by Deborah L.
Most people realize they sweat more when they exercise and that in order to stay
healthy, they need drink water. However, many people aren't aware of how much water they
need to drink and why it's important to so.
When engaged in physical activity, body temperature rises as much as 3 degrees. Your
body's natural cooling system, sweating, kicks in to lower body temperature. Under extreme
exercise and heat stress, a body can lose 1/2 a gallon of water per hour. If the lost
water is not replaced, dehydration occurs and serious consequences may follow.
To understand what happens, I'll use the analogy of your car. When your car's cooling
system is running smoothly, excess heat from the engine is transferred to the water in the
tubes, which goes to the radiator to be cooled by the air. The cooled water goes back to
be heated once again by heat drawn from the engine. If there is not enough water in the
system to allow for proper heat dissipation, your engine overheats, your car stops
running, and you are left cursing at the side of the road.
Now picture your body as the car-- your muscles are the engine, your skin is the
radiator and your blood vessels are the water tubes that connect the engine with the
radiator. When your cooling system is running smoothly, excess heat from your muscles is
drawn into your blood vessels where is circulates to your skin. Evaporating sweat draws
heat away from the blood vessels. The cooler blood then recirculates throughout the body,
lowering body temperature.
When too much water is lost through sweating, your blood volume decreases. This
decreases blood pressure which, in turn, reduces blood flow between the muscles and skin.
To overcome this, your heart rate increases. Because less blood reaches the skin, heat
loss is reduced and the body overheats. Just like your car, your body can quit running.
If you fail to replace the water you lose, you run the risk of becoming dehydrated.
When a person is dehydrated by more that 4% or 5% of body weight, their exercise
performance declines by 20% to 30%. Not only that, the impact of dehydration on the
cardiovascular system can produce heart problems in people with coronary heart disease and
diabetes. Dehydration is also hard on the kidneys.
How do you prevent your body from "breaking down"? It's simple. You need to
put in as much water as is going out. Sweating is not the only way you lose water. Another
is through respiration-- you lose water every time you exhale. This water loss increases
as your physical activity increases because you breathe more. So if you are just replacing
how much you are sweating out, it's not enough. Also if you just drink when you are
thirsty, you aren't getting enough water because thirst alone isn't the best measure of a
body's fluid needs.
Generally speaking, you should drink water before, during, and after exercise. Drinking
about 2 cups (16-oz.) of water one hour before, and 1 cup 1/2 hour before is a good start.
Then you should drink 1/2 cup to 1 cup or more, every 15-20 min. The amount depends on the
air temperature, your body weight and how hard you are exercising. Drink up! Show the
people you exercise with that you know how to keep your body running!