Environmental conditions - heat

Question 1

What are the different environmental conditions to consider?

Answer 1

1. Temperature-Hot/cold
2. Humidity-Wet/dry
3. Altitude/sea level

*referred to as “range of temp”

Question 2

What is ambient temperature?

Answer 2

The temperature of the environment the athlete is performing in.

Question 3

What is core temperature?

Answer 3

The temperature inside the athletes body.

Question 4

How does the body use blood as a thermoregulator of body temperatures?

Answer 4

• If the body needs to lose heat, vasodilation (blood vessels to the skin surface increase their diameter) takes place, increasing blood flow to the skin so heat loss can occur via sweating
• If the body is trying to retain heat, vasoconstriction (blood vessels to the skin decrease their diameter) occurs and less blood is sent to the skin surface so heat loss is minimised. Vasoconstriction can result in a loss of fine motor skills.

Question 5

4 methods of heat gain

Answer 5

Hormones
Environment
]Muscular activity
Basal metabolic rate

Question 6

4 methods of heat loss

Answer 6

Radiation
Conduction
Convection
Evaporation

Question 7

What is conduction?

Answer 7

Heat exchanged by 2 objects in contact.

Factors that determine rate at which conduction occurs
The difference in temp between 2 surfaces (heat flows from hot to cold)
Surface area (↑SA→ ↑ heat loss)
Thermal conductivity of the material (metal – good conductor of heat)

Question 8

What is convection?

Answer 8

Heat exchanged by contact with a fluid that is flowing.

•This will occur when heat is carried away from the body by air or water currents.

•Magnitude of heat loss is dependent on

• Speed and temperature of the air/water e.g., heat loss occurs faster as the breeze gets stronger.
• The layer of warm air which continually surrounds our body is continually displaced by cold air when the air temperature is lower than skin temperature
• By wearing appropriate clothing, athletes can promote heat loss by exposing more of their body surface area to the cooler surroundings.

Question 9

What is radiation?

Answer 9

Occurs when heat is transferred from a warmer body to the surroundings without physical contact.

•When exposed to sunshine, people absorb radiant heat energy when surroundings are hotter than their core temperature.•Radiation accounts for 60% of heat loss from the body at rest on a cool day

Question 10

What is evaporation

Answer 10

Is the cooling of the body as a result of the vaporisation of sweat.

• When the body exercises, muscles create heat.
• To avoid overheating the body uses blood to help regulate temperature
• Heat is transferred to the skin’s surface via the blood where it is released as sweat
• Increased blood flow to the skin occurs as a result of vasodilation of blood vessels
• Evaporation of sweat on the skin creates a cooling effect
• As a result, the cooled skin cools the blood travelling to the skin’s surface, maintaining the body’s core temperature

Question 11

What is evaporation dependent on?

Answer 11

• Evaporation is dependent on activity levels and environmental conditions
• Evaporation is most effective in dry conditions
• As humidity increases, evaporation becomes less effective
• 100% humidity results in no heat loss via evaporation as sweat cannot be evaporated off the skin if the surrounding air is already saturated.
• Body will continue to sweat but no heat loss occurs, and core temperature will rise.
• Dehydration becomes a problem due to a large volume of fluid being lost from the body.

Question 12

What is the rate of sweating dependent on?

Answer 12

• Rate of sweating is dependent on;
• Gender (male more than female)•Number of sweat glands
• Body surface area (↑SA = ↑ sweat)•How fit you are (↑fitness = ↑ sweat if all other factors are equal e.g., body SA)
• Excessive sweating leads to a loss of body fluids and when the level of fluid drops, the body’s core temp↑.
• It is this gradual dehydration that leads to heat exhaustion and heatstroke
• Sweat loss can reach 6-10% of body mass
• >2% generally means performance and thermoregulation are compromised!

Question 13

What is the body’s preferred mechanism of heat loss dependent on?

Answer 13

1. Environment: •Ambient temperature – if above the body’s core temperature, then evaporation is the only method of heat loss. Other methods will result in heat gain.•Forced convection – heat loss via convection will occur if it is windy.•Barriers to convection – clothing will minimise the effect of convection as it will insulate the boundary layer of air.•Temperature radiating surfaces – light clothing will not absorb as much heat as dark clothing•Relative humidity – if 100%, no heat loss via evaporation.
2. Age: •Children don’t sweat as much as their sweat glands are not as developed as adults
3. Physiological state: •Rate of heat production (how much work the athlete is performing)•Hydration state – will determine rate of evaporation as a reduction in plasma volume leads to a decrease in sweat rate

Question 14

What is Heart Rate (HR)?

Answer 14

The number of times the heart beats per minute.

Question 15

What is Stroke Volume (SV)?

Answer 15

The amount of blood ejected from the heart each beat.

Question 16

What is Cardiac Output (Q)?

Answer 16

The amount of blood circulating around the body every minute = HR*SV

Question 17

What is Double Heat load?

Answer 17

Situation where the body is forced to deal with 2 forms of heat (metabolic heat and environmental heat).

Question 18

What is Cardiovascular Drift (cardiac drift)

Answer 18

When heart rate increases to maintain cardiac output caused by a decrease in stroke volume.

Question 19

What is dehydration?

Answer 19

Occurs when the amount of water leaving the body is greater than the amount being taken in.

Question 20

We lose water by;

Answer 20

1. Breathing, as humidified air leaves the body.
2. Sweating, which is used as a cooling mechanism.
3. Urination or bowel movements in the removal of waste.

Question 21

Why do heart rate and cardiac output increase at rest in the heat?

Answer 21

• This is to allow more blood to be sent to the peripheries resulting in increased radiative heat loss to the environment, particularly from the hands, feet and forehead.
• When exercising in the heat, the body is forced to deal with 2 forms of heat, known as a double heat load
• Metabolic heat created by working muscle environmental heat in hot conditions

Question 22

As a result this double heat load creates competition for blood flow

Answer 22

1. Muscles and vital organs require blood flow to sustain energy metabolism
2. Skin blood flow is required to transport heat out to the environment to keep the core temperature cool. This blood flow cannot deliver its oxygen to the working muscles, impacting on performance.

Question 23

When exercising in the heat…

Answer 23

• , the body directs blood flow to the skin and away from the working muscles to increase heat loss via evaporation
• An ↑ in sweat rate → ↓ blood plasma volume.
• As a result, Cardiovascular Drift occurs;
• To maintain cardiac output, HR increases.
• This increase in HR is relatively smaller than the decrease in SV, therefore cardiac output is reduced.
• As a result, skin blood flow ↓ (a cooling mechanism) and oxygen sent to working muscles are also reduced, placing extra strain on the body to maintain exercise levels.
• A reduction in blood flow to the working muscles increases the production of lactic acid
• A reduction in blood flow to the skin reduces the rate of sweating, inhibiting the body’s ability to lose heat via evaporation. These changes lead to a rise in core temperature and negatively affect performance