extreme biology lecture 6 - humans (temperature) Flashcards
what is the goal that body heat should be to maintain balance?
Protected human can tolerate environmental temperatures ranging from -50◦C to 100 ◦C
Goal is to maintain core temperature
Thermal comfort:
- Core temperature between 36.6 and 37.1 ◦C
- Skin Temperature between 32 and 35.5 ◦C
how do you monitor heat balance?
Diurnal fluctuations: lowest in sleep
Person can tolerate (just) a drop of 10˚C in core temperature, but only a 5 ˚C rise.
Measurements:
Oral temperature averages ~0.56 ˚C less than core temperature.
Oral measures does not reflect deep core temp
what is the role the hypothalamus?
-Located at the base of the brain above the pituitary glands (approx. the size of a pea!).
-Major role is to keep the body in homeostasis
-Responds to signals from internal and external environment:
e.g. temperature, hormone levels in the circulation, satiety, blood pressure.
-Serves as a thermostat: Regulates core temperature to 37 ± 1˚C
what does the hypothalamus do?
The hypothalamus initiates responses to protect the body when core temperature changes.
Heat regulating mechanisms are activated by:
1) Thermal receptors in the skin provide information about surface temperature of the body.
2) Temperature changes in blood perfusing the hypothalamus
how should you dress in the cold?
-Fibres in clothing traps air and warms it (creates barrier to heat loss)
-Thicker zone of trapped air next to skin provides better insulation
-Several layers traps air better (or thick clothing lined with fur/feathers/synthetic fibres)
-Be windproof
-Wick moisture away from body (to then evaporate)
what is exercising like in the cold?
Low intensity exercise
Walking at ~5km/hr at 5˚C (in winter clothing) in dry and wet conditions
Clothing (an “unprepared” hiker)
Cotton t-shirt
Long-sleeved t-shirt
Thin non-waterproof windbreaker
Jeans
Leather boots
All clothing saturated within 15min of rain starting.
Wet conditions:
Initial rise in core temp (peripheral vasoconstriction, shunting of blood to core)
N.B. 18 subjects recruited, only 5 completed rain protocol
what are cold injuries?
Begins at ambient temp of ~ -12˚C & wind speed >5mph
Frostbite (freezing of tissue & formation of ice crystals)
1st degree: damage to superficial layer of the skin.
2nd degree: blisters on the skin
3rd degree: freezing of deeper tissue (subcutaneous & muscle)
Treatment:
1st: simple re-warming
2nd: leave the blisters
3rd: hospitalisation (can result in amputation of effected area)
what are the 3 reasons that the Cold effects us?
1) Action potentials
- At a tissue temperature of ~20˚C, conduction velocity, amplitude and repolarisation of action potentials is slowed.
2) Power output (in the muscle)
- Max power output drops by ~3% per ˚C reduction in muscle temp.
- Incapacitation can occur at a muscle temp of ~27˚C
- Castellani & Tipton (2015) Handbook of Physiology, Environmental Physiology
3) VO2max : reduced by 10-30% if core temp falls by 0.5-2˚C
- in exercise, stride frequency can increase/stride length decrease leading to slips and falls.
what are the primary acclimatisation adaptations?
-9 consecutive days of heat exposure
-100 min per exposure
-Intensity: 300 kcal/hr
-Temp: 48.9˚C
Outcome:
- Increased sweat rate
- reduced core temp
- reduced HR
what are the correct conditions for exercise in Vienna?
Environmental conditions for Vienna:
Temp: min 6.4˚C, max 14.3˚C
Humidity: 79%
Wind speed: 9.1 km/h
what is meant by optimal temperature for optimal performance case study?
Current Men’s Marathon World Record
Holder: Kelvin Kiptum
Time: 2:00:35
When: 8th October 2023
Location: Chicago (flat course)
Conditions: ~13˚C
Previous Men’s Marathon World Record
Holder: Eliud Kipchoge
Time: 2:01:09
When: 25th September 2022
Location: Berlin (flat course, fewer turns)
Conditions: ~11˚C
N.B.: Last 8 world records were at Berlin
What are the types of responses to the cold?
-vascular
-muscle activity
-hormonal
what is the recommendations for football in hot environments?
-perform pre-participation screenings before competition in the heat
-watch at risk individuals and observe signs and symptoms if WBGT > 28oC
-add additional fluid breaks and force medical coverage if WBGT > 30oC
-reconsider event if WGBT > 32oC
what are strategies to deal with the cold?
Heat acclimatisation = physiological changes that improve heat tolerance
The goal:
-to reduce core temperature when exercising in the heat
-increase rate of heat loss (i.e. increase sweat rate)
