Hot Environments

How hot is too hot? Heat advisories are

announced when a wet bulb-globe

temperature (WB-GT) is over 87° F (30.5°

C) or when temperature and humidity are

over 85° F and 60%, respectively. Under

these conditions exercise should be

performed indoors or undertaken with

caution. Any time you perform physical activities in the heat, you will lose a lot of water and electrolytes through sweat. Only the sweat that evaporates effectively cools the body; sweat that "drips" provides little cooling effect. As you adapt to the heat, you will start producing more dilute sweat (less salty) to conserve electrolytes. Factors that can limit "effective cooling" include high humidity, impermeable clothing, and skin conditions, such as sunburns or rashes.

Energy Needs

Although appetites may be suppressed in the hot weather, especially during the first few days after arriving, adequate caloric intake is very important. Inadequate food intake will lead to weight loss which can impair both physical and mental performance. When you do the same task in a hot environment, energy requirements are increased due to the increased work of maintaining a normal body temperature. When living and working in temperatures ranging from 86° to 104°F (30° to 40°C), kcal intakes should be increased by 10%, unless your activity level decreases accordingly.

If your activity level decreases, you do not need extra kcals!

 

Worksheet 12-1. Calculate Your Energy Requirements for a Hot Environment

^ л

Your Estimated Energy Requirement (EER) =_________________ kcal/day.

(from Worksheet 1 -2)

A 10% increase in energy requirements equals:

_________ EER x 0.10 =_________ kcal/day.

Your total energy requirement equals:

__________ EER +________ 10% increase=________ kcal/day.

Tips for Maintaining Performance in a Hot Environment

♦ Prepare by maximizing aerobic fitness before your exposure.

♦ Plan your workouts to avoid the heat of the day.

♦ Plan for decreased physical performance the first two weeks.

♦ Drink plenty of fluids and eat enough kcals.

♦ Be aware of any symptoms that may predispose you to
dehydration (diarrhea, vomiting, fever).

♦ Be aware of the warning signs of heat illness. Stop if signs or
symptoms of heat injury become apparent (See Chapter 13).

♦ Avoid substances that can lead to dehydration or heat injuries.

Table 12-1. Substances that Can Cause Dehydration

Caffeine Alcohol Decongestants

Antihistamines Atropine and other anticholenergics

Check with the medical department for other substances that may affect fluid balance.

Cold Environments

What is a cold environment? It is considered cold if the air temperature is below 15° F and the wind speed is greater than 25 m.p.h, or the water temperature is below 64°F. Cold wind and cold water accelerate heat loss by replacing the warm layer of air or water surrounding the body with colder air or water.

The body responds to cold by constricting (tightening) blood vessels to conserve heat and by shivering to generate heat and guard against hypothermia. There is increased urination and increased energy metabolism in cold environments, both on land and in water.

Energy Needs

Many studies have shown that soldiers tend to progressively lose weight when conducting field exercises in the cold for two to three weeks. Because significant weight loss can result in fatigue and performance decrements, energy intake must increase to meet the increased energy demands. Energy requirements can increase by 25 to 50% because of the increased work associated with performing physical tasks in the cold and the kcal expenditure due to shivering. Factors that increase energy requirements in the cold include:

♦ Increased basal metabolic rate (BMR, see page 3).

♦ Shivering.

♦ Working in cold weather gear.

To meet energy needs consume a diet that is high in CHO (roughly 60% of your total daily kcals). This will replace glycogen stores (page 7) that are being used to maintain body temperature. Eat frequent high-CHO snacks to help meet your kcal requirements. Keep fat intakes under 30% of your total daily kcals since high-fat diets may cause stomach upset. Keep protein intakes at 10% of your total daily kcals and avoid protein and amino acid supplements because high-protein intakes increase water losses.

Worksheet 12-2. Calculate Your Energy Requirements for a Cold Environment

Your Estimated Energy Requirement (EER) =______________ kcal/day.

(from Worksheet 1 -2)

A 25% increase in energy requirements equals:

_________ EER x 0.25 =__________ kcal/day.

Your total energy requirement equals:

__________ EER +________ 25% increase=_______ kcal/day.

e.g., If your EER is 3,000 kcals/day then in a cold environment your energy needs would increase by 3,000 kcals x 0.25 = 750 kcals/day. Your total daily energy requirement would be 3,000 kcals + 750 kcals = 3,750 kcals/day.