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When muscle is cooled, it is weakened → leads to rapid fatigue

Prolonged exercise in the cold → energy supplies ↓ and exercise intensity ↓ , so ↑  susceptibility to hypothermia

Release of catecholomines increases the mobilization and use of FFA as fuels

Vasoconstriction impairs circulation to subcutaneous fat tissue

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1. Heat cramps : Excessive sweating → water and electrolyte loss

2. Heat exhaustion : Inability of the CV system to meet the needs of the active muscles and the skin

3. Heat stroke : Failure of the thermoregulatory mechanisms

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Inability to lose heat

- Higher core temperature
(Risk of hyperthermia and heat injury)
- Higher sweat rate
(May be as high as 4–5 L/hour)
(Risk of dehydration)

Can result in muscle fatigue and impaired performance

- Reduced mental drive for motor performance
- Reduced muscle blood flow
- Accelerated glycogen metabolism
- Increased lactic acid production
- Increased free radical production

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Thermal energy (also called heat energy) is produced when a rise in temperature causes atoms and molecules to move faster and collide with each other.

The energy that comes from the temperature of the heated substance is called thermal energy.

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As exercise intensity increases:

1. Heat production increase.

2. Linear increase in body temperature

Core temperature proportional to active muscle mass

3. Higher net heat loss

Lower convective and radiant heat loss

Higher evaporation heat loss

4. As ambient temperature increases:

Heat production remains constant

Lower convective and radiant heat loss

Higher evaporation heat loss

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HEAT EXCHANGE AT REST AND DURING EXERCISE

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HEAT EXCHANGE AT REST AND DURING EXERCISE

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PHYSIOLOGICAL RESPONSES TO EXERCISE IN THE HEAT

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PHYSIOLOGICAL RESPONSES TO EXERCISE IN THE HEAT

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1. Cardiovascular function

2. Energy production

3. Body fluid balance: sweating

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During exercise in the heat, increased demand of blood to working muscles and to the skin, therefore these areas are not having enough blood.

During prolonged exercise in the heat, cardiovascular drift occurs, where HR ↑ since ↓SV  due to ↑water loss, to maintain cardiac output (cardiac output = SV x HR)

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Exercise - Increases the oxygen uptake → causing working muscles to use up more glycogen and increase lactate production

Glycogen depletion and lactate accumulation cause early fatigue

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1. Rate of sweating ⬆️ → ↑ heat loss from skin → reduces skin temperature

2. Sweat is more dilute → less electrolyte loss

3. SV increases → enough blood supply to the skin and the working muscles

4. ⬇️ the rate of glycogen use → delay onset of fatigue

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1. Body size & body composition

2. Windchill increases heat loss thru conduction and convection

3. Immersion in cold water increases heat loss thru conduction

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< 34.5 °C, the hypothalamus begins to lose its ability to regulate body temperature

Hypothermia affects SA node that leads to drop in HR and cardiac output

Extreme cold decreases respiratory rate and volume

Frostbite due to vasoconstriction to the peripheral areas that ↓ blood flow hence lack of O2 and nutrients, therefore skin tissue die

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Not well studied

Repeated exposure to cold alters peripheral blood flow and skin temperature, therefore greater cold tolerance

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Electromagnetic heat wave

R Energy - Move through air to solid, cooler objects in the environment

The body absorbs radiant heat energy from the surrounding - When an object's temperature exceed skin temperature

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Direct heat transfer from one molecule to another through liquid, solid, gas

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Air movement (imagine raining against sunny day)

Less / slow air movement = ⬆️ skin temperature

High / fast air movement = ⬇️ skin temperature

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Water vaporising from the respiratory passages and skin surface continually transfers heat to environment

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Hypothermia and hyperthermia are two extreme, but equally concerning, states of temperature loss or gain.

Hypothermia - You lose more heat than your body can produce and you feel very cold.

Hyperthermia - Your body produces more heat than it can lose.

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Both the exercise itself and the air temperature and humidity can increase your core body temperature

To help cool itself, your body sends more blood to circulate through your skin

This leaves less blood for your muscles, which in turn increases your heart rate.

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1. Increase sweating can lead to dehydration and excessive electrolyte loss:

→ leads to the release of aldosterone and ADH →
function to retain the level of sodium and water.