Cycle racing and endurance rides can lose you 1.6 liters per hour in sweat and respiration, rising to 6 liters in very hot conditions. Unless you drink enough to replenish the loss, dehydration may soon set in, causing an imbalance in your body chemistry and putting extra strain on your heart. Cyclists, coaches and medical advisers agree that dehydration can affect both performance and health. However, there is some debate over how much it matters and what to do about it.
Basic Advice
For many years, the American College of Sports Medicine (ACSM) has warned athletes about the threat of dehydration, which impairs body temperature control mechanisms and blood circulation. Losing over 4 percent of body weight in fluid may also affect your performance by up to 10 percent. ACSM experts recommend that before, during and after your ride you drink as much water as you lose in sweat.
However, disproportionate amounts of plain water may upset the sodium and electrolyte balance of your blood. This can lead to dilutional hyponatremia, or sodium deficiency, which can cause cramps, fatigue and confusion. So if you are cycling far or fast -- over two hours, for example -- consider using special sports drinks, which replenish electrolyte as well as liquid levels.
How Much to Drink
As a basic guide to your sweating rate, weigh yourself before and after an hour's ride in hot weather. You can then work out how much sweat you are likely to lose on a longer ride and, therefore, how many water bottles you need to carry on the bike to replenish what you lose. ACSM coaches typically recommend drinking 5 to 11 oz. every 15 minutes while training. The exact amount depends on heat, humidity and altitude; how strenuously you work; and whether you have taken diuretics like alcohol.
Alternative Views
Some cyclists perform very well without drinking much. They argue that dehydration may offer advantages, such as a lighter body that takes less effort to propel along a track at speed. Also, you may be able to keep up a faster average speed by not slowing down for a drink at aid stations.
People clearly vary in how much extra fluid they need and how efficiently they perform without it. Always pay attention to your own body's warning signs, such as headache, thirst or fatigue, and remedy them before they lead to exhaustion or heat-stroke.
Tips on Hydration
Drink a little at a time, starting before you are thirsty and ideally about two hours before riding. Thirst can be a late and inconsistent warning of dehydration.
Carbohydrates in sports drinks can help keep you going. Choose brands you find palatable, so you can drink enough without feeling sick. Add a pinch of salt to avoid sodium deficiency. You can save money by mixing your own energy drinks. Look out for signs of dehydration in yourself and other riders. Nausea, headache, cramps, dizziness or confusion mean you need to stop at once to rehydrate.
References
- American College of Sports Medicine: ACSM Clarifies Indicators for Fluid Replacement
- Cycling Research News: Is Dehydration Over-rated?
- "International Journal of Sports Medicine"; Impaired High-Intensity Cycling Performance Time at Low Levels of Dehydration; R. M. Walsh, et al.; 1994
- AthletiCamps; Fueling for Optimum Sports Performance; Marlia Brand; 2011
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