Mitigating The Negative Impacts Of Heat Stress

Question 1

What is heat acclimation?

Answer 1

Is a transient phenomenon

Adaptations will gradually recede if the heat stimulus is not maintained. This is called decay

Question 2

What is heat acclimation decay?

Answer 2

Heat acclimation decay is not as rapid as its induction.

Some degree of decay is often observed by ~14 days from the final heat exposure.

Question 3

How long can some adaptations like heart rate and core body temperature reductions be retained?

Answer 3

Some adaptations (i.e. heart rate and core body temperature reductions) can be retained (albeit partially) for up to about a month.

Daar

Question 4

What is required for heat acclimation?

Answer 4

Repeat heat exposures

Heat acclimation requires repeat heat exposures

Question 5

How can heat acclimation be achieved?

Answer 5

Passively or over a short period (e.g., 5 days)

This can be achieved passively or over a short period (e.g., 5 days)

Question 6

What is the decay rate of heat adaptations?

Answer 6

Slower than its induction

The decay of heat adaptations appears to be slower than its induction

Question 7

When can heat acclimation be performed in advance?

Answer 7

Before competition

Thus, heat acclimation can be performed in advance of competition and supplemented by a short ‘top-up’ prior to competition

Question 8

What does a second acclimation period allow for?

Answer 8

Faster and more profound adaptations

A second acclimation period allows for faster and in some cases more profound adaptations

Question 9

What does endurance performance rely on?

Answer 9

Ability to evaporate & replace fluids

Evaporating 1 g H2O removes 2.43 kJ heat.

Question 10

What are eccrine sweat glands known for?

Answer 10

Humans unique in their ability to sweat

• 2.5-4 million glands
• Virtually entire surface
• High output: up to 1.5-3.7 Lhr-1

Question 11

What is the maximum gastric emptying rate?

Answer 11

1 - 1.2 L-hr

Sweat causes dehydration. Dehydration common during exercise in the heat, even if drinking at max rate that GI can handle (which is rare).

Question 12

What does low body water impair?

Answer 12

Cardiovascular function, Sweat production, Cognition, Amount of internal heat sink

Hydration and heat tolerance

Question 13

What can wipe out benefits of improved fitness or acclimation?

Answer 13

Hyponatraemia

Can wipe out benefits of improved fitness or acclimation.

Question 14

What is Dehydration (% body weight loss)?

Answer 14

Dehydration (% body weight loss)

Delesdration

Question 15

What are some symptoms of heat syncopes?

Answer 15

Hit teen forene, (Heat) syncopes, Heat examst

Heat syncopes

Question 16

What is a potential risk of low body water and heat?

Answer 16

Heat stroke

Heal stroke?

Question 17

What is the book referenced for extreme physiology and medicine?

Answer 17

Cotter (2014) Extreme physiology and medicine

Cotter (2014) Extreme physiology and medicine

Question 18

How is hydration status typically measured in the lab?

Answer 18

Urine osmolarity, density or specific gravity

+ves: cheap, non-invasive, easy to measure
-ves: only detects large changes in fluid balance, lags behind blood plasma osmolality

Question 19

What are the challenges in accurately determining hydration status from single samples?

Answer 19

Hydration status is difficult to accurately determine from single samples, & thresholds between euhydration and hypohydration difficult to establish

Question 20

What are the methods for measuring hydration status that can accurately measure acute changes?

Answer 20

Haemoglobin concentration, blood osmolality

+ves: accurately measures acute changes in hydration status.
-ves: invasive, relatively expensive, requires specialised training, requires appropriate sample storage

Question 21

How are changes in body mass typically measured?

Answer 21

Changes in body mass

+ves: cheap, reliable, no technical skills required to measure
-ves: measurement can be difficult e.g., requires accurate scales on flat ground, nude body mass is best, food and fluid ingestion may need to be recorded

Question 22

What criteria indicate an individual is euhydrated?

Answer 22

daily body mass changes remain <1%
plasma osmolality is <290 mmol/kg
urine specific gravity is <1.020

An individual is considered euhydrated if these criteria are met.

Question 23

What is the best method for measuring body mass changes?

Answer 23

Measuring post-void nude body mass in the morning, on consecutive days after consuming 1-2L of fluid the prior evening

Establishing baseline body mass is essential.

Question 24

What is the least sensitive marker for hydration status?

Answer 24

Urine colour

Urine colour can be useful when measured in conjunction with other markers.

Question 25

Can urine be personalized?

Answer 25

Yes

Urine can be personalized.

Question 26

What are examples of internal cooling techniques?

Answer 26

Ice slurries, drinking cool water

Internal cooling techniques include ice slurries, drinking cool water to reduce thermal strain due to lowering core body temperature and creating a heat sink.

Question 27

What is the mechanism of action for internal cooling?

Answer 27

Larger heat sink means a lower internal body temperature

Cold/iced beverages stimulate thermoreceptors in the mouth and gut, improving thermal comfort and thermal sensation during exercise heat stress. Help maintain hydration status.

Question 28

What are some disadvantages/considerations of internal cooling?

Answer 28

Skin temperature affected following internal cooling strategy. Brain freeze, gastro-intestinal distress etc. Potentially unhelpful artificial lowering of internal body temp, affecting thermoeffector responses (e.g., inhibit sweating response inappropriately). Cooling strategies need to be practiced during training.

20 10

Question 29

What are some examples of external cooling techniques?

Answer 29

External cooling techniques include cooling garments, cold water immersion, or fanning.

Example: Cooling garments, cold water immersion, fanning

Question 30

What is the aim of external cooling?

Answer 30

The aim of external cooling is to reduce thermal strain via an increase in the core-to-skin temperature gradient and an improved thermal perception.

Mechanisms: Increase core-to-skin temperature gradient, improved thermal perception

Question 31

What is the mechanism of action for external cooling?

Answer 31

The mechanism of action for external cooling involves lowering of skin temperature, which increases the core-to-skin temperature gradient.

Implications: Lower mean skin temp allows better maintenance of central blood volume, reduces cardiovascular strain, improves aerobic performance

Question 32

What are some disadvantages/considerations of external cooling?

Answer 32

Some disadvantages/considerations of external cooling include the importance of body surface area, fit of a garment for maximum heat transfer, cooling capacity, and duration (suggested 20 min).

Details: Larger body surface area is better, fit of garment important, duration suggestions

Question 33

What is the effect of cooling on performance?

Answer 33

Cooling improves performance in hot conditions.

Question 34

Who benefits most from cooling?

Answer 34

Endurance athletes seem to benefit most from cooling. Athletes undergoing the largest heat gain during performance stand to benefit the most from cooling.

Question 35

Do power athletes benefit from cooling?

Answer 35

Power athletes (e.g., sprinters, jumpers) do not benefit from cooling, and exercise performance may even be impaired following precooling.

Question 36

How may cooling strategies affect performance?

Answer 36

Cooling strategies may affect working muscle temperatures and thus impair skeletal muscle contractility and anaerobic metabolism.

Question 37

During self-paced exercise how is work rate regulated?

Answer 37

Previously proposed that the brain regulates the degree of muscle activation and thus, exercise intensity specifically to prevent harm.

e.g., muscle, lungs, heart….

Question 38

What is proposed to regulate work rate during self-paced exercise?

Answer 38

A combination of feedback from various systems regulate work rate during self-paced exercise.

e.g., muscle, lungs, heart….