Maybe this happened to you in the academy. A grizzled, veteran police officer stood up in front of your PT class and told you that as part of your training you would have to run four miles in 103-degree heat without stopping for water. His reason for such an order was academy tradition. That's how he did it in the academy, so you'd better be able to tough it out. And if you can't deal with it, then maybe you can't hack it as police officers.
That run was brutal, and you'll remember it all of your life. You made it, but others weren't so lucky. Some of your fellow cadets started feeling dizzy and nauseous, and then started collapsing before they reached the end.
It may seem obvious to everyone but old-fashioned football coaches, drill sergeants, and police academy PT instructors, but people exerting themselves in the hot sun need water. You need water for your body to function normally, and when your body is excessively hot, you need even more. To do your job and, in fact, to stay alive, you need to replace the water and electrolytes you use up by exerting energy. Whether you notice it or not, simply existing uses up water.
The goal of hydration is to provide the body with water, sodium, potassium, chloride, and bicarbonate in order to maintain a state of normal homeostasis. So it's not just water that keeps your body hydrated, but the electrolytes that help balance out your body's fluids.
Basically, the stuff in water keeps your body in working order-as long as you get enough of it. In addition, sufficient calories are needed to minimize body protein catabolism. Normal maintenance requirements provide water and electrolytes to replace those that are lost through urine, stool, and even through breathing and sweating.
In one day, a 155-pound male loses about 1,000 to 1,500 milliliters (ml) of water through urine, and about 1,000 ml of "insensible" water: 300 ml through the skin and 700 ml through breathing.
When your body becomes dehydrated, it is less able to dissipate the heat that it naturally produces. This can lead to rapid elevation in body temperature and heat exhaustion. Medical studies have demonstrated that even a 1-percent decrement in hydration can result in decreased physical and mental performance. At 7-percent dehydration, exhaustion and collapse are imminent.
Heat exhaustion occurs because blood volume displacement to the skin causes marked cardiovascular stress. In the on-duty police officer, heat exhaustion can lead to headache, dizziness, nausea, diminished fine motor function, and confusion. If not treated this can progress to heatstroke, which is a true medical emergency, and life threatening if not treated.
In hot weather, an officer should be well hydrated before beginning his or her shift. The American College of Sports Medicine recommends that individuals drink 500 ml of fluid about two hours before physical activity to promote adequate hydration and allow for excretion of excess water. In general, replacing body fluid losses through drinking (we're talking water, here) can prevent dehydration.
Depending on thirst to tell you when to drink water often results in significant dehydration. Thirst provides a poor index of body water needs. If you're thirsty, you're probably already dehydrated.
A person can dehydrate by 2 to 8 percent of his or her body mass during physical activity. Believe it or not, about 60 percent of body mass is water. Dehydration of 2 to 8 percent is equivalent to a loss of 1 to 4 liters of body fluids for a person of 163 pounds body mass. That's a lot of water to be missing.
But your body's rate of water loss could vary based on several factors. The sweat rate, which greatly affects your rate of dehydration, is a function of individual metabolic rate, clothing, and climatic conditions-all of which change often.
Medications can also play a role in daily water loss. An officer taking medication such as thyroid replacement hormones or diphenhydramine (Benadryl) for allergies may be at risk because these and other medications can interfere with thermoregulation.