Hydrate or Die!
You’re probably used to carrying a water bottle around with you everywhere you go and drinking so much that you run to the bathroom more often than my almost three-year old son. Meanwhile, sport drink companies sprout faster than tech companies, each touting itself as the magical elixir. So just how much do you need to drink and what should you be chugging? Grab your bottle and fill up on this two-part series on the latest science behind hydration…
The “Dry” Facts…
Camelbak’s got the most scientifically accurate slogan in all of corporate history. 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 calling the English tossers. 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.
Planning to Drink
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. It is absolutely critical to plan out and practise your hydration strategy. Here are some things to consider:
• The average cyclist can easily lose over 1 kg of sweat every hour, and it is critical that you train yourself to replace as much of the fluid loss as possible DURING the workout. How do you figure out how much fluid you need? Take your weight before and after training and a record of how many bottles you drank to estimate your typical sweating rate. Set your watch alarm every 10-15 min to remind yourself to drink.
• 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.
In my next article in two weeks, I will discuss the ideal drink composition in terms of whether water alone is sufficient, and what type and concentration of carbohydrates and minerals might be helpful. In the meantime, check out the Gatorade Sport Science Institute for 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 Associate Professor of Kinesiology at Dalhousie University in Halifax, Nova Scotia, Canada, with a research specialty in the effects of thermal stress on human physiology and performance. He has been an avid roadie since beginning university in the mid-eighties, and still has non-indexed downtube shifters on his winter bike and wool jerseys hanging in his closet. He can be reached for advice or comments at [email protected]