In January 2009, Haile Gebrselassie won the Dubai Marathon in 2 hours, 5 minutes and 29 seconds. When he was measured afterwards, he had lost 9.8% of his body weight.
By the rule athletes are taught, that should have been impossible. Lose 2% of your body weight in sweat, the rule says, and your athletic performance starts to fall apart. Gebrselassie lost almost five times that, and won. Nobody had told him.
The rule came from the lab, where people often ride or run at a set pace until they stop. Races are not run that way, and when it comes to hydration, the people who win them seem to know something the advice does not.
What the fastest runners actually do
When ten elite men were followed through 13 major city marathons, nine of them winners, their drinking was timed. Over a whole marathon, they spent about 25 seconds drinking. The shortest total was under two seconds. The longest was under a minute. Less time than it takes to read this paragraph.
That came to about half a litre an hour. Their estimated weight loss over the race was between 6.6% and 11.7%. These were the best marathon runners in the world, winning, while breaking the 2% rule several times over.
It is not only the elite. At the 2009 Mont Saint-Michel Marathon in France, 643 finishers were weighed before and after the race. Those who finished in under three hours had lost about 3.1% of their body weight. Those who took three to four hours had lost 2.5%. Those who took more than four hours had lost 1.8%. The faster the runner, the more weight lost.
That makes sense once you think about it. Faster runners work harder, sweat more and stop less. The weight they lose is the cost of speed, not the cause of slowness.
And not all of that weight is water you need back. Why Processed Food Is Hard to Leave — and When It Gets Easier has why: the body stores carbohydrate with three to four parts water, and as the store is burned, that water goes. Burning fuel makes water as well. Think You’re Hydrated?, linked below, has the fat that yields more water than it weighed. Part of what a marathoner loses on the scale is fuel burned and the water that came with it.
Training changes the plumbing as well. Endurance training expands the volume of your blood, and in the first two to four weeks almost all of that rise is plasma, the watery part. After that, the increase spreads between plasma and red cells. A trained body carries more water in its blood before it has drunk a drop.
Drink to thirst
If 2% does not wreck performance in a race, how should an athlete drink?
The answer that holds up is the simplest one. When tests of cyclists racing the clock over a set distance were pooled, losing about 2.2% of body weight made no measurable difference to performance compared with staying topped up. Drinking to thirst beat drinking less than thirst asked for, and it did no worse than drinking more.
Thirst is a better guide than it gets credit for. Think You’re Hydrated? Why Your Body Might Be Thirsty for More has how thirst runs ahead of the blood, reading signals from your mouth and throat and switching off before the water has even arrived. It is a fast, well-made system. Most of the time, it does not need a schedule. It certainly does not need an app.
Thirst softens with age, though. 7 Fun and Tasty Ways to Stay Hydrated Without the Boredom, linked below, has the older men who, after a day without water, were less thirsty than younger men and drank less, though their blood showed they needed it more. For an older athlete, thirst is a gentler alarm, and pale yellow urine is the better check.
Where "drink ahead of thirst" came from
The sports drink has a birthday. In 1965, a team at the University of Florida led by Robert Cade mixed a drink for the university's football team, the Gators, to replace the carbohydrate they burned and the water and electrolytes they lost in sweat. They called it Gatorade.
The drinking advice grew bolder from there. The American College of Sports Medicine went as far as recommending that athletes drink "as much as tolerable". Tolerance turned out to be the problem.
The drink itself is less impressive than the marketing. What to Drink Instead of Plain Water — and What the Popular Alternatives Do to Your Body has the 13-drink test where a sports drink kept no more water in the body than plain water. Heat Survival Guide, linked below, puts it plainly: the branded sports drink is mostly water with sugar. It is acidic as well. The Hidden Cost of Your Daily Sugary Drink has the 379 drinks from American shelves where sports drinks came close behind cola for dissolving tooth enamel, sugar-free or not.
And the push to drink more had a price. 7 Fun and Tasty Ways to Stay Hydrated Without the Boredom has the 2002 Boston Marathon, where 13% of the runners tested at the finish had too little sodium in their blood. The ones most at risk had gained weight during the race. They had drunk more than they sweated, which the elite runners above did not.
Low blood sodium is easy to mistake for dehydration. In its early stages it can bring nausea, vomiting, headache, bloating, and swelling of the hands, legs and feet. If those come after drinking plenty, more plain water is the wrong answer.
By 2015, eight deaths from low blood sodium during exercise had been documented since 1985, and an international consensus conference on the condition concluded that drinking to thirst is enough to prevent both dehydration and that dangerous dilution. Thirst had been a good enough guide all along.
Salt and sweat
Sweat is not water. It carries salt out of you, and on a long, hot, sweaty session that adds up.
