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  Last updated: 6/18/2010


Although water is not a source of Calories to power your activities, adequate fluid intake and hydration are at least as important as Calorie replacement to maximize one's athletic performance. The single biggest error of many competitive athletes is a failure to replace fluid losses during training and competitive events. This is especially true in cycling where evaporative losses are significant and can often go unnoticed even though fluid loss with sweating and loss through the lungs can easily exceed 2 quarts per hour. (Respiratory fluid losses are not insignificant. Up to 60% of overall fluid loss can be via the lungs - which means that even swimmers can get dehydrated.)

To maximize your performance, it is essential that fluid replacement begin early and continue throughout a ride. A South African study comparing two groups of cyclists (one focusing on staying hydrated, the other not) exercising at 90% of their personal maximums demonstrated a measurable difference in physical performance as early as 15 minutes into the ride.

Fluid losses during exercise decrease the circulating blood volume as well as the water content of individual muscle cells. The impact on performance is directly related to the level of dehydration. Early dehydration is defined as a >1% loss of body weight as a result of fluid loss. Unreplaced water losses equal to 2% of body weight (about 3 pounds for the average rider) will impact heat regulation, at 3% there is a measurable decrease in muscle cell contraction times, and when fluid losses reach 4% of body weight, there is a 5 to 10% drop in overall performance (which can persist for up to 4 hours after rehydration takes place). Thus it is essential to anticipate and regularly replace fluid losses. Thirst is not a reliable indicator of your state of dehydration as it is often not triggered until one has lost 0.8 - 2% (of body weight). Maintaining plasma volume is an important piece of an overall strategy to optimize your physical performance.

How much water do you need to maintain a normal state of hydration without a daily exercise)? For a 70 kilogram adult, about 2500 to 3000 cc per day. This equates to about 4% of your body weight If your diet is well balanced, approximately 1000 cc (4 cups) is water in fruits, vegetables, and other foods you eat. Another 1 cup is produced when your body metabolizes carbohydrates, and the balance - about 7 cups - needs to be fluids you drink.

If you then exercise for an hour or two, add in replacement for the losses from sweat and respiration. Under normal environmental circumstances, you will lose 1 - 2 liters of sweat per hour, and if the ambient temperature is high, this can be as high as 4 - 6 liters per hour.

What are other factors, besides exercise, that can influence your fluid needs (and exacerbate dehydration)?

Under normal conditions, while riding you should be taking in a minimum of 4 to 5 ounces of fluid every 15 minutes or 1 to 2 standard water bottles per hour. When extreme conditions of heat and humidity are anticipated, and the risks of dehydration are higher, the following strategy of maximizing hydration before you start the activity can be a good preventative measure.

If you want a simple measure of the effectiveness of your personal hydration program, weigh yourself before and after a long rides (without clothes to avoid inaccurate weights from sweat soaked clothing). A pound of weight lost equals 16 ounces (1 pint or 2 cups) of fluid; a quart (4 cups) is 2 pounds. For the purposes of calculating your replacement needs, a standard water bottle (20 ounces) weighs about 1 1/4 pounds. With this information, you can tailor YOUR OWN fluid replacement program.

For those who practice the philosophy of "if a little is good, a lot is better", it should be mentioned that there are risks associated with over correcting fluid losses of exercise. There have been reports of hyponatremia (low blood sodium concentration) resulting in seizures in marathon runners who over replaced sweat losses (which contain both salt and water) with water alone. This is rarely a problem for cycling events less than several hours in duration (except under extreme environmental conditions of heat or humidity) and becomes a potential problem only for events lasting more than 5 hours.


Q. Do electrolyte drinks (those containing minerals such as sodium and potassium) provide an advantage over pure water alone?

A. Not for rides of 1 to 2 hours. When two groups exercised for 2 hours at 67% VO2 max (with average fluid losses of 2300 ml) there was no advantage to rehydrating with electrolyte drinks versus water alone. For longer rides, especially over 5 hours in duration (100 miles) or in conditions of extreme heat and humidity, using electrolyte containing drinks for sodium replacement will decrease the risk of dilutional hyponatremia. With the large volumes needed for rehydration in long events, palatability and digestive tract tolerance are important in the selection of a replacement fluid.

In extreme conditions you might consider adding a pinch of salt to each water bottle of electrolyte replacement drink. For example, Gatorade doesn't contain much sodium. This added salt will help to prevent hyponatremia. In the same way, salting your food liberally the day before a hot-weather ride may help and there are personal stories that this prevents cramps in some individuals. A word of caution, if you are on a sodium restricted diet, check with your physician to make sure that adding salt won't be a health hazard for you.

Additional thoughts on drinks for those longer rides (and keeping hydrated):


In summary, drinking 1 to 2 quarts per hour of plain water is adequate for rides of 1 1/2 to 2 hours. For longer rides, where the body's glycogen stores will be depleted, carbohydrate containing fluids take on increased importance (glucose containing liquids can deliver Calories from the mouth to the muscles in as little as 10 minutes as compared to solid foods and energy bars which empty more slowly from the stomach). In most individuals, an 8 to 10 % concentration is the optimal. Glucose polymers provide the ability to increase total Calories per quart without risking the side effect of an unpalatable, sweet taste. Aside from palatability, there is no proven advantage of polymer containing drinks over simple sugar (glucose) drinks. Although there are many commercial drinks available, the old standbys of apple juice and cola drinks are probably the least expensive per Calorie provided. In the pre and post ride period, the high Calorie, easily absorbed, glucose polymer sports drinks offer an advantage for taking in large amounts of carbohydrate in the sweet spot of 30 - 60 minutes post ride aiding rapid rebuilding (or restocking) glycogen stores. For those of you interested in saving a few $$, take a look at this site for some ideas on homemade energy drinks.

