After a typical training session, most athletes are somewhat or very dehydrated, according to research published in the Journal of the International Society of Sports Nutrition. But when athletes followed a personalized hydration plan, tailored to their average fluid and sodium loss, they were able to exert more anaerobic power (that’s what you tap into to lift, sprint, and jump), recover faster, and improve attention and awareness. That’s just from having the proper amount of water and electrolytes.
Now, the athletes in this study were doing two-a-days or six-day training weeks, so they were sweating a lot. And the workouts their personalized hydration plan helped were anywhere from 60 minutes to two hours long. Researchers found relying on thirst alone may not be sufficient to rehydrate your body.
While participants reached for water the same number of times when they were drinking based on thirst versus the personalized plan, it’s the amount of fluids they drank as well as the composition that made the difference.
“For the personalized plan, we provided them with a guide for fluid intake—not too much, not too little—and adjusted the electrolyte composition of this fluid to match the electrolyte composition of their sweat,” says lead study author Michael Corcoran, Ph.D., assistant professor of health sciences at Merrimack College in Massachusetts.
It’s still unclear if the improvements were thanks to a greater amount of fluid or a better electrolyte balance in their water, but either way, the men performed better and hydrated more efficiently when they followed a personalized plan during their intense workouts.
And depending on your sweat loss and your workout intensity, a personalized plan might help your performance, too.
How Hydration Affects Performance
It’s harder to train with full-throttle intensity when you’re dehydrated. Your body has less water, which means less blood volume, so your heart has to pump more vigorously, upping your heart rate. Your core temperature is also warmer, so your metabolism is a bit less efficient. Overall, you have to work harder to achieve the same performance result, Corcoran says.
But in order to replenish water, you have to replace electrolytes—the chemicals (namely sodium) you lose with sweat. Electrolytes help your body take up both glucose (fuel) and water more efficiently. That makes these molecules crucial to neuromuscular functioning. And research is starting to show even mild electrolyte depletion may subtly affect an athlete’s nervous system, causing their reflexes and reaction time to be slower, regardless of their carb energy stores, Corcoran adds.
Why Sports Drinks Aren’t Always Enough
“Most people lose between 0.5 to 1.5 liters of sweat per hour, but sweat loss can vary dramatically from person to person. It’s highly dependent upon factors like workout intensity and the climate,” Corcoran explains. Bigger dudes produce more sweat, for example, and the more fit you are, the harder you’re pushing during any given workout, so you’re sweating more than the average guy.
But there’s also a genetic component to it. Some people just sweat more than others, and some lose more sodium per drop.
In fact, research in the Scandinavian Journal of Medicine & Science in Sports found that among marathon runners, some had lower levels of electrolytes in their blood even after refueling with the same amount of water and salt as other runners. This is where a personalized hydration plan comes into play.
Do You Need a Personalized Plan?
A personalized hydration plan has two components: quantity (how much fluid you’re losing under certain conditions) and quality (what exactly you’re losing: namely sodium chloride or salt).
Whether or not you need one all depends on how active you are.
“The average fit guy who goes to the gym or participates in short events, like a 5K road race, does not need to get a sweat test. Drinking to thirst is more than sufficient,” Corcoran says. “But sweat testing may be advantageous for athletes who engage in very hard, prolonged training for several hours or days.” This can include triathletes, marathoners, and ultramarathoners.
Those who fall in between—half-marathoners and those who perform intense training four days a week—might benefit if they’re experiencing side effects common to dehydration, like fatigue, weight loss, cramps, elevated heart rate, or heat illness, he adds.
Although, let’s be clear: Not all endurance athletes need to get a sweat test.
“I actually think going by thirst helps avoid problems associated with overhydration that a lot of endurance athletes can fall into,” says Shawn M. Talbott, PhD, Utah-based exercise physiologist and nutritional biochemist. He’s referring to the nausea, weakness, drop in blood pressure, and even seizures that can happen as a result of hyponatremia, the clinical name for overhydration that affects some 10% of triathletes as well as other distance athletes. (Learn more in How Drinking Too Much Water Can Be Life-threatening for Endurance Athletes.)
That said, Talbott contends a sweat test could potentially be useful for athletes suffering stomach or muscle cramps, or having GI issues late in a competition—all signs they aren’t getting enough fluids. Mostly that’s endurance runners and triathletes, but potentially also serious soccer players or anyone going hard for a longer period of time and feeling physiological pushback from their body.
The hard-and-fast rule: If your workouts are under an hour, you’re fine to drink plain water when thirsty. If you’re sweating for more than an hour regularly, replenish electrolytes and water. If you’re working for upward of 90 minutes at a reasonable intensity (i.e., not just a two-hour walk), consider a personalized hydration plan, especially if you have cramping or GI issues late in the game.
How to Get Tested for a Personalized Hydration Plan
Remember, a plan has two components: how much fluid and how much sodium you’re losing.
You can determine the first part yourself. Weigh yourself naked immediately before an average workout, train, track how much fluid you drink, then weigh yourself naked immediately after.
“A 2% body weight loss means you’re dehydrated,” Corcoran says. That is, your thirst mechanic is not sufficient to keep you hydrated. There’s not an exact ratio of how to replenish based on your loss, but more on that in a sec.
If you’re consistently weighing in at 2%+ less post-training, or you just love quantitative data and have a few hundred to blow, you can get a sweat test to determine your average sodium loss (some even cost $200-$300). It’s a harmless process: a machine analyzes a patch that’s been on your skin. (You can try a company like Precision Hydration.) The main thing is to work with a knowledgeable coach or trainer who can explain what your sweat sodium value means and how to apply a strategy afterward.
Whether you get a sweat test or just try the naked-on-the-scale strategy, use the results as a baseline and then track how you’re responding to the intervention of more fluids, both Talbott and Corcoran agree. Good signs: fewer muscle cramps, less GI distress, more energy late in the game. Red flags: You’re dashing to the porta-potty at every mile marker of a race—a sign you’re overhydrating and entering dangerous territory.