Hydration & the marathon: how much to drink?

Editor's note: This post was written by Elizabeth (Izzie) Brown, M.S., R.D., C.S.C.S. Izzie teaches sports nutrition at San Jose State University. Izzie has coached the Women’s Rowing Programs at Mount Holyoke College and Temple University. In 1995 she earned a silver medal at the Pan American Games in Argentina in the lightweight women’s double rowing event.


Nutrition for a the marathon: Part 1 - Hydration

To successfully row and paddle the Petaluma Marathon greatly depends on appropriate training and nutrition. This article is the first of two. Currently, discussion includes the importance and how to’s of hydration. The second article will address carbohydrate, protein and fat consumption necessary for successful completion of this 26-mile event.

Dehydration, defined as more body water lost than consumed, compromises performance by inhibiting one’s ability to dissipate heat. When body temperature rises too much, proteins, including enzymes, cook and become ineffective. Think of cooking an egg and how the protein changes or denatures. This same type of change happens when body temperature rises above 104 degrees F, which is not uncommon during exercise. Performance is compromised when as little as 2% body weight is lost. An athlete weighing 180 lbs experiences a decrease in performance with a 3.6 lb loss during a workout or race. An athlete weighing 135 lbs experiences a decrease in performance with a 2.7 lb loss during a workout or race.

A discussion of what to do comes next and a discussion of why to do it follows that.

What to do

For a great marathon performance, match fluid lost with fluid consumed. To do this, consider fluid consumption before, during and after the marathon. In addition to quantity of fluid consumed, timing and type of fluid is important.

Before the marathon: Drink enough fluid of any kind, except alcohol-containing fluids, until urine is nearly clear and fairly frequent. A pre-event meal should include plenty of fluids and watery foods – fruit, juice and caffeine-containing beverages, as desired. Drink 16 ounces (oz.) just prior to start of race.

During the marathon: Keep in mind thirst and the desire to drink does not match body-water requirements. Thirst is usually triggered when 2% of body weight is lost, an already compromised state. Numerous researchers have demonstrated volitional drinking (drinking when and as much as the athlete wants) during exercise in the heat does not meet needs. So, knowing the amount and frequency of fluid needed, will improve performance. Athletes have two options, which are either use established sweat rates for most athletes or calculate your own sweat rate. See below to calculate individual sweat rate. General guidelines include taking 8 oz. (one cup) of fluid every 15 minutes of exercise. Athletes who are heavy sweaters should consume more. Those who sweat less, compete at a lower intensity, if temperature is cool or humidity is low, less than 8 ounces four times an hour may be adequate.

The nature of rowing and paddling makes drinking (and urination) during an event difficult. Stopping to drink from a water bottle every 15 minutes (min) may impede progress (although not drinking will absolutely impede progress and stopping on a regular basis may provide reasonable mental and physical breaks necessary to complete 26 miles). An alternative to consider would be wearing a hydration system on one’s back (Camelback for example). The rower or paddler could drink easily with minimal interruption of rhythm. Also, consider an ice-filled hydration system. What better way to stay cool than to wear an ice pack on one’s back?

The challenge when using a hydration system is knowing how much fluid is consumed. With a water bottle it is easy. A 22 oz. bottle should last most athletes 30 min or so, depending on the athlete. How will the athlete using a hydration system know when enough has been consumed? Consider doing a test. Pour 8 oz. of fluid into a cup. Place the hydration system hose into the cup and count how many seconds it takes to suck 8 oz. Plan to suck on the hose for that many seconds every 15 min during the race.

Some veterans of rowing marathons have designed ways use the bladder from and flexible hoses that allow them to drink without stopping and also keep weight off their back. Perhaps another article in this series will explain that design.

After the marathon: Drink until urination is frequent and urine is nearly clear.

