Thermoregulation & Exercise in Hot & Cold Flashcards
Homeothermic
body temp is constant
conduction
transfer of heat by direct molecular contact (such as body core to adjacent tissues, body surface to clothes or air)
convection
transfer of heat by the motion of a gas or liquid across a heated surface (air molecules, water molecules)
where is body temp regulated
thermoregulatory centre in hypothalamus
what is the normal body temp range
36.1-37.8 degrees celsius
4 methods of heat loss
evaporation
convection
conduction
radiation
which method of heat loss is occurring when more movement means more heat loss
convection
radiation
body heat is given off by in fared rays
what is the main source of heat loss at rest?
radiation
how much excess heat do you lose by radiation at room temp
60%
Evaporation
liquide (sweat) converted to a vapour by heat from the skin
what is the main method of heat transfer during exercise and how much heat is lost?
evaporation
80% at exercise and 20% at rest
which of the 4 heat loss methods can also make you gain heat
radiation
convection
conduction
what does sweat rate depend on?
environmental conditions, exercise intensity, fitness level,
acclimatization, hydration
what amount of sweating can happen at exercise?
1L/hr
what is the body’s mechanism to increase heat production through muscle activity
shivering
what happens with cold stress
peripheral blood flow decreases, blood flow to core increases
what are the catecholamines released to increase heat production during cold exposure
epinephrine
norepinephrine
what is the problem with exercising in the heat
skin and muscles competing for blood
This happens in what situation “ decreased venous return because decreased LVEDV and SV, maintained Q because increased HR and Cardiovascular drift occurs”?
exercise in the heat
why does earlier fatigue and exhaustion occur with exercise in the heat
increased rate of glycogen depletion and lactate accumulation
Euhydration
normal body water
Dehydration
loss of body water resulting in a state of hypohydration
hyperhydration
body retains excess body fluids
what is the risk of overheating when dehydrated?
impairment of thermoregulation
therefore decreased sweat rate, skin blood flow and SV function & exercise capacity
what is the max amount of water loss through sweating during exercise in the heat?
3L/hr
what is the main focus of fluid balance?
to maintain plasma volume
requirement for water depends on _____
weight
insensible perspiration
occurs on skin; non visible and mostly pure water and accounts for 30%
of body water losses
(always sweating)
Voluntary dehydration
loss of body water for a specific task/sport (decreased performance by 10-15%)
Involuntary Dehydration
hypo hydration of >2% of body weight leads to decreased performance. common in prolonged exercise events
What does fluid loss lead to?
reduction in CV function and temperature regulation, decreased plasma volume and decreased Q, increased core temp
what are 3 methods of preventing fluid loss
skin wetting
hyperhydration
rehydration
1lb = how many ml of dehydration after an exercise bout?
450ml
electrolyte replacement
sodium
potassium
what percent of volume ingested must be made to restore fluid volume
25-50% MORE than the loss
true or false: CHO is good for you after exercise
true, benefits exercise performance
what do glucose and electrolyte drinks help ?
maintain muscle / liver glycogen
blood glucose
post-exercise you should super hydrate with?
water,
electrolytes,
carbohydrates
4 environmental factors that lead to head stress
air temp
humidity
air velocity
amount of radiation
what does fitness level influence in heat stress
increased plasma volume, skin blood flow and sweating,
earlier sweating and more dilute
decreased heat stress
what does body comp influence in heat stress?
increased fat means increased heat stress and risk of heat stroke
what does hydration level influence in heat stress?
increased hydration means a decreased fluid loss but a similar SV
what does gender influence in heat stress
similar acclimatization but men sweat more and earlier at an increased rate
what does age influence in heat stress?
few differences but may have impeded heat dissipation because of impaired circulation
what does being a child mean for heat stress factors?
decreased Q and decreased blood available to the skin, decreased plasma volume, decreased sweating rate
Heat acclimatization
- within a week with 2-4 hours of daily exposure
- daily bouts of exercise in heat for 15-20 min
- improves ability to eliminate heat because of increased skin blood flow and increased sweat
- earlier sweating
- lower HR and core temp
- less blood needed at skin
- decreased reliance on CHO metabolism
Heat cramps
cramping of exercised muscles (spasm)
- due to decreased minerals and water
Heat exhaustion
CV system cannot meet demand because blood pools in periphery
symptoms of heat exhaustion
fatigue breathlessness hypotension dizziness fainting weak rapid pulse
Heat stroke
internal body temp greater than 40 C
stopping of sweating
rapid pulse and respiration
why does O2 consumption increase for a given intensity in the cold?
shivering takes energy
acclimatization to the cold
- > increase in blood flow to extremities to avoid cold stress on hands and feet
- > enhanced peripheral blood flow