Fun in the Sun Means Proper Preparation
The most dangerous condition for exercisers, Martin says, is humid heat. The
evaporation of sweat helps to cool the body, but humidity limits the amount of
evaporation, he explains.
If you're exercising, that can be critical. Most of the perspiration we
produce comes from blood plasma. So excessive perspiration can decrease the
volume of blood just when it is needed in the muscles that are working.
In times of heat stress, the body also sends blood to the skin surface to
cool the body by radiant heat loss. "But at the same time, you want that
same amount of blood to go into your working muscles, so that you can provide
nutrition and oxygen for metabolism. And if you have to share a smaller and
smaller amount of blood, because of sweating, with these two major tissue
masses -- the skin for cooling, but the muscles for working -- something has to
give," Martin says.
This could hurt the athlete's performance, or it could lead to heat
exhaustion or even heat stress. A person racing in the heat, for instance, can
lose a liter to a liter and a half of sweat an hour. But the body can absorb
about a liter of water an hour, so adaptations are necessary for those who must
compete or work in the heat.
"One of the training adaptations is that training in the heat stimulates
storage of more fluid, so your fluid volume increases so you have more
available," Martin tells WebMD. But that kind of training needs to progress
gradually. Martin says it usually takes about a month for an exerciser to
"acclimatize" to the heat.
Most sports drinks do work, according to Martin, as long as they aren't too
high in carbohydrates, "because this can actually lessen fluid
absorption." He says exercisers should stay away from beverages that
contain alcohol or caffeine because they can be dehydrating.
So if preventing and rectifying heat exhaustion is as simple as drinking
enough fluids, why do overheated people keep showing up in emergency rooms?
Maintaining healthy hydration (and the all-important healthy diet) doesn't
always go according to plan, Martin says. "It sounds so simple; it's
amazing that it's so difficult to do."