Type of beverage

Coffee before the race? For many years, caffeinated beverages were taboo for athletes due to their diuretic effect. More recently it was determined that, while caffeine is a diuretic, it is not nearly as detrimental as once believed. Researchers have demonstrated that 2/3 of a caffeinated beverage contributes to hydration. Thus, if one consumes 12 oz. of coffee, 8 oz. will go toward promoting hydration. So drink caffeine-containing beverages, if desired. Caffeine may even provide an ergogenic effect, allowing the race to feel easier than it really is.

During the marathon, drink sports drinks. Sports drinks, either branded or homebrew, are essential. Examples of branded products are Gatorade, Powerade, or Allsport (6% sugar solution). A combination of sports drinks and water would be a second choice.

Why sports drinks? Because in addition to sugar, they contain contains sodium, potassium and chloride. These electrolytes accelerate the liquid absorption into the blood stream faster than water. Also, the flavor will promote consumption more than plain water.

There has been some press coverage of crises and even death from drinking too much water in a marathon. These are extreme cases, and one should be aware that the culprit is too much water, not too much liquid. Water without sodium and potassium salts dilutes the salts in the bloodstream, and that dilution of sodium is the source of the problem.

Why athletes need to stay hydrated

Ambient temperature, relative humidity, wind velocity and solar radiation contribute to body temperature changes. Factors that increase body temperature above that generated by exercise include high ambient temperature, above body temperature, through convection and conduction and solar radiation both directly from the sun and reflected off the water. Factors that lower body temperature include evaporation of sweat and conduction and convection from air and wind passing by exposed skin. The most effective method of cooling is evaporation. Think of how one’s skin feels when being swabbed with alcohol before blood donation or shots. Evaporation, however, is inhibited when relative humidity is high. Humidity is a measure of how much moisture is present in the air. When water content in the air is low, evaporation of sweat occurs (think of osmosis) and results in cooling. When water content in the air is high, little evaporation thus little cooling occurs. So imagine a dry cool breezy race day and cooling will occur readily. If race day is cool with fog and no wind, cooling by evaporation will not occur. Add to this day, the burning off of fog after one hour and then a slight breeze with an increase in ambient temperature, evaporation, convection and conduction will occur but adequate fluids must be consumed to allow heat dissipation.
Wear light colored clothing that wicks moisture away form the skin for evaporation. Poor ventilated clothing can create a humid environment next to the skin even on dry days. The direction of wind also makes a difference in cooling. Moving into a head wind promotes cooling through convection and conduction; in a tail wind cooling by convection and conduction is inhibited. When cooling is inhibited, sweating will increase in an attempt to dissipate heat, making appropriate hydration even more important.

Determining Sweat Rate
For those who want more personalized information about how much fluid to consume, determine your sweat rate. To a great extent sweat rate depends on exercise intensity, ambient temperature and humidity. So, when determining sweat rate, pick a day and a workout (race pace workout but not of race duration) that most closely matches conditions on race day.
1) Weigh yourself naked right before your workout and write it down.
2) Workout at the intensity you plan to race at.
3) Drink fluids as you normally would.
4) Weigh yourself naked after working out.
5) Subtract your post-exercise weight from your pre-exercise weight. This represents water weight lost during a workout.
6) If you drank during your workout, weigh how much you drank. (remember that 16 oz. water weighs 1 lb. )
7) Add weight of fluids consumed to water weight lost during exercise (#5).
8) Convert duration of workout into hours.
9) Divide water weight lost by workout duration in hours.
10) Convert lbs of water back into oz. by multiplying by 16 oz. The resulting figure represents sweat rate in oz. per hour. Simply match intake during the race to sweat rate to promote thermoregulation.

Example:
180 lbs (pre-exercise weight) – 175 lbs (post-exercise weight) = 5 lbs water lost
Consumed 22 oz. water bottle during = 1 _ lbs
Total water lost = 6 _ lbs
90 min workout or 1 _ hours: 6 _ lbs / 1 _ hours = 4.3 lbs per hour sweat rate
4.3 lbs x 16 oz. = 69 oz must be consumed to match fluid losses.

This represents slightly more than 3 water bottles each hour. Few athletes will carry that much fluid during a workout but to successfully complete the marathon, challenge yourself to do so and watch a terrific race unfold.