This article was originally published during the depths of the big European heat wave in 2003 that was indirectly linked to over 30,000 (not a typo) deaths. That was also the Tour where Lance got completely dehydrated and lost the first big TT to Ullrich. We’re reprinting it here with some give and take between practical advice from Josh Horowitz of Liquid Fitness and my scientific feedback.
The “Dry” Facts…
Camelbak’s got the most scientifically accurate slogan in all of corporate history when it came up with the “Hydrate or Die” motif. The proper mix of carbohydrates, proteins, fats, vitamins, and minerals in your diet is important, but water trumps them all as THE essential nutrient. IRA hunger strikers in the late 1970’s lasted 60-80 days without food. However, if they had tried that without drinking water, they probably wouldn’t have lasted a week! And that’s just lying about shouting anti-English slogans. Add exercise and the heat of summer and the threat of dehydration becomes even more severe. The world record sweat-meister? Try 3.7 kg/h by the runner Alberto Salazar (1) during training prior to the 1984 Olympics in LA. That’s over 5% of his body weight every hour!
Make no mistake about it, short of sickness or injury, NOTHING will affect your daily performance more than your hydration status. Study after study has demonstrated that even a very slight amount of fluid loss (1% body weight) results in significantly decreased performance in both endurance and power sports. In fact, my own Ph.D. research (2) found that proper hydration prior to exercise (i.e., making sure you’re not dehydrated to begin with) is more important than either fitness or heat acclimation in determining your tolerance to exercise in the heat.
What’s so bad about dehydration? The first place that fluid is lost from is your blood. With less blood to pump throughout your body, your heart has to pump more frequently to maintain the same rate of blood delivery to the muscles. This results in “cardiovascular drift,” where your heart rate increases even though your power output is constant, placing unnecessary stress on your heart. In addition, the body also tries to preserve blood flow to the muscles, meaning there is less blood going to the skin to dissipate heat. Keep this going much more and the elevated body temperature will ultimately cause fatigue by actually decreasing the ability of your brain to activate your muscles (3). When dehydration gets even worse, then the water loss from your muscles themselves will cause cramps, spasms, or worse. You’ve all seen the images of Paula Newby-Fraser staggering and collapsing within sight of the Hawaiian Ironman finish line, so take steps to make sure nothing like that ever happens to you.
Planning to Drink
It is absolutely critical to plan out and practise your hydration strategy. Here are some practical tips from Josh and my scientific comments on them:
Josh: If you have a big event the next day, drink a big bottle the night before. When my team is at a hot stage race such as the Tour of the Gila, we go by the rule, if you don’t wake up 2 or 3 times during the night to pee, you probably haven’t drunk enough. Make sure your pee is clear the night before and the morning of. Unless you are taking a ton of vitamin supplements, clear pee means you are well hydrated.
Stephen: Due to changes in fluid distribution throughout your body, both body mass itself and urine colour can be inaccurate measures of actual hydration status. For example, if you are in a state of lowered hydration status (hypohydration), drinking lots of water will still produce fairly clear urine. Therefore, body mass and urine colour can be useful indices for long-term monitoring, but may not be able to pick up problems with acute changes in hydration. The most accurate and reliable indices of fluid balance remains blood measures, which are not overly practical for athletes. This again highlights the need to maintain a long-term and consistent hydration plans and not “cram” the fluid intake or recovery.
Josh: If you have a problem remembering to drink on the bike, make a rule for yourself. No matter how you feel, every 5 minutes take a sip, set your watch alarm every 10-15 min to remind yourself to drink, or better yet, take a sip any time you see anyone else in the group do it.
Stephen: The average athlete can easily lose over 1 kg of sweat every hour, and cyclists can easily exceed this to the tune of 1.5-2 kg in hot weather. That is because one of the primary adaptations to both aerobic training and heat acclimatization is an increased sweating response. It is critical that you train yourself to replace as much of the fluid loss as possible DURING the workout.
