At first glance, hydration seems simple. We’ve all heard the same stale quips a million times: “Drink before you’re thirsty” “Pickle juice prevents cramps” “Avoid diuretics like excess caffeine and alcohol” “If your pee is clear, no need to fear” “If your pee is dark, urine trouble” Easy, right? Well, maybe not. If hydration was that straightforward, then we wouldn’t have elite athletes dropping out of races or nearly dying due to hyponatremia (an electrolyte imbalance caused by drinking too much water). We also wouldn’t see corporations spending millions of dollars to develop a better sports drink every year. In every edition of every endurance sports publication, there’s bound to be at least one story presenting new evidence or a groundbreaking research study about the intricacies and importance of adequate hydration. It can be a lot to absorb, as it were. To add to the confusion, some of the latest hydration research contradicts long-standing tenets. For example, in the past, athletes were advised to avoid drinks such as coffee, tea, and soda, due to the supposed diuretic effect of caffeine. However, to the resounding joy of java-fueled athletes everywhere, most exercise nutritionists now say that these beverages are safe to consume in moderation, and that they can only lead to dehydration when consumed in herculean quantities (though I daresay that on the nights prior to my college Physics exams, I often ventured dangerously close to that celestial limit).
Failure to hydate during exercise can lead to some pretty serious consequences. First, and *most* (read: least) importantly, it will slow you down. There’s evidence that losing just 2 percent of your body weight in sweat can significantly degrade performance. For a 150-lb triathlete, that’s only 3 pounds of sweat, or a little over a quart. The performance inhibiting effect of dehydration can be linked to a number of physiological mechanisms. Your body uses water to regulate temperature and cool itself down through sweat. But water is also necessary for other essential organs and processes, including carbohydrate metabolism and as lubrication and padding for tissues. When you lose too much water, your body diverts blood (i.e. water) from your muscles and and sweat glands to keep your interal organs - like your heart and brain - alive and well. As a result, your body releases less sweat, which makes your body temperature rise, which makes it even harder to keep your interal organs cool, which makes your body release less sweat, which makes your body temperature rise…. see where I’m going? Since your muscles are receiving less blood, they’re also more likely to cramp up and misfire. Chronic dehydration during training and racing has even been linked to a greater risk of injury. Finally, water helps things in the digestive system, er… move along. It’s been estimated that as many as 20% of gastrointestinal-related hospital visits - by normal people and sadistic multisport athletes alike - could have been prevented with just a couple glasses of good ole H two oh. Water also helps with the absorption of electrolytes and nutrients through the walls of your small and large intestines. When you don’t drink liquids along with those sugary, salty, sticky, candy-like gels (“nutrition”, in triathlete-speak), water must be pulled from your body to lower the sodium and glucose concentrations in your intestines before those molecules can be absorbed into your bloodstream and used to fuel your next training session.
On the other hand, drinking too much water can also be an issue. Proper hydration doesn’t just mean guzzling gallon after gallon of Adam’s ale. Athletes who do so can suffer from hyponatremia - which Latin speakers can tell you literally means “below normal sodium disorder.” It’s also known as “water poisoning”. The signs of hyponatremia are paradoxically similar to those of dehydration, much to the chagrin of race health staff who are responsible for triage. Hyponatremic athletes may show symptoms including headache, nausea, fatigue, and irritability (which, now that I think about it, is pretty much how I feel at the end of every race anyways), but in extreme cases it can lead to seizures, respiratory arrest, coma, and death. That got dark pretty fast, but here’s the bright side: to avoid hyponatremia, you need (read: get) to eat all the salty food! Pickles, pretzels, tomato juices, and many other sodium-laden foods that have been demonized by the American Heart Association are actually essential for triathletes who soak through more than more set of workout clothes each day. Sports drinks can also be a good source of sodium and other electrolytes including potassium, magnesium, and calcium. But be wary of marketing ploys involving athletes secreting unnaturally vibrant sweat: Gatorade and Powerade contain too much sugar and not enough electrolytes, which usually makes them a poor choice for rehydration. Instead, opt for endurance-sport nutrition brands like Hammer, Clif, Infinit, Skratch Labs, and Maurteen. Some of these products might cost a pretty penny, but you really only need them for workouts that last longer than 60-90 minutes. And they’re much cheaper than an ambulance ride to the ER.
The quick answer is “enough so that you’re never thirsty and your pee is consistently pale yellow.” The long answer requires a bit of math. You can use the technique below, or check out this nifty calculator: http://www.triharder.com/thm_swrate.aspx Just before you head out the door before your next workout, weigh yourself. Then keep track of how much fluid you consume during the workout. Finally, weigh yourself when you get back home. Plug those numbers into this equation: (your weight in lbs before a workout) - (your weight in lbs after the workout) + [(how many fluid ounces of water you consumed during the workout) / 16] = (your total fluid weight loss) Divide your total fluid weight loss by the workout time to get your hourly sweat rate. E.g.: Weight before: 150 lbs Weight after: 148 lbs Fluid ounces consumed: 16 Workout time: 90 minutes (1.5 hours) 150 — 148 + [16 / 16] = 2 + 1 = 3 lbs Cool, right? And yes, also a little gross. You can use that formula to figure out how much to drink during and after a workout in order to replenish your fluid loss.
Sodium can be a bit more tricky. You could head to a “Sweat Testing Clinic” (yes, they exist) and pay hundreds or even thousands of dollars to run on a treadmill in front of strangers wearing starchy white coats. Or, if you’re not interested in paying to play lab-rat for a day, or finding out what a “Sweat Testing Clinic” smells like, just experiment yourself. Try out different sports drinks (most are also sold in single-use packets), slowly introduce more salty foods into your pre- and post-workout meals, and see what works for you. If you’re craving pepperoni pizza with a side of dill pickles after every ride, it might be a sign that you need to add a dash of salt to your morning oatmeal, or bring another bottle of sports drink next time.
Caffeine and diuresis during rest and exercise Hydration and physical performance Water, Hydration and Health The Economics of Dehydration Diagnosis and Treatment of Hyponatremia Individualized hydration plans improve performance outcomes https://www.ncbi.nlm.nih.gov/pubmed/29866199 Sweating rate and sweat sodium concentration in athletes https://www.ncbi.nlm.nih.gov/pubmed/28332116
Will Krakow is a mathematician with a writing problem from Chapel Hill, NC. He qualified for the 2017 70.3 World Championships (but gave up his spot to attend Oktoberfest), owns a 12:09 beer mile PR, and has won the local group ride sprint exactly one time. In his spare time, he enjoys long runs on the beach and candlelit trainer sessions.