Module 8 Flashcards
Regular Body Temperature for human
range of 36.1 to 37.8 degrees celsius
usually 37 degrees celsius
Homeotherms
organisms that maintain constant temperature
what causes heat gain?
- BMR
- muscular activity
- hormones
- thermic effect of food
- postural changes
- environment
what causes heat loss
- radiation
- conduction
- convection
- evaporation
2 factors causing heat gain
- metabolism
- environment
conduction
- Temperature gradient between skin and surfaces (greater gradient = greater heat loss)
- Thermal qualities of surfaces (e.g. Water absorbing heat faster than air)
heat transfer via contact
Convection
- lost through air/gas
- wind cooling person off for instance
radiation
energy from fire radiating out to boil water (EMG waves)
evaporation
- water vapour from perspiration
- sweating (20% heat loss at rest)
- must evaporate for heat transfer
Heat loss at rest
%
60% through radiation and 40% through conduction, convection and evaporation
What temperature can cause brain death and death?
41 degrees brain death and 45 degrees guaranteed death
2 factors that activate hypothalamus
- input from thermal receptors in skin
- change in blood temperature
Process when body temp increases
- Body temperature exceeds 37 degrees
- Impulses sent to hypothalamus
- Vasodilation in skin where BVs cause heat loss through skin
- Sweat glands become more active increasing evaporate heat loss
- Decreased temperature
Metabolism impact on exercise
how much heat is generated compared to rest
15 fold increase of heat production
muscle -> core -> skin
Skin to Environment depends on
- temperature gradient (radiative and conductive heat loss)
- rate of evaporation
what happens if ambient temperature exceeds core temperature
conduction, convection and readiation cause heat gain
- therefore high ambient temperature = evaporation only effective means of heat loss
Heat Loss at Exercise
Intense = 80% evaporative sweat loss
- Higher SA = higher convection/evaporation
- Higher temperature = higher sweating
- Convection improves evaporation
- relative humidity of air (high RH impedes evaporation)
do not wipe off skin (only counts as heat loss once evaporated)
Relative Humidity (RH)
amount of water in ambient air compared to total quantity of moisture that air can hold
must be lower than moist skin for evaporation to occur
What happens to working muscles when blood is diverted to skin?
- less fuel (O2)
- greater dependance on anaerobic metabolism and accumulation of H+
- greater glycogen use
- Reduced ventilation
Impaired exercise and premature fatigue
During supine heat stress, skin can receive
7-8 L/min
Untrained person’s max Q
25 L/min
Cardiac Output during heat stress
15-25% of Q passes through skin (BVs near skin)
vasodilation = flushed appearance (increase in cutaneous blood flow)
Response to prolonged exercise in heat
Look at Frank Starling Curve
SV gradually decreases and HR gradually increases
blood flow redirected to skin and plasma volume decreases
decreased venous return, EDV, SV
How much sweat can be lost during intense exercise
3 L per hour (10-15% loss in BW in 2 hours)
Cardiovascular Drift (again!?)
lower SV and higher HR to maintain cardiac output
Minimise effects of heat (athletes)
- bench rotaiton
- cool rooms and spray players during breaks
- ice slushies and jackets
Heavy and Prolonged Exercise
- blood volume reduced via sweating
- Blood diverted away from periphery back to core and muscles (body unable to cool itself)
- Core temperature soars
Hyponatraemia
excess H2O intake during long events = drink salty drinks
Fluid replacement pre, during and post exercise
400-600 mL H2O 60 mins prior
150mL per 15-20 minutes
consume beyond thirst + drink salty drinks (sports drinks) to drive thirst
- 1 1/2x sweat loss
- sports drinks: replace electrolytes (Na+ and K+ as it is lost during exercise)
CHO intake post exercise
1st 2 hours post exercise for glycogen repletion
Heat Acclimitisastion
several days of activity in hot environment will lead to improved heat tolerance and performance
- increased in plasma volume
- decreased resting core temperature
- increased in sweat rate
- NACL content of sweat decrease
lasts for several weeks
