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Thursday, 24 June 2010
Marathoners need to replenish fluids, but is there a limit?
During
a marathon, bodies sweat and fluids are lost -- even with the
thermometer in the 50s and 60s -- which could present a potential
problem for back-of-the-pack runners.
Because of this, it is a
well-accepted fact that runners should drink plenty of fluids to avoid
heat illness.
The recommendations of the American
College of Sports Medicine regarding exercise and fluid replacement are
to drink large amounts of fluid 24 hours before an event, drink 17
ounces two hours before exercise, consume fluid during exercise to
replace all the water lost through sweating, and consume the maximum
amount of fluid that you can tolerate while exercising.
However,
there may be a risk involved in drinking the maximum amount of fluid
your body can tolerate.
Sports medicine physician Dr. Timothy
Noakes, the author of the Lore of Running, argues that because race
organizers are so acutely aware of the hazards of heat illness,
typically copious amounts of fluid are available for runners, and
runners frequently are encouraged by race organizers to drink -- early
and often.
If a runner collapses, it is most likely to occur at
the end of the marathon. Noakes suggests this can be explained by a
sudden fall in blood pressure rather than dehydration. When a runners
suddenly stops running, as at the end of a marathon, the repetitive
muscle contractions in the legs stop.
This leads to a temporary
fall in blood pressure, as the muscle contractions are not available to
pump the blood back up the venous system to the heart.
Noakes
suggests both the elite athlete and back-of-the-pack runners are aware
of the importance of drinking fluid during a marathon. The elite
athlete, who is concerned with his race time, might find it more
difficult to take the time necessary to consume adequate amounts of
fluid.
For the back-of-the-pack runners, it is much easier for
them to obtain fluid, and they are often urged to "drink as much as you
can tolerate."
Whether you are a elite runner or a
back-of-the-pack runner, there is a potential problem with drinking too
much fluid. It’s called hyponatremia, an abnormally low concentration of
sodium in the blood.
The symptoms of hyponatremia include
bloating in fingers and face, nausea, vomiting, muscle weakness, cramps,
headaches and disorientation.
Hyponatremia has been called
"water poisoning." If it is untreated, it can lead to convulsions and
death.
Low levels of sodium in the blood occur frequently in
marathoners and ultra-distance athletes. There is a debate whether this
occurs because of sweating too much sodium, and/or in taking to much
water, which dilutes the sodium in the body.
The key to
preventing hyponatremia is to maintain the appropriate balance of fluid
and sodium. If your run is longer than an hour, commercially available
sports drinks will provide sufficient sodium.
However, some
experts question whether the concentration of sodium available in sports
drinks is sufficient. They suggest taking salt tablets, or eating salty
food during the endurance event. Future research should clarify how
much sodium replacement is needed.
Noakes offers a simpler
solution. Rather than seeking large amounts of sodium, he suggests that
runners drink less. He disagrees with the American College of Sports
Medicine’s Recommendation to "drink as much as you can tolerate." He
suggests "drink as much fluid as it takes to quench your thirst."
As
is frequently the case, concepts evolve. In the early ’60s, the advice
was to avoid drinking when you exercise because it will give you stomach
cramps. This concept evolved to drink as much as you can tolerate. Now,
the pendulum is swinging back to drink only if you are thirsty.
Author:
Damien Howell (18 Jun 2010) courtesy of ENTRYTIME - www.entrytime.com
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