Exam 3 Flashcards
normal core body temp
37* C
above 45* C core body temp
may destroy proteins and enzymes and lead to death
below 34*C core body temp
may cause slowed metabolism and arrhythmias
thermal gradient from body core to skin surface
- ideal gradient is 4* C
- in extreme cold, may be up to 20*
Voluntary Heat Production
Exercise
70-80% energy expenditure appears as heat
Involuntary heat production
shivering- increases heat production by 5x
non-shivering thermogenesis- action of hormones thyroxine, catecholamines (speed up metabolism)
Radiation
- transfer of heat via infrared rays
- 60% heat loss at rest
- can be method of heat gain
Conduction
heat loss due to contact with another surface
Convection
- heat transferred to air or water
- ex: fan pushing air past skin
Evaporation
-heat from skin converts water to water vapor
Evaporation rate depends on:
- temperature and relative humidity
- convective currents around the body
- amount of skin surface exposed
skin vapor pressure
~32 mmHg
(the greater the gradient or difference is the greater heat loss)
% heat loss at rest due to evaporation
25%
L of sweat evaporated to kcal heat lost
1 L (1000 ml) sweat results in heat loss of 580 kcal
(body loses 0.58 kcal heat/ml sweat evaporated)
Calculation of heat loss via evaporation
- total energy expenditure (min * kcal/min)
- total heat produced
(kcal * energy lost as heat) - evaporation to prevent heat gain
(kcal / kcal/L)
Heat produced that is not lost…
is stored in body tissues and will raise body temperature
body heat gain during exercise
heat produced - heat loss
amount of heat required to raise body temperature
specific heat of human body is 0.83 kcal/kg
(heat required to raise body tem 1* C = specific heat * body mass)
Calculation of body temp increase during exercise
- total energy expenditure (min *Kcal/min)
- total heat produced
- total heat stored
- amount of heat storage to increase body temperature by 1*C
- increase in body temperature during exercise
- post-exercise body temperature
Preoptic anterior hypothalamus (POAH)
- body’s “thermostat”, maintains around constant core temperature
POAH response to increase in core temp
- cutaneous vasodilation, allowing increased heat loss
- stimulation of sweat glands for evaporative heat loss
response to decrease in core temperature
- shivering and increased norepinephrine release
- decreased skin blood flow via vasoconstriction
as temperature and humidity goes up…
the body relies on evaporative heat loss more as convective and radiative heat loss become methods for heat gain
Heat Index
relative humidity added to air temperature, measure of how hot it feels
high relative humidity reduces evaporated heat loss
- lowers heat loss
- increases body temperature
exercise in the heat
- reduced ability to lose body heat
- higher sweat rate, may be as high as 4-5 L/hour, risk of dehydration
dehydration and performance
dehydration of 1-2% body weight can impair performance
hydration guidelines
- hydrate prior to performance
- consume 150-300 ml fluid every 15-20 min
- monitor urine color
impaired exercise performance in hot environment
- cardiovascular dysfunction: reduced stroke volume, cardiac output, and muscle blood flow
- accelerated muscle fatigue: increased radical production, decreased muscle pH, muscle glycogen depletion
-central nervous system dysfunction: decreased motivation, reduced voluntary activation of motor units
gender and age heat acclimitization
no difference
Precooling
lowering body temp before exercise in the heat improves exercise performance
combining cooling techniques increases imporvement
acclimation
rapid adaptation (days to weeks) to environmnetal change
acclimatization
adaptation over a long time period (weeks to months)
acclimation and inactivity
acclimation is lost within days of inactivity or no heat exposure
significant decline in 7 days, complete loss in 28 days
physiological adaptations during heat acclimation (4)
- 10-12% increase in plasma volume to maintain blood volume, stroke volume, and sweating capacity
- earlier onset of sweating and higher sweat rate
- reduced skin blood flow
- reduced sodium chloride loss in sweat, reduced risk of electrolyte disturbance
Heat acclimation and heat shock proteins
-heat acclimation reduces the risk of heat injury in response to exposure of heat stress
- protection is due to synthesis of heat shock proteins in cells, protect cells from thermal injury, stabilizing and refolding damaged proteins
exercise in vinyl suits
- can promote acclimation
- risk of hyperthermia
- not effective for weight loss
exercise in cool for heat acclimation
it works but less than training in the heat
partial pressure
- % of O2, CO2, and N2 in the air is same
- there is lower partial pressure of O2, CO2, and N2 at higher altitudes
atmospheric pressure
decreases at higher altitude
hypoxia
low partial pressure of O2 (at altitude)
Normoxia
normal PO2 (sea level)
Hyperoxia
high PO2 (below sea level)
Altitude and short term anaerobic performance
- lower PO2 has no effect on performance
- lower air resistance may improve performance
altitude and long term aerobic performance
- lower PO2 results in poorer aerobic performance as it is dependent on oxygen delivery to muscle
altitude and VO2 max
- decreased VO2 max at higher altitude due to lower oxygen extraction
- decreased maximal cardiac output at altitude
moderate altitude and VO2 max
decreased VO2 max due to decreased arterial PO2
