Environmental challenges and exercise performance

What happens to our body if our body temperature increases?

Increased body temperature can denature body proteins

How does muscle contractions generate a lot of heat?

The body converts food energy into ATP and the rest is used as heat

What is thermoregulation?

The ability of the body to maintain a constant internal temperature.

Which part of the brain acts as the body’s thermostat?

Hypothalamus

What three factors determine thermoregulatory stress?

Ambient temperature, relative humidity, and wind speed.

What is the Heat Stress Index?

An index combining temperature and humidity to measure physiological stress.

What are three physiological responses to heat stress?

Increased sweating, increased heart rate/cardiac output, and vasodilation.

What is heat gain by radiation?

Transfer of heat energy through the air without physical contact (e.g., sun heating the earth).

When is radiation ineffective for cooling the body?

When the environment is hotter than the body.

What is heat loss by conduction?

Heat transfer through direct contact between molecules (solid, liquid, or gas).

What determines the rate of conductive heat loss?

The temperature gradient between two objects.

How does convection affect heat loss?

Slow convection reduces heat loss; fast convection increases heat loss.

Why is evaporation the primary defense against overheating?

When environmental temperature exceeds body temperature, radiation, conduction, and convection are ineffective or may add heat.

How does humidity affect evaporative cooling?

High humidity reduces evaporation, making sweat less effective and leading to wasted water loss.

Why is 100°F in Arizona more tolerable than 100°F in New Orleans?

Lower humidity in Arizona allows sweat to evaporate and cool the body, while high humidity in New Orleans hinders evaporation.

How does heat affect heart rate and cardiac output?

Heat increases heart rate and cardiac output

Why does blood flow redirect to the skin during heat stress?

To dissipate heat and cool the blood

What are two ways the body responds to heat?

Reddens the skin and flushes complexion

How does body composition affect heat loss?

Larger body mass = more heat production and less skin surface area per mass. Body fat insulates and hinders heat loss.

How does physical fitness affect heat tolerance?

Greater fitness = greater cardiac output = better ability to dissipate heat.

What are heat cramps?

Painful, involuntary muscle contractions during or after intense exercise in heat, often with normal core temperature.

What causes heat cramps?

Dehydration, electrolyte imbalances (sodium deficit), and neuromuscular fatigue.

What is heat syncope?

Fainting, dizziness, or lightheadedness due to heat, often from prolonged standing/sitting or after activity.

What causes heat syncope?

Excessive peripheral vasodilation, blood pooling in legs, reduced venous return, dehydration, and reduced cardiac output.

What is heat exhaustion?

A heat illness caused by heavy sweating, dehydration, sodium loss, and energy depletion in hot/humid conditions.

What are the symptoms of heat exhaustion?

Muscle cramps, weakness, pallor, fainting, dizziness, headache, hyperventilation, nausea, diarrhea, low urine output, core temp 36–40°C.

What is exertional heat stroke (EHS)?

A medical emergency where the body fails to dissipate heat after intense exercise, core temp > 40°C (104°F).

What are the signs of EHS?

Tachycardia, hypotension, sweating, hyperventilation, altered mental state, diarrhea, seizures, coma.

How is EHS treated?

Rapid cooling of body

How does fitness level affect heat illness risk?

Greater fitness = lower susceptibility to heat illness.

How does age affect heat tolerance?

Cardiovascular decline with age reduces cardiac output and heat tolerance.

How does heat affect endurance performance?

As heat increases, endurance performance declines.

What can improve performance in the heat?

Acclimatization, proper hydration, physical conditioning, and cooling methods.

What is hypohydration?

A state of reduced body water, which can reduce strength, power, and muscular endurance.

What are key adaptations during heat acclimatization?

Lower core temp at sweat onset, more dilute sweat, increased plasma volume, lower heart rate, improved exercise economy.

Why is pre-exercise hydration important?

Sweating cools the body but dehydrates it; hydration helps maintain blood flow to muscles and skin.

How does mild hypohydration affect women?

Decreased concentration and mood, increased perceived exertion, headaches.

How does mild hypohydration affect men?

Decreased vigilance and memory, increased tension, anxiety, and fatigue.

What is hyponatremia?

A condition of low blood sodium, often from overhydration (hyperhydration).

Where are cold receptors located in the body?

Skin, abdominal viscera, and spinal cord.

What is the body’s primary response to cold to conserve heat?

Vasoconstriction.

How does the body increase heat production in cold stress?

Through shivering and increased thyroid hormone (raising RMR).

What is piloerection?

Hair standing up (goosebumps) in response to cold.

What defines Stage 1 hypothermia?

Loss in ability to perform complex motor task and breathing becomes rapid and shallow

What happens in Stage 2 hypothermia?

Neuromuscular function declines due to reduced nerve conduction and blood flow.

What happens in Stage 3 of hypothermia?

Body systems shut down, organ fails, brain dies

How does cold affect fast-twitch muscle fibers?

Reduces force production.

What is EIB?

Exercise-Induced Bronchoconstriction—narrowing of airways during exercise, often triggered by cold air in asthmatics.

What behavioral adaptation helps in cold environments?

Layering clothing, proper warm-up, psychological endurance.

What physiological adaptation is seen in Eskimos related to cold?

Higher basal metabolic rate.

Who might benefit from pre-cooling?

Endurance athletes performing in hot environments.

Does cold exposure increase or decrease sweating?

Decrease sweating