (ET)


It’s a no-brainer that hydration and electrolyte supplementation are extremely important during these hot months. Although this is a well-known fact, the topic is often dreaded by coaches and registered dietitians when approached by clients because there is no straightforward answer without addressing different internal and external variables. Like carbohydrate supplementation during endurance activity, hydration and electrolyte supplementation can vary from person to person depending on factors such as length and duration of activity, clothing, environmental conditions, body composition and genetics. An interview is required to better pinpoint needs, as well as experimentation and journaling. Let’s look at the basics of hydration needs and electrolyte functions and then we can better understand how to determine individual needs.


Hydration is crucial during exercise, especially exercise lasting more than 1 hour. When we are not working out, fluid is primarily excreted from the body through urine. When we are exercising, fluid excretion shifts largely from urine to sweat (note to athletes who do not consume adequate fluid before and during exercise in fear they will have to frequently stop for bathroom breaks). Because there are many factors affecting sweat volume, weigh yourself before and after exercise throughout the year as your climate changes. Journal your findings to pinpoint differences based on environmental factors and note trends in fluid loss. To replace fluid, replace 1 pint (16 ounces) of fluid for every pound lost. If you are losing 2 percent body weight or less you are replacing correctly. If you are losing more than 6 percent body weight you are at a greater risk for heat exhaustion, heat stroke, severe heat cramps and even coma or death.

To start determining your needs, start with a goal of 24-32 ounces an hour. Calculate the weight change and start your workout already hydrated. How do you know you are hydrated? Your urine is a pale yellow. Do not rely on thirst to determine when to consume fluids, but determine your specific needs and drink at regular intervals throughout exercise. I recommend every 15-20 minutes.

Math lesson: Jim, currently weighing 180 pounds, recovered from a heat stroke he experienced two weeks ago after his long Saturday ride. Previously he consumed fluids only when he was thirsty and now wants to determine how he can replace fluids correctly. After cycling for 4 hours he weighs 176.4 pounds, a 2 percent weight loss (3.6 lbs. weight loss/180 lbs. starting weight=0.02 or 2%). Jim wants to determine what a 6 percent weight loss would be in order to gauge how well he is hydrating himself, so he does the math: 0.06 (6%) x 180 lbs. is a 10.8 lbs. weight loss, or 169.2 lbs. His goal is to be the same weight after exercise as before and to stay away from 169.2 lbs!


The following ions are electrolytes: sodium, chloride, potassium, magnesium, calcium, phosphate and bicarbonate. Electrolytes and water go hand in hand: where there is a high concentration of electrolytes, water follows, so both need to be replaced during exercise. This is because electrolytes need water to conduct electricity regulating hydration, muscle and nerve function and acid-base balance. Pertaining to athletics they also improve cognitive function, performance, reaction time, muscle cramp frequency and recovery. Through my research I noted that consuming branch chain amino acids (BCAAs) and arginine/glutamine supplemented the effectiveness of these results. The primary electrolytes lost in sweat are sodium and chloride compared to potassium, magnesium and calcium.

Knowing the concentration of electrolytes each athlete needs to replace during exercise is not as easy to determine as fluid needs. Just as you should start exercise hydrated, you need to start exercise with electrolytes in your system. This can be consumed through a salty snack or a beverage containing electrolytes, like Gatorade. What to consume during exercise depends on the intensity and duration. Typically you do not need to start replacing electrolytes until about 1 hour after starting. After 1 hour, add electrolytes to your water or consume in the form of food. Companies have come up with some great products that contain electrolytes and others that contain a combination of electrolytes and carbohydrates, either in the form of fluid or food. Experiment what works best for you by consuming different forms of the three elements you need when exercising: water, electrolytes and carbohydrates. Consult with a registered dietitian to guide you through the process of finding which forms work best for you and in what amounts.

Katie Rhodes, owner of OWN-Nutrition, is a registered and licensed dietitian in Little Rock, Arkansas, with a Master of Science in clinical nutrition. Through her experiences training elite athletes and working in the clinical setting at Arkansas Children's Hospital and the Central Arkansas Veterans Association, Rhodes understands that what we are putting in our bodies directly affects our performance, quality of life and longevity. She's worked with triathletes for six years on their nutrition year round as well as focusing on race day nutrition. Rhodes primarily works with clients remotely, through phone calls and Skype for communication, to supplement unique, personalized nutrition plans.

The views expressed in this article are the opinion of the author and not necessarily the practices of USA Triathlon. Before starting any new diet or exercise program, you should check with your physician and/or coach.