Nearly all the bio-chemical
reactions that occur in body cells depend on water and electrolyte (sodium,
potassium, calcium, chloride, phosphorous, magnesium, etc.) balance. These
balances are not only vital to maintaining life but also affect physical and
mental performance. Water is the most abundant component of the body (60 per
cent + by weight). It is believed that it was Mike Colgan of the Colgan
Institute who referred to the body as a "Hairy protein bag full of
water". This bag of water has many holes which allow for leakage. These
holes include skin pores which allow for perspiration (skin leakage) the
kidney/bladder system which expels wastes carried by water and the respiratory
system which must he moist or breathing would be very dry and painful. Adequate
hydration is very important in the maintenance of body temperature. When muscles
contract they generate heat which must be dissipated from the core to the body
surface and adequate water to maintain adequate blood volume is vital. Blood,
kidney, heart and lungs are made of 80 per cent or more water. Muscle, spleen,
brain, intestines, and skin are 72-75 per cent water. Even bones are 22 per
cent and fat tissue is 10 per cent water. On a normal, moderate temperature,
inactive day you would lose 1.5 liters (6 glasses) of water through kidney
filtration (urine production) and another 0.750-1 liter (3-4 glasses) through
the skin and respiration. So an average person needs 8-9 glasses per day just
to replace average losses. It is true you get some of that from fruits,
vegetable, other beverages and food. My "rule of thumb" for water
requirements has long been—weight in kgs./2 = gm of water/day. Caffeinated,
alcoholic and many carbonated beverages have a diuretic effect and actually
increase the daily fluid requirements. One should choose pure water or high quality
sport beverage in some circumstances. Naturally, daily fluid requirements will
vary with environmental conditions, clothing and exercise intensity and
duration.
Even mild dehydration-1 per cent
of body-which would represent approximately.75 to 1 liter of water (1 per cent
of 75 Kg = 750 ml.) can create a reduction in muscle performance and start to
show dehydration symptoms. Early symptoms are headaches, dry eyes (ask any
contact lens wearer what happens after a couple of glasses of wine), drowsiness,
loss of concentration, irritability. If the dehydration is 2-3 per cent,
serious performance inhibition occurs. Dr. David Costill demonstrated that at
these low levels of dehydration 1-3 per cent even the time for 1500 metres was
inhibited. The time for a competitive 10 K was reduced by 2.5 minutes which is
serious in a 30 min 10 K. Muscle cramps are also a sign of inadequate fluid
replacement and electrolyte loss, particularly calcium and magnesium. Even
"Lactate threshold"—an indicator of maximal work performance ability
is lowered which is not a good thing in high intensity, endurance competition.
Thicker blood, fast heart rate, negative changes in blood pressure is other
symptoms. Don't wait until you are thirsty to decide to drink. Fluid
replacement is part of a daily plan. Thirst is a sign—too late—of dehydration,
performance is already impaired. You actually lose significant fluid just
sitting in an air conditioned car or office. Frequent drinks of water during a
long automobile trip will reduce apparent road fatigue. The same applies to
sitting at your desk. A friend has a water bottle holder mounted on the dash of
car to encourage convenient hydration while driving. Here are typical water
losses during exercise: 1 hour of weight training = 227 gm; 45 minutes of
swimming = 283.75 gm, a softball game = 454 gm; 5 mile run = 681 gm, 45 minutes
of full court basketball = 681 gm; bicycling for 1 hour = 936.37 gm. and a
marathon = 3291.5 gm. As the environmental temperature, exercise intensity and
or duration increases, you need to drink more and may want to switch to a
quality sport drink (one made with a glucose polymer like maltodextrin rather
than table sugar and 6-8 electrolytes rather than just sodium and potassium) to
avoid a condition known as Hyponatremia or water intoxication caused by
electrolyte loss and excess water intake. During the famous Daedalus man
powered flight over the Aegean Sea (energy equivalent of 3 non-stop marathons)
in 1988, the athlete lost only 1.5 Kg and had normal blood chemistry at the
end. He drank a cup of high quality sport drink every 15 minutes for just over
4 hours. Cool beverages are absorbed better than room temperature or warm
beverages.
