Mild Dehydration Does Not Impair Exercise Performance
The Gatorade Sports Science Institute in Barrington,
Illinois published a study showing that 46 percent of recreational
exercisers are dehydrated (Applied Physiology, Nutrition and
Metabolism, June 2006). However with good reason, the study
does not say that they are harmed. There is no data anywhere
to show that this mild dehydration affects health or athletic
performance. Another study from the University of Connecticut
shows that a person must lose a tremendous amount of fluid
before it affects his performance (Medicine & Science in Sports &
Exercise, October 2006).
When you exercise for more than an hour, you may need
to take fluid, but not too much. Excessive fluid can cause a
potentially fatal condition called hyponatremia. Normally, the
amount of salt and other minerals in your bloodstream should
equal the same total mineral content in every tissue in your body.
If the mineral concentrations are not equal, they try to become
equal. Fluid moves from the area of lower mineral content to that
of the higher concentration. If you take in so much fluid that it
lowers the mineral level in your blood, levels in your brain are
higher than those in your bloodstream. This causes fluid to move from
your bloodstream into your brain, which increases pressure in
your brain and can cause seizures and unconsciousness. The
swelling can cause permanent brain damage.
Hyponatremia is a disease seen almost exclusively in
people who are not exercising near their maximum. The major
risk factor is having more time to drink than to concentrate on
pushing the pace, no matter what the sport or the duration of the
event. Top athletes drink very little fluid during competitions such
as bicycle racing, marathon running or cross country skiing,
because it is so difficult to drink while you are exercising near
your maximum. On the average, a world-classes marathon
runner drinks less than a cup an hour during a race. This is far
less than the amount recommended by the American College of
Sports Medicine just a few years ago. On the basis of our
present knowledge, it may not be safe for mediocre athletes to
take in more than 800cc per hour (3.5 cups).
Recent studies show that fit humans can tolerate
significant fluid loss before their performance suffers, and that
most cases of muscle cramps are not caused by dehydration or
salt loss. They are caused by muscle damage itself and can be
controlled by stopping exercise and stretching the cramped
muscle.
Checked 9/29/08