Dehydration hurts performance, right?
Pro stage racers ride so hard that their guts can’t absorb enough fluid to replace all that they are losing in sweat. Race rules also restrict when a rider can get a bottle toward the end of a stage. Although somewhat dehydrated, the pros sprint quite well!
For decades marathoners raced 26.2 miles in both cool and in hot conditions without drinking.
In 2013 ultra-stance swimmer Diana Nyad (63 at the time!) vomited regularly during a 110-mile swim from Cuba to Florida. She was sufficiently dehydrated that she received IV fluid afterward. Yet she swam very well, maintaining a steady stroke rhythm for the full 53 hours.
Proper management of hydration and electrolytes is important in both hot and temperate conditions. Scientists are learning more and more about hydration, electrolytes and sports hydration management. It’s becoming clear that much of what we were taught in years past is outdated – yet numerous myths about hydration persist. Here are an even dozen:
Hydrate or Die
The average male’s body is 60% water; the average female’s is 50%. The typical athlete has another 10% water because glycogen is stored with water. Obviously, if we don’t replace this, we die. However, almost all of the heat-related deaths every summer are shut-ins living in homes with no AC. Your body has about 2 quarts (liters) of free water in your intestines. You don’t even start to feel thirsty until you’ve lost 1.5 to 2 quarts of water!
More accurately: overhydrate, and you risk dying. Dilutional hyponatremia is a more serious problem than dehydration. That’s when you drink so much fluid that your blood sodium is diluted to a dangerously low level.
Dehydration Leads to Collapse
We’ve all seen pictures of runners collapsing at the end of a marathon or triathlon. Must be because the runner is dehydrated, right? Wrong. When an athlete stops, the runner’s pulse and blood pressure fall significantly so that less blood gets to the brain and the runner faints.
Dehydration Causes Cramps
Although pro cyclists routinely get somewhat dehydrated during races, we rarely read about cramps in the peloton. In lab experiments, dehydration has been shown not to cause cramps.
Drink Early and Drink Often
In the mistaken belief that dehydration affects performance and causes cramps, we have been taught to drink before a workout and to continue drinking frequently during the workout.
Instead, develop the habit of drinking enough throughout the day so that you are fully hydrated — you urinate every few hours with good output — but don’t force yourself to drink on the bike.
Drink Before You’re Thirsty
We’re also told to drink before we’re thirsty to be sure we take in enough fluid. Sports scientists now recommend drinking just enough to satisfy thirst in order to avoid hyponatremia. Your body is marvelously effective at self-regulating. If you are starting to get significantly dehydrated, then your thirst mechanism kicks in.
Water Is All You Really Need
Taste your sweat — does it taste like clear water? No! It tastes salty, as we all know.
In addition to replacing the water you lose in sweat, you need to replace the sodium. A liter of sweat contains about 800 mg of sodium — half the recommended daily intake of sodium — so after a sweaty workout don’t spare the saltshaker. A quart of your sweat also contains about 115 mg of potassium, only about 2.5% of the recommended daily intake of potassium!
Sports Drinks Provide All the Necessary Electrolytes
They provide some, but not all, to replace what you lose working out. The American College of Sports Medicine recommends that a drink contain 125-175 mg of sodium / 8 fl. oz. (237 ml) and 20-48 mg of potassium / 8 fl. oz. Most sports drinks don’t provide enough sodium, the one electrolyte you really need to replace. If they had enough sodium, they’d taste terrible. Read the ingredients on the label of your sports drinks – and supplement as needed.
Electrolyte Depletion Causes Cramps
If you cramp, you may have been told to eat a banana for potassium or to take Tums for the calcium, or to take a supplement for these electrolytes plus magnesium. The amount of each of these electrolytes in sweat is minute compared to your bodily stores, and depletion of them does not cause cramps. Experts disagree whether sodium depletion causes cramps.
Pouring Water Over You Is Effective
Your body cools itself like your car’s radiator cools your engine. Blood flows through your core organs, gaining heat, and then flows through your skin, producing sweat. Most of the cooling comes this way, not from your hot skin directly radiating heat to the already hot atmosphere. If you have limited water, drink it – don’t dowse yourself with it.
Carbonated Beverages Are Bad
Carbonated beverages are absorbed just as quickly as non-carbonated ones; however, carbonated drinks may make you feel full sooner so that you drink less.
Caffeinated Drinks Cause Dehydration
The amount of caffeine in a couple of cups of coffee or tea or 3 – 4 sodas isn’t enough to cause dehydration. If you need to urinate after drinking a caffeinated beverage it’s because of the fluid you ingested.
Beer Is Good for Rehydration and Glycogen Replacement
Unlike caffeine, alcohol — even in moderation — is a diuretic. Only about 1/3 of the calories in beer come from carbs (the source of glycogen); the majority are empty calories from alcohol.
The bottom line:
- Develop the habit of drinking frequently during the day and evening so that you are fully hydrated before exercise.
- During exercise drink whenever you are thirsty, but not more.
- After sweaty exercise, particularly if your clothes are white with salt, eat salty snacks.
Although there are many myths about hydration and nutrition, there are also facts based on current scientific research that can guide you this summer.
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- Cycling in the Heat, Part 2: – Hydration Management. 21 pages on assessing your personal sweat rate and composition, how much you should drink, electrolyte replacement and the pros and cons of electrolyte replacement drinks, supplements and foods.
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Coach John Hughes earned coaching certifications from USA Cycling and the National Strength and Conditioning Association. John’s cycling career includes course records in the Boston-Montreal-Boston 1200-km randonnée and the Furnace Creek 508, a Race Across AMerica (RAAM) qualifier. He has ridden solo RAAM twice and is a 5-time finisher of the 1200-km Paris-Brest-Paris. He has written over 40 eBooks and eArticles on cycling training and nutrition, available in RBR’s eBookstore at Coach John Hughes. Click to read John’s full bio.
Chris VandenBossche says
Great to see this. It’s time we catch up to the science. Cramps are caused by muscle damage, not dehydration. That’s why they occur when riders are making an unusually difficult effort–beyond what their muscles are accustomed to. You can hear a thorough discussion of the science on this episode of the Velonews Fast Talk podcast: https://www.velonews.com/2017/08/training/fast-talk-podcast-ep-26-cramping-myths-debunked_446593
What about cramps during platelets/plasma donations? This obviously has something do do with electrolytes/sodium/plasma levels, not muscle exertion/damage.
Interesting article about dehydration myths – thank you; however, it would’ve been even more interesting if it was supported by at least a few references (similar to Dr Mirkin style).
Mark Follmer says
Straight to the (bullet) point(s).
According to Dr. Tim Noakes, most of these myths were perpetuated by the sports drinks industry.
I especially like the advice to drink before you’re thirsty because if you wait until you’re thirsty, it’s too late. How would we have survived as a species if our thirst mechanism didn’t work?
Dan Goldberger says
For an article with footnotes to scientific journals, refer to Am Fam Physician.2019;99(8):482-99 for a good review of heat related illness. The authors agree that the neuromuscular control theory of cramps has gained favor over the dehydration/electrolyte theory. They also comment that the causes of cramps are likely multi-factorial and fluid/electrolyte replacement can play a role in some cases. Great advice Coach!
Greg Titus says
That was one excellent article. Thanks!