Heat Acclimation Flashcards
Define acclimation
- acclimation: physiological or behavioral adaptive changes in response experimentally induced changes of a particular climatic factors such as temperature and humidity in a controlled environment
Define acclimatization
Physiological or behavioral adaptive changes that occur within an organism to reduce strain caused by stressful changes in the natural climate
How long does it take to complete heat acclimation
10-14 days
75-80% in the first 5-7 days
What type of exercise will induce heat acclimation
- exercise at 50-75% VO2max for 60 min/day
What occurs in the acute phase of acclimation
- Decrease eccrine sweating
- Increase core and skin temperature
- tachycardia, decreased stroke volumes
- Decreased thermal comfort
- increases borg rating of perceived exertion
- Decreased exercise tolerance
- Increase electrolyte loss in urine/sweat
What occurs in the chronic phase
- reversal or improvement of acute phase variables: Sweating, Tc, HR plateau
- increased plasma volume
- Decreased electrolyte loss in sweat/urine
- Increased thermal comfort/decreased BPRE
- Increased exercise tolerance
What occurs acutely in regards to the cardiorespiratory system & acclimation
- decreased stroke volume; due to decreased VR
- increased heart rate (to increase CO)
- Decreased liver/splanchnic BF
- Increased skin BF
what is hypothesized to happen with wet heat vs dry heat acclimation
- wet/dry: Increased stroke vol
- Dry: improved cardiac output
What happens to sweating and skin blood flow when comparing acclimated and non-acclimated individuals
- acclimated individuals sweat/increase skin blood flow at a lower core temperature for a given heat exposure when compared to non-acclimated individuals
- sweat distribution changes from trunk to limbs improving evaporation and surface cooling
What happens to the composition of sweat in heat acclimated individuals
- decreased Na in sweat of acclimated individuals (but increased sweat rate)
What are two methods which total body water might increase with heat acclimation
- increased ICF or increased ECF can cause an increase in total body water by 5-7% however this is quite variable
- depends on duration of heat exposure, exercise…
What mechanisms are involved in ECF/Plasma vol increase
- Na+ and H2O retention
- net fluid shift from interstitium to plasma due to increased oncotic pressure
- warm skin gives venodilation lowering post capillary resistance and mediates net fluid reabsorption into plasma, as well as hemodilution
What hormonal changes are initially expected during heat acclimation
- ACTH increases due to circulatory strain early in HA
- This results in an increase in plasma aldosterone and cortisol
- Aldosterone is also increased via the renin-angiotensin system
- These hormones then act on the distal convoluted tubule and the collecting duct to increase the retention of Na+ within a few hours
- They also act on the sweat glands to increase Na+ retention within a few days (some debate if Ald. does this alone)
What hormonal changes are expected a few days after heat acclimation
- The Na+ conserving effects of aldosterone causes ACTH levels to drop
How does one’s fitness level affect their time to heat acclimate
- the more fit someone is (i.e greater VO2) the less time it takes for them to HA
