L33 Exercise and Thermal Stress

Question 1

Precisely define core temperature

Answer 1

Temp of the hypothalamus, the thermoregulatory centre of the body . Area of the body where temperature is constant as heat dissipation changes

Question 2

List the available methods for measuring core temperature and describe their relative strengths and weaknesses

Answer 2

Oral temperature - temperature change is regular due to food intake and fluid. but is easy to measure

Rectal temperature - most accurate for measuring core temperature. Issues of privacy. Faeces can generate inaccurate readings

Tympanic temperature - senses reflected infrared emissions from the tympanic membrane through a probe places in the auditory canal. It is quick, minimally invasive, easy to perform. Temperature can be warmer if the person has been lying on their ear. Earwax can also obscure results

Stomach temperature - swallowed telemetry pill

Question 3

Describe the four mechanisms of heat transfer

Answer 3

1. CONDUCTION
   - transfer of heat down a thermal gradient via direct contract between objects. Important within cells (cell to capillary wall). Only 3% of heat loss at normal room temperature
2. CONVECTION
   - Transfer if heat between object and moving fluid or air. 12% of heat loss @ room temp. Blood is main mover of heat within the body.
   - Rate of heat transfer depends on: temp gradient, thermal conductivity, surface area, velocity of fluid. Water conducts heat 25 times faster than air
3. RADIATION
   - Loss or gain of heat in the form of electromagnetic waves. 60% of heat loss @ room temp.
   - Rate of radiant heat transfer depends on: Temp gradient, area of mutually exposed surface, colour + reflectivity. Sun is major source of radiant heat
4. EVAPORATION
   - 25% of heat loss @ room temperature. Evaporation only means of cooling as high environmental temperatures. Sweat only effective fir cooling if it evaporates.
   - Rate of evaporative heat transfer depends on: surface area exposed to environment, tem and relatively humidity of ambient air, convective air currents

Question 4

Explain how ambient temperature influences heat exchange via evaporation, convection and radiation

Answer 4

Evaporation
- 25% of heat loss @ room temperature

Convection
- 12% of heat loss @ room temp.

Radiation
- 60% of heat loss @ room temp.

Question 5

Explain how relative humidity influences potential heat loss via evaporation and the consequences to sweat rate and core temperature

Answer 5

Sweat rate increases during time of exercise
Core temperature increases as exercise time increases
These values are both a lot higher than a cool environment.

Question 6

Explain how the hypothalamus maintains thermal balance

Answer 6

Temp regulation centre located in the hypothalamus. Thermoreceptors in skin and brain (hypothalamus).
Physiological thermoregulatory processes initiated.

Thermoreceptors detect the changes, which is sent to the hypothalamus which then signals the effectors to make a change eg sweat glands, skin vasodilation/constriction

Question 7

What are the factors that affect heat injury and how?

Answer 7

Acclimatization
- exercise in heat for 10-14 days - lower body temp and HR response. Best protection against heat stroke

Fitness
- Higher fitness related to lower risk of heat injury - tolerate more work in the heat, acclimatize faster, sweat more

Clothing
- Expose as much skin as possible. Choose materials that wick sweat away

Hydration
- Inadequate hydration increases risk of heat injury. No differences among water, electrolyte drinks or carbohydrate-electrolyte drinks

Metabolic rate
- Core temp is proportional to work rate

Wind
-Wind will increase heat loss by convection and evaporation

Environmental temp
- convection and radiation dependent on gradient between skin and air temp. High temperature may results in heat gain.

Environmental humidity
- Evaporation id dependent on gradient between skin and air . Relative humidity is a good index of water vapour pressure.