This is where water alone falls short. Why "Drink More Water" Is Incomplete Advice, linked below, has why salt is the other half of hydration, and why it should be good salt. On the long days, a pinch of good salt, such as , in your water, a salted meal, or a mug of salted bone broth puts back what the sweat took. Sweat is a salt bill. Pay it at dinner. When there is no time to make broth, stir into hot water. On short sessions in cool weather, you are unlikely to need anything but water and your next meal.
Read your own sweat
No two people sweat the same. When the methods and findings were reviewed, both how fast people sweat and how salty that sweat is varied a great deal from person to person, and within the same person from one day to the next. Heat, effort and fitness all change it.
So learn your own. The simplest accurate measure is the scale. Any reliable bathroom scale will do, such as this . Weigh yourself before a session and again after it, in the same clothes, and allow for what you drank. The difference is what you sweated. Do it on a few different days, hot and cool, easy and hard, and you will know your own body better than any chart can tell you.
Your clothes keep records too. If your dark training top dries with white marks, or you finish with grit at your hairline and salt on your skin, you are probably a salty sweater. Your T-shirt has been telling you for years. You lose more salt than the person next to you, and your long days need more of it back.
And check before you start. Pale yellow urine before a session means you are starting from a good place. Dark yellow means drink first.
Heat
The body learns the heat, and it learns fast. Faster than you learn to pack a hat.
With repeated time in the heat, you start sweating sooner and more freely, more blood goes to your skin, your core temperature runs lower, your heart works less hard at the same effort, and you hold on to fluid better. Heat Survival Guide, linked below, has the tests of short heat training where a week or less of exposures was already enough to improve how people performed.
Cold drinks help in the moment too. When ten men in 34°C heat drank either ice slurry or the same amount of cold water before running to exhaustion, the slurry dropped their core temperature further, they felt cooler, and they ran for about 50 minutes against about 41.
So if a race is going to be hot, do some training in the heat before it. The first warm sessions are the hardest, and the ones where salt and water matter most.
Cramps
Cramps are usually blamed on water or salt. The evidence is less tidy.
The Quiet Signals of Mineral Deficiency has the 210 Ironman triathletes where the 43 who cramped had the same blood salts and the same fluid loss as everyone else. What marked them out was racing faster. Fatigue in a hard-working muscle seems to matter more than what is in the bottle.
Salt still has a trick, though, and it works through the mouth. Why "Drink More Water" Is Incomplete Advice, linked below, has the sip of pickle juice that cut a cramp short by almost fifty seconds, too fast for the salt to have reached the blood.
After training
Drink to thirst after training too. Your body will tell you when it has caught up, and pale yellow urine later in the day confirms it.
What you drink matters more than how fast. What to Drink Instead of Plain Water, linked above, has why salted bone broth stays in the body better than water alone, and the 13-drink test where full-fat and skimmed milk kept more fluid on board than water did, if milk suits you.
Food does a lot of the work too. When eight people who had sweated off about 2% of their body weight in warm, humid conditions drank the same amount either as a commercial sports drink or as water with a meal, the meal left them passing less urine afterwards. More of the water stayed. A salted meal is a rehydration drink with a knife and fork.
Go easy on the celebration, though. After exercise in the heat, drinks with up to 2% alcohol rehydrated people about as well as alcohol-free ones, but a 4% drink, the strength of an ordinary beer, slowed the recovery of their blood and plasma volume. Water, broth or a meal first. The beer can wait.
Make it a proper meal. Beef, salmon and chicken bring the protein your muscles need to repair and the potassium your sweat took, with salt on the plate doing the rest.
Back to Dubai
Gebrselassie did not win in Dubai by drinking to a plan. He ran as hard as he could, drank a little along the way, and finished nearly a tenth lighter. His body knew what it needed better than the rule did. Rules are written for averages. Bodies are not averages.
You are probably not running a marathon in just over two hours. But the same body is in you: a thirst that runs ahead, kidneys that keep what they can, and sweat that tells you what it took.
Next time you train for over an hour, weigh yourself before and after, and drink to thirst in between.
Still cramping and flat despite drinking all day? Why "Drink More Water" Is Incomplete Advice — what salt does in every cell, where the salt fear came from, and why it should be good salt.
Training or racing in the heat? Heat Survival Guide: How to Stay Cool and Safe in Hot Weather — why sweat only works if it can leave, the week it takes your body to learn the heat, and the signs that heat exhaustion has turned into heatstroke.
Know a runner who forces down a bottle every few miles? Send them this, and the 25 seconds.
