Heat Acclimation

Question 1

Define acclimation

Answer 1

• 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

Question 2

Define acclimatization

Answer 2

Physiological or behavioral adaptive changes that occur within an organism to reduce strain caused by stressful changes in the natural climate

Question 3

How long does it take to complete heat acclimation

Answer 3

10-14 days

75-80% in the first 5-7 days

Question 4

What type of exercise will induce heat acclimation

Answer 4

• exercise at 50-75% VO2max for 60 min/day

Question 5

What occurs in the acute phase of acclimation

Answer 5

• 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

Question 6

What occurs in the chronic phase

Answer 6

• 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

Question 7

What occurs acutely in regards to the cardiorespiratory system & acclimation

Answer 7

• decreased stroke volume; due to decreased VR
• increased heart rate (to increase CO)
• Decreased liver/splanchnic BF
• Increased skin BF

Question 8

what is hypothesized to happen with wet heat vs dry heat acclimation

Answer 8

• wet/dry: Increased stroke vol

- Dry: improved cardiac output

Question 9

What happens to sweating and skin blood flow when comparing acclimated and non-acclimated individuals

Answer 9

• 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

Question 10

What happens to the composition of sweat in heat acclimated individuals

Answer 10

• decreased Na in sweat of acclimated individuals (but increased sweat rate)

Question 11

What are two methods which total body water might increase with heat acclimation

Answer 11

• 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…

Question 12

What mechanisms are involved in ECF/Plasma vol increase

Answer 12

• 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

Question 13

What hormonal changes are initially expected during heat acclimation

Answer 13

• 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)

Question 14

What hormonal changes are expected a few days after heat acclimation

Answer 14

• The Na+ conserving effects of aldosterone causes ACTH levels to drop

Question 15

How does one’s fitness level affect their time to heat acclimate

Answer 15

• the more fit someone is (i.e greater VO2) the less time it takes for them to HA

Question 16

What factors might one want to avoid if they’re wanting to maintain the benefits of HA

Answer 16

• sleep loss, infection, alcohol abuse
• salt depletion
• dehydration

Question 17

What is the formula for heat deacclimation

Answer 17

• %loss = (mean post acclimation value - mean acclimation value)/(mean unacclimation value-mean acclimation value)

Question 18

What is the general statement regarding deacclimation

Answer 18

• “one day out, loses 2 days of acclimation”

Question 19

does whether or not someone acclimatizes in a different season affect decay/reacclimation

Answer 19

• no there is no seasonal effects

Question 20

How does reacclimation affect one’s time to acclimate

Answer 20

• individuals who are reacclimating will acclimating faster than those acclimating for the first time

Question 21

What differences are there between HA DA and ReA for dehydration, RPE, thermal sensation, [lactate]

Answer 21

• No differences in dehydration, RPE, and [lactate].

- Difference in thermal sensation

Question 22

is decay greater in HA individuals who exercise or are passive

Answer 22

• exercise group

- higher decay in Tc, and HR