Hydration used to be one of the
simplest lessons in running and walking training: drink as much as you can, and
then drink some more. Nowadays, new research and new dangers have compelled the
hydration experts to reconsider the decades old advice about hydration. For a
long time we knew that not drinking enough could cause
performance degradation, injury, and even death. We now know that it is also possible to drink too much
and also cause performance degradation, injury, and death.
This “new” risk of drinking too
much is known as hyponatremia. Hyponatremia is a condition where the salt
content in your body is depleted to critical levels. When the salt (or sodium)
levels become too low, a variety of events result over time which can lead to
the lungs filling up with fluid and more seriously, brain swelling. This can
lead to seizures, coma, and even death. In marathoning, this condition is
caused when runners drink much along the course and dilute sodium within the
body to very low levels. In trying to prevent dehydration, we overcompensate
and cause an “overhydration” state.
There are numerous studies on
ultra-runners, ironman triathletes, hikers, and military personnel documenting
fluid overload as the primary risk factor toward the development of
hyponatremia. Preliminary data from the Houston Marathon, publication pending,
suggests that runners who are developing hyponatremia are drinking excessive
amounts of fluid when more moderate fluid intakes would be adequate to complete
the marathon successfully.
In the recent Honolulu Marathon,
it was 73F at the start with a high temperature of 82F (much hotter than the
previous Houston Marathons). There were over 19,000 finishers, average
finishing time around 6 hours. Remarkably, no hyponatremia was reported that
day. There are only 12 water stops along the Honolulu course. In the Houston
Marathon, we have 30 water stations and probably the most reported number of
cases of hyponatremia in the country.
In short then, runners and
walkers must learn to drink the right amount of fluids. The best way to learn
what the “right “ amount of fluid is for an individual is to weigh yourself
without clothes before you run and then again after you run. Make sure to towel
off before the second weigh-in. The difference in weight is a fair
representation of the fluid lost. Drink
16 oz. Of fluid, preferably with some sodium, for every pound of weight lost.
If you have gained weight, you are over-hydrated. Do not feel compelled to
“force” fluids at any time.16oz – 28oz of fluid per hour is advisable. Protect
yourself against dehydration, but be wary of hyponatremia as well. Be
especially concerned if you are a woman, and/or are on the course for more than
4-5 hours.
HYPONATREMIA
What Is It?
Hyponatremia (low blood sodium)
is a dangerous and potentially fatal condition. It can result from drinking too much water during prolonged
exercise. Sodium is lost from the body through sweating, so in hot humid environments
and /or when exercising for long periods of time, sodium replacement is as
crucial as fluid replacement before, during, and after endurance activity.
Hyponatremia can exhibit such
symptoms as nausea and vomiting, weakness, incoordination, severe headaches,
puffiness, disorientation and confusion. Difficulty breathing, seizures, and
even death may occur as well. This condition often occurs a few hours AFTER
endurance activity ceases.
How To Prevent It:
In hot and humid conditions or
when exercising over one hour, replenish fluid loss with beverages containing
electrolytes. Water alone is ineffective as it can reduce the stimulus to drink
as well as cause increases in urine production (and, hence, further fluid
loss).
Salt your foods. Ingesting
excess sodium is rarely a problem if volume intake is sufficient and kidney
function unimpaired.
Determine individual rates of
fluid loss by weighing yourself before and after a run after toweling off the
sweat. This is the most accurate way to
prevent over and under hydration during and after long runs and races.
If you are going to be
exercising for more than four hours, try experimenting with salty snacks (i.e. pretzels, saltines) when you get
hungry during the run.
Avoid using pain relievers and
anti-inflammatory medications during endurance activity.
DEHYDRATION
What Is It?
Inadequate fluid intake, or
dehydration, can lead to diminished performance, premature exhaustion, and
serious health consequences, including death. The most serious effect of dehydration
is impaired heat dissipation, which can elevate body core temperature to
dangerously high levels, resulting in heat exhaustion and potentially fatal
heat stroke.
The symptoms of heat exhaustion
include: cool, moist, and clammy skin, heavy sweating, low blood pressure, high
pulse, dilated pupils, headache, nausea, confusion and collapse.
Treatment for both includes
rapid cooling and rehydration. If heat stroke is suspected, call for medical
assistance immediately.
How To Prevent It:
Stay hydrated. Drink about two
cups (500ml) of fluid two hours before exercise to promote hydration and allow
time to excrete excess ingested fluids. Continue to drink approximately 16oz
-26oz of fluid per hour of exercise.
Thirst is not a good indicator
of fluid balance. Changes in body weight are more accurate in gauging how much
fluid you lost and how much fluid needs to be replaced. Weigh yourself prior to
a run. At the end of the run, weigh
yourself after toweling off the sweat.
For activities lasting over one
hour, beverages containing 6-8% carbohydrate and electrolytes are recommended
for hydration.
The following conditions may
increase your risk for heat illness: obesity, low fitness level, lack of heat
acclimatization, sleep deprivation, use of diuretics or antidepressants; or a
recent illness with fever, diarrhea, or respiratory symptoms.