A2 PE

Thermoregulation

Learning Outcomes• Define thermoregulation and the

body’s four methods of thermoregulation.

• Explain the importance of the body maintaining its temperature.

Thermoregulation• What will the man below be experiencing?

Thermoregulation

• As with anything the body is affected by the heat of the environment and anything else surrounding it.

• The body is able to adjust its own temperature constantly to keep it in a safe zone.

• This is called being homeothermic.

Thermoregulation• Body temp fluctuates

from hour to hour by roughly 1.0°C.

• The normal zone for the body is 36.1°-37.8°C.

• Only extreme cold, heat, illness or exercise takes the body out of this ‘safe zone’.

HEAT GAIN HEAT LOSS

METABOLIC HEAT

ENVIRONMENTAL HEAT/SOLAR RADIATION

RADIATION

CONDUCTION

CONVECTION

EVAPORATION

THE SCALES OF BODY TEMPERATURE

SHIVERING

EXERCISE

Convection

• As the air is constantly moving around us, the colder molecules in the air ‘sweep away’ the warm molecules next to our skin.

• This also occurs when the skin is submerged in water.

• Conduction and Convection together will account for 10-20% of heat loss.

• This is 26 times more when you’re in water.

Conduction• Conduction is the passing of heat from

one tissue into another it is in contact with.

• For example, from the muscle to the skin, from the skin to your clothes or the air.

• If the air next to the skin is warm as well, then less of the heat can be conducted from the skin.

Radiation• The body is constantly giving off heat in the

form of infrared rays. • At normal room temperature, the nude body

will lose 60% of it’s natural heat in this manner.

• The body gains the most heat in the same way. If the environment is warmer than your skin, your body absorbs the heat.

• If the environment is much colder, the body loses heat much quicker.

Radiation

Evaporation

• What happens when you start running?

Evaporation• The body moves water

to the surface of the skin where it can evaporate and carry the heat off the body.

• At rest – 20%• Active – 80%• If the water doesn’t

evaporate, very little heat is lost and most is reabsorbed.

• Don’t remove sweat with a towel!

Humidity

• Which of the four methods of thermoregulation allows the most heat to be removed from the body?

• Evaporation.• The more water molecules that are

already in the air, the less moisture can evaporate.

Humidity

• Where are you likely to feel the most sweaty??

• The Dubai or Singapore?• 2 minutes

Humidity

• The dry hot air of Dubai would allow the sweat to evaporate almost immediately, whereas the moist air of the Singapore would not allow much heat to be lost through evaporation, causing the body to continue sweating.

• What problems could both of these situations cause?

Thermoregulation in Sport

• The harder the muscles are working, the more heat is generated.

• The more energy that is being processed by the body the more heat is being generated.

• If the environment is warmer than the body, no heat can be removed from the body.

• Think Vasodilation/constriction

Thermoregulation in Sport

• At the same time, if the environment is too cold, then heat will be lost too quickly.

• Due to increased or decreased temperature effects the flow of blood, the contractions of all the muscles (including the heart) and the functions of the nervous system.

• Clothing will play a large role in this, as we’ll see in our experiment next session!

Key terms• Hyperthermia – a condition in which

body temperature is elevated to a very high level

• Hypothermia – a condition in which body temperature is lowered to a very low level

• Hypohydration – a condition in which there are very low levels of fluid in the body

Surface Area to mass ratio

• Small children lose temp quicker than large people

• Gymnasts, distance runners, jockeys• V• Weight lifters, sumo wrestling,

throwers, rugby players

What happens in the body?

• Thermoregulatory centre is situated in the hypothalamus – in the brain

• Receives signals from central and peripheral receptors

• But what can the body do…..

Reactions...in addition to sweat

• Vasoconstriction/dilation• Exercise in warm climate

– Cardiac output shared between muscles & skin– Can cause a reduction in cardiac return and as

a consequence SV – effects performance• Increase in heart rate (Cardiac drift) – but

has a limited effect on performance

•

Effect of temp

• Ability to run/cycle for long periods reduces as temperature increases 11oC to 21oC to 31oC

• Dehydration – big risk at warm and cold temps (lost through respiratory system but also sweat if wearing thick clothing) – leads to fatigue

• Fluid intake essential - hypohydration

Effects of Differing Body Temperature• 37°C – Normal Temp.• 39°C – Severe sweating, fast heart rate

and breathlessness• 41°C – Fainting, vomiting,

hallucinations• 43°C – Possible death, serious brain

damage.• 44°C – Almost certain death

Effects of Differing Body Temperature• 36°C – Moderate shivering – sleep

temp.• 34°C – Hypothermia• 32°C – Hallucinations, extreme

sleepiness and comatose• 27°C – Approaching death• 25°C – Death due to irregular heart rate

But........

• You do need to be warmer than normal during sport for the following advantages......

V02

MA

X

Exercise Time

Hea

rt R

ate

Exercise Time

HOT

COLD

Effects of Heat Increase

• Higher V02 MAX• Higher heart rate and quicker increase

of heart rate• But• Increased blood lactate and quicker

build of lactate.

Task

• Alan is a long distance runner who is used to training in Berkshire. He is taking part in a race in the south of Spain in July.

• Explain what will be happening to his body during the race due to his body’s activity, the environment and the type of clothing he’ll be wearing.

• 10 minutes

Next Session

• Bring your kit, we’ll be in the gym.• And you will probably need shower

stuff!

Learning Outcomes• Define and discuss the different types

of body composition methods.• Explain who these methods would be

useful for.