Mitigating The Negative Impacts Of Heat Stress Flashcards
What is heat acclimation?
Is a transient phenomenon
Adaptations will gradually recede if the heat stimulus is not maintained. This is called decay
What is heat acclimation decay?
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.
How long can some adaptations like heart rate and core body temperature reductions be retained?
Some adaptations (i.e. heart rate and core body temperature reductions) can be retained (albeit partially) for up to about a month.
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What is required for heat acclimation?
Repeat heat exposures
Heat acclimation requires repeat heat exposures
How can heat acclimation be achieved?
Passively or over a short period (e.g., 5 days)
This can be achieved passively or over a short period (e.g., 5 days)
What is the decay rate of heat adaptations?
Slower than its induction
The decay of heat adaptations appears to be slower than its induction
When can heat acclimation be performed in advance?
Before competition
Thus, heat acclimation can be performed in advance of competition and supplemented by a short ‘top-up’ prior to competition
What does a second acclimation period allow for?
Faster and more profound adaptations
A second acclimation period allows for faster and in some cases more profound adaptations
What does endurance performance rely on?
Ability to evaporate & replace fluids
Evaporating 1 g H2O removes 2.43 kJ heat.
What are eccrine sweat glands known for?
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
What is the maximum gastric emptying rate?
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).
What does low body water impair?
Cardiovascular function, Sweat production, Cognition, Amount of internal heat sink
Hydration and heat tolerance
What can wipe out benefits of improved fitness or acclimation?
Hyponatraemia
Can wipe out benefits of improved fitness or acclimation.
What is Dehydration (% body weight loss)?
Dehydration (% body weight loss)
Delesdration
What are some symptoms of heat syncopes?
Hit teen forene, (Heat) syncopes, Heat examst
Heat syncopes
What is a potential risk of low body water and heat?
Heat stroke
Heal stroke?
What is the book referenced for extreme physiology and medicine?
Cotter (2014) Extreme physiology and medicine
Cotter (2014) Extreme physiology and medicine
How is hydration status typically measured in the lab?
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
What are the challenges in accurately determining hydration status from single samples?
Hydration status is difficult to accurately determine from single samples, & thresholds between euhydration and hypohydration difficult to establish
What are the methods for measuring hydration status that can accurately measure acute changes?
Haemoglobin concentration, blood osmolality
+ves: accurately measures acute changes in hydration status.
-ves: invasive, relatively expensive, requires specialised training, requires appropriate sample storage
How are changes in body mass typically measured?
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
What criteria indicate an individual is euhydrated?
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.
What is the best method for measuring body mass changes?
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.
What is the least sensitive marker for hydration status?
Urine colour
Urine colour can be useful when measured in conjunction with other markers.
Can urine be personalized?
Yes
Urine can be personalized.
What are examples of internal cooling techniques?
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.
What is the mechanism of action for internal cooling?
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.
What are some disadvantages/considerations of internal cooling?
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
What are some examples of external cooling techniques?
External cooling techniques include cooling garments, cold water immersion, or fanning.
Example: Cooling garments, cold water immersion, fanning
What is the aim of external cooling?
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
What is the mechanism of action for external cooling?
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
What are some disadvantages/considerations of external cooling?
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
What is the effect of cooling on performance?
Cooling improves performance in hot conditions.
Who benefits most from cooling?
Endurance athletes seem to benefit most from cooling. Athletes undergoing the largest heat gain during performance stand to benefit the most from cooling.
Do power athletes benefit from cooling?
Power athletes (e.g., sprinters, jumpers) do not benefit from cooling, and exercise performance may even be impaired following precooling.
How may cooling strategies affect performance?
Cooling strategies may affect working muscle temperatures and thus impair skeletal muscle contractility and anaerobic metabolism.
During self-paced exercise how is work rate regulated?
Previously proposed that the brain regulates the degree of muscle activation and thus, exercise intensity specifically to prevent harm.
e.g., muscle, lungs, heart….
What is proposed to regulate work rate during self-paced exercise?
A combination of feedback from various systems regulate work rate during self-paced exercise.
e.g., muscle, lungs, heart….
