HOW MUCH FLUID SHOULD I DRINK DURING
IMMDA’s REVISED FLUID RECOMMENDATIONS FOR
RUNNERS & WALKERS
committee: Lewis G. Maharam, MD.FACSM (chair),Tamara Hew DPM, Arthur Siegel MD,
Marv Adner, MD, Bruce Adams, MD and Pedro Pujol, MD, FACSM
IMMDA: 6 May 2006. Barcelona, Spain
As Medical Directors (IMMDA: International Marathon Medical
Director’s Association) of the world’s largest marathons and endurance events,
it is our desire to educate and ensure that our participants consume proper
fluids and amounts of fluids during endurance events to remain healthy and
perform well. Too much or too little may bring about health concerns and/or poor
performance. We therefore offer the following guidance for runners and walkers
at all levels to follow in their training and competitive events.
What should you drink?
The evidence on this is
clear. If your event or workout is longer than 30 minutes you should be drinking
a sports drink. The added carbohydrate and electrolytes speed absorption of
fluids and have the added benefit of energy fuel and electrolytes. There is
actually decreased benefit to watering down or diluting sports drinks or
alternating sports drinks with water.
How much should you drink?
Drinking too much or too
little can be of risk to health and performance. Hyponatremia ( low blood salt
level due to abnormal fluid retention from overdrinking) and dehydration (due to
net fluid losses from under drinking) are conditions easily adverted by
understanding your individual body needs. Just as you have a unique face and
fingerprint, your body’s need for fluid is individual as well. Body weight,
gender, climate, sweat rate are just a few variables that individualize your
needs. Understanding that it is normal to lose a small amount of bodyweight
during a marathon race: bodyweight will re-equilibrate over the next 24 hours
through the consumption of sodium and fluids with meals. A weight loss of
more than 2% or any weight gain are warning signs that justify immediate medical
consultation and indicate that you are drinking improperly.
We offer the following ideas and guidelines for you to
consider as you assess your individual fluids:
Try to drink to thirst. This advice seems way too
simple to be true; however, physiologically the new scientific evidence says
that thirst will actually protect athletes from the hazards of both over and
underdrinking by providing real time feedback on internal fluid balance. If you
are not thirsty, try to refrain from drinking. Do not feel compelled to
drink at every fluid station nor follow the cues of other runners: their fluid
needs are probably very different from your own. If you are “over-thinking” and
feel you cannot rely on this new way of thinking, experiment in your training
with one of these other ways realizing each has it’s own cautions as well.
OF FLUID REPLACEMENT *
should understand that there are individual variations: “one size does not fit
all”. We endorse thirst as the best scientifically supported method for you to
use. These alternate methods may not take into account changes in ambient
conditions, running speed and terrain which can all change dynamically which
thirst as a method to use does.
Runners and walkers who are interested in the endurance
“experience” rather than pursuing a ‘personal best’ performance, must resist the
tendency to over drink. Runners/walkers planning to spend between 4-6 hours or
longer on the course are at risk for developing fluid-overload hyponatremia and
usually do not need to ingest more than one cup (3-6 oz: 3 oz if you weigh
approximately 100 lbs and 6 oz if you weigh approximately 200 lbs) of fluid per
mile. Athletes should avoid weight gain during an event.
Some participants may find that adjusting their intake to
pace or time is easier for them as shown below but remembering thirst is the
|Fluid Intake Total
|< 4 hours
||10-12 oz / 20minutes
|< 8 minutes/mile
||30-36 oz / hour
||8 oz / 20 minutes
||24 oz / hour
||750 ml / hour
|> 5 hours
||4-6 oz / 20 minutes
||2.5- 3.0 liters
|> 10 minutes/mile
||18 oz / hour
Adjust the rate of fluid intake to race pace: slower
race pace = slower drinking rate; maximum intake of 500 ml/hr (4-6 oz every 20
min) for runners with greater than 5 hour finishing times (10-11 min/mile pace).
Weight monitoring is also important: if you gain weight during your workout or
event, you are drinking too much!
For a more highly motivated runner/walker who desires a
numeric “range”, a fluid calculator can provide an estimate of body fluid
losses as a generalised strategy for fluid replacement. Participants
concerned about peak performance are advised to understand their individualised
fluid needs through use of this fluid calculator but ALWAYS defer to physiologic
cues to increase fluid intake (thirst, concentrated dark urine, weight loss) or
decrease fluid consumption (dilute or clear urination, bloating, weight gain)
while participating. It is also important to recognize that if you use this
method in one climate and then travel to a different climate for your event, the
humidity will change your sweat rate and therefore your fluid needs
Fluid calculator: to calculate sweat rate, runners/
walkers should follow these steps:
- Weigh nude before the run.
- Run/walk at race pace for one hour. (One hour is recommended to get a
reliable representation of sweat rate expected in an endurance event.)
- Track fluid intake during the run or walk; measure in ounces.
- Record nude weight after the run/walk. Subtract from starting weight.
Convert the difference in body weight to ounces.
- To determine hourly sweat rate, add to this value the volume of fluid
consumed (in Step 3).
- To determine how much to drink every 15 minutes, divide the hourly sweat
rate by 4. This becomes the guideline for fluid intake every 15 min of a
- Note the environmental conditions on this day and repeat the measurements on
another day when the environmental conditions are different. This will
give you an idea of how different conditions affect your sweat rate.
Good luck in your training. Experimenting with your fluids
can be a fun exercise. Remember to keep in mind that the consumption of
beverages and foods containing sodium or carbohydrate should be guided by the
goal to minimize loss of body weight and prevent weight gain.
The International Marathon Medical Directors Association (IMMDA) was formed as
the Consulting Medical Committee of the Association of International Marathons
(AIMS). The purpose of IMMDA is to i) promote and study the health of long
distance runners, ii) promote research into the cause and treatment of running
injuries, iii) prevent the occurrence of injuries during mass participation
runs, iv) offer guidelines for the provision of uniform marathon medical
services throughout the world, and v) promote a close working relationship
between race and medical directors in achieving the above four goals.
For further information, please contact Lewis G. Maharam, M.D., FACSM, Chairman
IMMDA Board of Governors at 24 West 57th Street, Suite 509, New York,
NY 10019, 212-765-5763, firstname.lastname@example.org.