For longer rides, don't forget the risks of overdoing rehydration with pure carbohydrate (electrolyte free) drinks alone. If you plan to ride more than two or three hours, it's worth considering a commercial electrolyte containing drink, and if you are going to be riding 5 hours or more, it is essential to pace your fluid replacement rate (and keep an eye on your weight during training rides to be certain you are not overcompensating).


Commercial sports drinks are the easiest, but are pricey. Often times complex carbohydrates can be purchased in a health food store and mixed at home with a flavor of your choice or used to supplement a current favorite drink.

Maltodextrin is a corn starch molecule which has been broken down into glucose polymers (chains of glucose molecules). When added to water or other drinks, it increases the energy content without the disadvantage of an overly sweet taste and a highly concentrated solution which may delay gastric emptying. It may be useful as a post ride supplement, but does not provide any advantages to breads, cereals, grains, etc. as a regular daily energy source. Directions are usually available from the container, but can vary from 1/2 cup in 8 pounces to 3/4 cup in 32 ounces. You may need to experiment to find the best concentration for your personal physiology.

A 16 ounce water bottle (480 cc) of a 7% sugar solution at 4 Cal per gram of carbohydrate will contain about 136 Calories. If you add 1/2 cup of Carboplex (a commercial maltodextrin) you will add another 220 Calories almost tripling the energy density (concentration) of your drink with minimal chances of nausea or other side effects.

A word of warning about overdoing it with sports drinks. The American Academy of Pediatrics has released a position paper on sports and energy drinks pointing out the risks of over stimulation (for caffeine containing drinks) and obesity when they are used without the exercise to use the extra Calories consumed. This is especially a hazard for adolescents and preteens.



There have been some encouraging studies on the use of glycerol to minimize the negative impact of dehydration on performance. For those interested in a commercial product, try the internutria website.

Except under extreme conditions, electrolytes (particularly sodium chloride or salt) do not need to be replaced along with fluids.


Q. I currently average about 225 to 250 miles a week with a metric century or a full century on the weekends (and 1 or 2 rest days and recovery ride during the week). I have been weighing myself before rides and after and its a little alarming, on average I lose about 4-6 pounds on every ride I take! I just completed a 70 mile with 3 big climbs, in 4:00:59, when I started I weighed 148 lbs when I finished I weighed 142 lbs! I Drank 4 24 ounce water bottles with Gatorade Endurance formula, had two Gels and a cliff bar (oh yeah and had a cliff bar to start for Breakfast at 6am). I drank so much I feel a little gassy toward the end and did not feel better until i burped many times. Is this weight loss normal for a rider my size? Our average temperature in Phoenix when I ride is 92-95, with a little humidity in July-Aug (30-50%); should I be alarmed? Do I need to rethink my whole hydration plan for the whole ride? - C.H.

A. When you lose weight on a ride, you can assume it is water weight - so you were 6 pounds or a quart and a half behind in fluids (a quart or 4 cups = 2 pounds)at the end of the ride. (In ounces, that is 16 x 6 or 96 ounces.) That is 4% of your body weight - which will impact your performance. The bottom line - you do need to rethink your hydration plan.

Over the four hours, you drank 96 ounces or 24 ounces per hour. I think that is about the maximum you can take in per hour (and empty from your stomach). But you may get some additional benefit by drinking 20 oz of cool water 2 hours before exercise and another 8 to 16 ounces 30 minutes before exercise to assure that you are fully hydrated when you start. You might consider trying other sports drinks as sometimes one will agree with your physiology better than another and thus empty a bit more quickly from your stomach. Other strategies would include proper clothing (white to reflect the heat), and I'd also think about switching to a completely liquid diet for the few hours before and during the ride - even the cliff bar may be enough to lengthen gastric emptying time and contribute to the bloated feeling.

Q.Do you know of any recipes for sugar free sports drinks?? My daughter is rotting her teeth, partly because of the dehydration from running, and partly because of sports drinks.? We'd like to mix up something ourselves. - T.

A. Sports drinks provide four things:

  1. Water (this could come right from the tap as well.
  2. More palatable (so one does adequately rehydrate) - any flavoring would do
  3. electrolytes (salt being the most common, then perhaps potassium). But unless she is running 5 hour marathons, probably not a big deal.
  4. carbohydrate - to replace what is being metabolized and which is what works to promote tooth decay. A complex carb might be less of a problem (Carboplex) but anything with simple glucose or sucrose is going to be a problem with a sugar film on the teeth to aid the bacteria which cause decay.
Any flavored water (may are commercially available) would work to provide the fluid and a better taste than just water alone. But if she is exercising more than 2 hours she will start to run out of carbs. How long does she run?? Does she brush immediately afterwards (which might help a bit to eliminate the sugar rich coating on her teeth).

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