Disclaimer: This article is general information. For advice about your own health, talk to a qualified health professional. If you have heart or kidney disease, or take medicine that affects your fluid or salt, check before changing how much you drink or salt. Confusion, collapse or hot, dry skin during exercise in the heat is an emergency: call your local emergency number.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
Sources
Wikipedia. Dubai Marathon. en.wikipedia.org
Beis LY, Wright-Whyte M, Fudge B, Noakes T, Pitsiladis YP (2012). Drinking Behaviors of Elite Male Runners During Marathon Competition. Clinical Journal of Sport Medicine 22(3):254–261. doi.org/10.1097/JSM.0b013e31824a55d7
Zouhal H, Groussard C, Minter G, et al. (2011). Inverse relationship between percentage body weight change and finishing time in 643 forty-two-kilometre marathon runners. British Journal of Sports Medicine 45(14):1101–1105. doi.org/10.1136/bjsm.2010.074641
Kreitzman SN, Coxon AY, Szaz KF (1992). Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. The American Journal of Clinical Nutrition 56(1):292S–293S. doi.org/10.1093/ajcn/56.1.292S
Wikipedia. Metabolic water. en.wikipedia.org
Convertino VA (1991). Blood volume: its adaptation to endurance training. Medicine & Science in Sports & Exercise 23(12):1338–1348. doi.org/10.1249/00005768-199112000-00004
Goulet EDB (2011). Effect of exercise-induced dehydration on time-trial exercise performance: a meta-analysis. British Journal of Sports Medicine 45(14):1149–1156. doi.org/10.1136/bjsm.2010.077966
Zimmerman CA, Lin YC, Leib DE, et al. (2016). Thirst neurons anticipate the homeostatic consequences of eating and drinking. Nature 537(7622):680–684. doi.org/10.1038/nature18950
Phillips PA, Rolls BJ, Ledingham JGG, et al. (1984). Reduced Thirst after Water Deprivation in Healthy Elderly Men. New England Journal of Medicine 311(12):753–759. doi.org/10.1056/NEJM198409203111202
Wikipedia. Gatorade. en.wikipedia.org
Wikipedia. Exercise-associated hyponatremia. en.wikipedia.org
Maughan RJ, Watson P, Cordery PA, et al. (2016). A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. The American Journal of Clinical Nutrition 103(3):717–723. doi.org/10.3945/ajcn.115.114769
Reddy A, Norris DF, Momeni SS, Waldo B, Ruby JD (2016). The pH of beverages in the United States. Journal of the American Dental Association 147(4):255–263. doi.org/10.1016/j.adaj.2015.10.019
Almond CSD, Shin AY, Fortescue EB, et al. (2005). Hyponatremia among Runners in the Boston Marathon. New England Journal of Medicine 352(15):1550–1556. doi.org/10.1056/NEJMoa043901
Hew-Butler T, Rosner MH, Fowkes-Godek S, et al. (2015). Statement of the Third International Exercise-Associated Hyponatremia Consensus Development Conference, Carlsbad, California, 2015. Clinical Journal of Sport Medicine 25(4):303–320. doi.org/10.1097/JSM.0000000000000221
Baker LB (2017). Sweating Rate and Sweat Sodium Concentration in Athletes: A Review of Methodology and Intra/Interindividual Variability. Sports Medicine 47(S1):111–128. doi.org/10.1007/s40279-017-0691-5
Périard JD, Racinais S, Sawka MN (2015). Adaptations and mechanisms of human heat acclimation: Applications for competitive athletes and sports. Scandinavian Journal of Medicine & Science in Sports 25(S1):20–38. doi.org/10.1111/sms.12408
Chalmers S, Esterman A, Eston R, Bowering KJ, Norton K (2014). Short-Term Heat Acclimation Training Improves Physical Performance: A Systematic Review, and Exploration of Physiological Adaptations and Application for Team Sports. Sports Medicine 44(7):971–988. doi.org/10.1007/s40279-014-0178-6
Siegel R, Maté J, Brearley MB, et al. (2010). Ice Slurry Ingestion Increases Core Temperature Capacity and Running Time in the Heat. Medicine & Science in Sports & Exercise 42(4):717–725. doi.org/10.1249/MSS.0b013e3181bf257a
Schwellnus MP, Drew N, Collins M (2011). Increased running speed and previous cramps rather than dehydration or serum sodium changes predict exercise-associated muscle cramping: a prospective cohort study in 210 Ironman triathletes. British Journal of Sports Medicine 45(8):650–656. doi.org/10.1136/bjsm.2010.078535
Miller KC, Mack GW, Knight KL, et al. (2010). Reflex Inhibition of Electrically Induced Muscle Cramps in Hypohydrated Humans. Medicine & Science in Sports & Exercise 42(5):953–961. doi.org/10.1249/MSS.0b013e3181c0647e
Maughan RJ, Leiper JB, Shirreffs SM (1996). Restoration of fluid balance after exercise-induced dehydration: effects of food and fluid intake. European Journal of Applied Physiology and Occupational Physiology 73(3-4):317–325. doi.org/10.1007/BF02425493
Shirreffs SM, Maughan RJ (1997). Restoration of fluid balance after exercise-induced dehydration: effects of alcohol consumption. Journal of Applied Physiology 83(4):1152–1158. doi.org/10.1152/jappl.1997.83.4.1152