This point also raises the recently popular concept of hyponatremia or water intoxication. This is a condition where you can drink so much water that you end up diluting your body fluids and electrolyte concentration in the blood. This can be just as dangerous, if not more so, than dehydration. I will cover this in much more detail in my next Toolbox. But for now, for prolonged exercise, avoid drinking solely water and mix in some sports drink. In addition, drink sensibly but don’t go overboard. Remember that your body can only empty and absorb about 1L/h from your gut, so don’t get into chugging contests while exercising.
Josh: Drink your favorite hydration drink and don’t add anything to it. The reason I say favourite is because if you like the taste, you’ll drink more. The reason I say don’t add anything to it (or consume electrolyte pills) is that the hydration drink already has the proper balance of electrolytes. If you supplement with more, your cells are just going to need more water to keep an optimum balance.
Stephen: Just as the best bike in the world is worthless if it doesn’t fit you correctly, the scientifically ideal sports drink is junk if you don’t like the taste of it and therefore won’t drink enough of it. For example, some important research has been done to test the effects of different flavours on voluntary drinking rates in children. Within reason, all of the major sports drinks out there fall within the generally accepted consensus on ideal carbohydrate and electrolyte composition, so experiment to find out what you find most drinkable. There is a major debate ongoing concerning whether scientists should be advocating
Josh: During stage races or multi day events, weigh yourself before and after each ride to see how much water weight you have lost. If you have lost more than 3% water weight then you have seriously harmed your muscle’s ability to perform and you know to drink more next time.
Stephen:Over the course of a stage race or a hard training block, proper hydration becomes even more important. Pack your own water and drink powder with you to races so that you don’t have to rely on others. Research by my former boss Ron Maughan (4) shows that you need to drink at least 150% and preferably 200% of your fluid loss post-exercise to ensure that you return to your normal hydration levels. In addition, the drink should have at least moderate amounts of sodium to help keep the fluid in your body. Carbohydrates are not essential for hydration purposes as long as you’re eating adequately, but it won’t hurt to have some to improve taste.
Josh: Warm up is a place where I think people forget to drink. When it is extremely hot, cut your warm up time by 40%. Your muscles will already be warm and if you do more than about 35 minutes, you’re going to be cooked. If you don’t have to get off your trainer during warm up at least once to pee, you aren’t drinking enough.
Stephen:This advice is especially important in crits and time trials, where the races are relatively short. Drinking DURING these events are mainly psychological, because there is not enough time for the fluid to be emptied from your stomach and absorbed through the intestines to do much good. My doctoral research demonstrated that maintaining normal hydration status prior to exercise was more beneficial than drinking during exercise of 90 min or less in very hot environments. However, some research has demonstrated that drinking a carbohydrate drink during a 1 h time trial improved performance (distance covered) compared to water alone, theorizing that the carbohydrate may trip a feedback loop directly to the central nervous system and enabling higher power outputs.
Check out the Gatorade Sport Science Institute for posibbly the best site on hydration and sport nutrition on the web!
1. Armstrong LE, Hubbard RW, Jones BH, and Daniels JT. Preparing Alberto Salazar for the heat of the 1984 Olympic marathon. Physician and Sportsmedicine 14: 73-81, 1986.
2. Cheung SS, McLellan TM, and Tenaglia S. The thermophysiology of uncompensable heat stress. Physiological manipulations and individual characteristics. Sports Med. 29: 329-59, 2000.
3. Nybo L, and Nielsen B. Hyperthermia and central fatigue during prolonged exercise in humans. J. Appl. Physiol. 91: 1055-60., 2001.
4. Shirreffs SM, Taylor AJ, Leiper JB, and Maughan RJ. Post-exercise rehydration in man: effects of volume consumed and drink sodium content. Med. Sci. Sports Exerc. 28: 1260-1271, 1996.
Stephen Cheung is an Canada Research Chair in the Department of Physical Education & Kinesiology at Brock University in St. Catharines, Ontario, with a research specialization in the effects of thermal stress on human physiology and performance. He can be reached for comments at firstname.lastname@example.org.