Heat Stress Bulletin

Whether it is the air pollution or simply part of a 5 or 10,000 year cycle is unknown, but Earth is definitely getting hotter. We humans still have the same old defense systems against heat illness: raise skin temperature by raising skin blood flow; start sweating sooner; and produce more sweat. However, it takes three things for these systems to work:

1. Time for conditioning
2. Water / Hydration
3. Ability to evaporate sweat

TIME
Even an athlete in training needs time to get used to working out in the heat. It may take him only 3 to 5 days, working out for two, to at most, four hours a day in the heat (more hours won’t help, but will increase the risk). Someone out of condition may need 5 to 7 days to reach the same degree of “heat acclimatization.”

WATER
The hotter the air AND the harder the training (i.e., the more calories required for the workout), the more body water will be lost as sweat. Loss of a quart (2 lbs.) per hour is routine; losses of 2 quarts (4 lbs.) or more per hour have been measured. Note, an average man only has about 5 quarts of blood to: 1) carry oxygen to the working muscles; 2) carry heat out to the skin; and 3) provide a large part of the water lost as sweat. So, it is all too easy for the body to run low on its “radiator fluid” and overheat. Heat exhaustion collapse can occur in less than one hour; heat acclimatization and a high water intake are the two key solutions to avoid the heat illness.

These guidelines, and the following common sense suggestions, should help insure your team against heat illness problems early in the season:

1. Reduce the amount of body surface covered by clothing, particularly by impermeable plastic protective pads.

2. Schedule hard workouts for the cooler times of day.

3. Eliminate (minimize) alcoholic drinks for 24 hours before workouts in the heat.

4. Check body weight pre and post activity daily during very hot weather to be sure enough water is being taken during activity (pre and post activity weight should, ideally, be unchanged) and that there is no cumulative dehydration (day to day weight loss, if any, should not be water loss).

HYDRATION

To calculate your body’s water needs, either use .5 oz fluid per pound of body weight (bw). Or divide your weight in pounds by 2.2 to find your kilograms body weight. Then multiply it by 49: to convert ml to oz divide by 30.

Example:
200 lb. Male needs:

16 oz cups X 9
12 oz cups X 12

Step 1: 200 / 2.2 = 90.0 kg

Step 2: 90.0 x 49 ml = 4454 ml

Step 3: 4454 / 30 = 148 oz