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  Latest update:9/17/2022


Adequate fluid intake and hydration are at least as important as Calorie replacement to maximizing athletic performance. Fluid losses during exercise lead to a decrease in the circulating blood volume as well as the water content of individual muscle cells.

Maintaining an adequate plasma volume is a key piece of an overall strategy to optimize physical performance. Failing to replace fluid losses is a common error of many competitive athletes both while training and in competitive events, and is especially common in cycling where significant evaporative losses can often go unnoticed even as fluid loss from sweating and expired air (up to 60% of total losses) can easily exceed 2 quarts per hour.

And it can happen quite quickly. A South African study comparing two groups of cyclists (one focusing on staying hydrated, the other not) exercising at 90% of their personal VO2max, demonstrated a measurable difference in performance as early as 15 minutes into the ride emphasizing the importance of anticipating and regularly replacing fluid losses.

The decrement in performance is directly related to the degree of dehydration.

Thirst is not a reliable indicator of the level of dehydration as it is often is not triggered until one has lost 0.8 - 2% (of body weight).

Hydration and Performance - is total volume replacement necessary?

This article highlights how conclusions as to optimal hydration have changed over the last 50 years. Work from the 1960s through the late 1980s touted complete fluid replacement as the goal for maximize endurance performance. This philosophy was codified in 1996 in the American College of Sports Medicine (ACSM) fluid replacement Position Stand which urged the full replacement of sweat loss during exercise.

Then things began to shift. Based on additional studies and observations of real life performance, the ACSM revised its recommendations on fluid replacement in 2007 proposing a goal of 400-800 mL/h, varying depending on the athlete's size, environmental conditions, and exercise intensity. It shifted the goal from maintaining complete rehydration to limiting fluid loss to less than 2% of body weight.

About the same time the theory of a central governor was being proposed. This theory proposed the idea of an area in the brain (the central governor) that integrated multiple sensory inputs and then modified exercise (limiting it in certain cases such as overheating) by limiting the neural signals to muscle cells. In that way it protected the athlete from the harm of excesses in endurance and sprint activities. This theory suggested that it was the sensation of thirst, rather than the absolute level of dehydration that was the critical factor leading to a decrement in performance.

So we had a move to acceptance of "thirst" as the most reliable indicator of personal fluid needs (much akin to using perceived exertion as a measure of exercise limits in training). But the pendulum continues to swing, and a few studies have questioned even that approach to fluid replacement - the focus on thirst as a better measure of an indicator of dehydration (and limited performance) than using weight loss or total % BW dehydration.

The details below are based on this article as well as comments excerpted from an additional article by the lead author.

Although this result is intriguing, it is just a single study and as such will need confirmation before we can take the conclusions to the bank. Here are 3 examples that indicate to me things are still not crystal clear: So what do I conclude? What am I going to do? Although this article suggests some latitude in fluid replacement, and gives an easy out to those of us who are not good at fluid replacement, common sense says that the more you stay in physiologic balance (homeostasis) and replace fluid (as well as glycogen) losses during and after a ride, the more competitive you (and I) will be in endurance events.


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):


This article is a great example of the danger (to your pocketbook) of making performance decisions based on marketing hype.

Blood is normally slightly alkaline - and maintaining this pH is essential for optimal functioning of multiple metabolic enzymes. And for this reason the body has evolved numerous mechanisms to maintain this pH. Proteins that buffer the ph, kidneys, etc. To quote directly "In other words, water labeled "alkaline" doesn't override your body's natural ability to regulate pH. Your lungs and kidneys keep the pH of your blood tightly regulated between 7.35 to 7.45. Deviations from this (metabolic acidosis) can be fatal. The acid regulating process involves expelling carbon dioxide through breath and urine if your blood gets too acidic or secreting bicarbonate (a byproduct of metabolism that buffers acid). So the food and drink choices you make aren't noticeably going to change your body's pH if everything is working as it should."

There are no scientific studies on the direct effects of an alkaline diet or alkaline fluids on athletic performance. One studied rehydration in a dehydrated group of subjects and noted "..high-pH alkalized water lowered blood viscosity, the direct measurement of how efficiently blood flows through the vessels. This means blood flowed more efficiently with alkaline water and may increase oxygen delivery throughout the body during recovery." The key word in this conclusion is MAY. Just because blood has a lower viscosity means nothing about its contribution to recovery or oxygen delivery. And to quote further "...Again, this study did not reveal any health or performance benefits in those using alkaline water."

Staying hydrated is important for optimal performance and recovery. Plain water is just fine. If you want to pay a bit extra to help you keep drinking (a fluid you enjoy), then alkaline water and other sports drinks may be worth it. But aside from taste, they have no magical performance enhancing properties.


Is a minimum fluid intake per 24 hours required to "flush out toxins" and maintain health? Up until the fall of 2022, the short answer (as summarized in this NYT article was "no". That is:
  1. No evidence that increasing fluid intake decreases kidney disease.
  2. No evidence that increasing fluid intake decreases the risk of heart disease or stroke (but note: once again there is a correlation between increased coffee intake and decreased cardiovascular risk)
  3. No evidence that increasing fluid intake improves skin tone and luster.

But things changed with the publication of this prospective study of 15,000+ individual with middle-aged enrollment (45-66 years) and 25 years of follow up. Blood (serum) sodium concentration was used as a proxy for hydration habits. They found a 20% increase in the risk of death and a 40% increased risk of developing a chronic disease in those with a serum sodium at the higher end of normal serum sodium range.

Based on this study, it seems prudent to me to drink an extra glass of water each morning as part of a healthy lifestyle, just like eating well and exercising. And to focus on replacing fluid losses after a long ride. There is nothing to lose and everything to gain.


I'm not sure the following reference will provide information to make you a better cyclist, but I found the physiology fascinating. Click on VIEW TRANSCRIPT if you want to skim their content.

Blog #1

Blog #2 Blog #3 So an interesting physiology tidbit, unless you are using cycling to drop a bit of weight. No supplements or special tools needed. Just tap water, and determination. This effect will not improve your cycling speed - unless you use it to drop a few pounds.


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).

And drink when you are thirsty - not to meet a predetermined minimal daily fluid intake.

All questions and suggestions are appreciated and will be answered.

Cycling Performance Tips
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