W7 - Hot/Humid Environments Flashcards
How important might ambient temperature be to endurance performance?
Very.
Many studies show athletes in a hot env can do less exercise compared to in a cooler env.
If exercise is occurring at a higher temp then athletes will tire quicker + it will -ively impact performance.
Temperature for normothermia
36.5-37.5 degrees celcius
What is hyperthermia
1 degree Celsius increase in our normal core temp.
What is the most important mechanism of heat loss during exercise?
Evaporation
When does sweating only cool you down?
When it evaporates off the skin.
What must be homeostatic ally controlled?
Core temp
When is core temp its highest?
Afternoon
Literature link to oeseophageal temp
Despite different oesophageal temperatures at the start, all participants reached exhaustion at oesophageal temperatures 40.1-40.2 celsius
(Gonazles-Alonzo et al, 1999)
What has been revealed to be the optimum temp for endurance performance until exhaustion and by who?
11 degrees celcius
Galloway & Maughan 1997
What has been revealed to be the optimum temp for endurance performance for those who are the top 25% in their fields until exhaustion and by who?
women - 10.
men - 7.
Helou et al, 2012
Data for the finishers of the Olympic marathon from 1896-2000
<25 celsius = 79% of runners finished
> 25 celsius = 54% of runners finished
Are sweat losses usually a limiting factor during exercise?
NO
Sweat losses of ~2 and ~3 %
~2% bodyweight can impair prolonged endurance performance.
~3% may elicit impairments in cognitive function.
What does passive raising of core temp reduce?
Voluntary activation
What is associated to drowsiness?
Increase in alpha and beta brainwaves.
When is global cerebral oxygenation likely to be impaired?
When CBF is reduced beyond 50%
What has a dependent effect of. muscle temp on peak power output?
Velocity
Improving performance in the heat…
Effective interventions can be carried out in the days before (chronic) or on the day of + during (acute) heat exposure + 1 will achieve 1 or + of the following…
Increased or maintained heat dissipation
Reduced initial body heat
Altered thermal perception.
Acclimation vs acclimatisation
Acclimation - Laboratory
Acclimatisation - Natural env.
What has reduced initial deep-body temp + increased heat dissipation rates?
Acclimation and/or acclimatisation to heat
What is the benefit to acclimation or acclimatisation to the heat?
Reduces thermal-strain for a given external work-rate during exercise in a thermally stressful env.
How is heat acclimatisation/acclimation achieved?
By repeatedly elevating deep-body and skin temp to a high level that elicits pronounced sweating.
Active approaches of acclimatisation/acclimation
Exercise in a hot+/or humid env
Exercise in clothing restricting heat loss.
Passive approaches of acclimatisation/acclimation
Hot baths can be effective
Which are more effective for acclimatisaiton/acclimation?
Longer or shorter exposures?
Longer i.e ~10 daily exposures rather than ~5
Sex differences for the rates of acclimatisation/acclimation?
Adaptation may be slower in females
Acclimation/Acclimatisation
What is a common target temperature for the deep-body to reach?
~38.5
Higher temps could increase heat-illness risk.
How long is heat acclimation/acclimatisation retained for?
At least 7 days
Any benefits that are lost within a month are re-acquired with 2-4 further exposures.
What comes under acute interventions
Hydration
Pre + per cooling
Perceptual manipulation
Strategy for the acute hydration intervention
Ensure euhydration prior to exercise
Prevent excessive dehydration thereafter.
Strengths to the acute hydration intervention
Helps maintain thermoregulatory capability
Cost-effective
Weaknesses to the acute hydration intervention
Practically/logistically difficult in some situations.
Palatability/tolerance may affect ingestion rate.
Strategy for the acute pre/per-cooling intervention
External i.e cool water immersion + cooling garments.
Internal i.e cool-liquid ingestion
Mixed-methdos
Strengths for the pre/per-cooling acute intervention
Reduced initial body heat content +/or creates heat sink.
Effective when evaporation is compromised
Cost-effective
Weaknesses for the pre/per-cooling acute intervention
Can be logistically difficult.
Deep-body temp monitoring required for pre-cooling.
Cooling garment efficacy influenced by env.
Strategy of acute perceptual manipulations
L-menthol application
Local cooling
Strengths to the acute perceptual manipulations intervention
Cost - effective
Reduced perception of hotness.
Weakness to the acute perceptual manipulations intervention
Little/no effect on thermal state.
Potentially dangerous as may enable high deep-body temps.
By how much does pre-cooling aim to reduce deep-body temp?
By ~0.5-1 degree
Enabling greater heat storage before hyperthermia develops.
What does decreased muscle and skin temp cause?
Cutaneous vasoconstriction
Diverts blood from active tissues + slows nerve conduction + muscle contraction with can cause initial feelings of ‘sluggishness’.
Exercise in the heat is associated with a thermoregulatory burden mediating what
CV challenges
Influencing cerebral function
Increases pulmonary ventilation
Alters muscle metabolism
What is performance clearly impaired by for max intensity exercise in the heat?
CV limitations to support both the thermoregulation and O2 delivery to the active skeletal muscle at the same time.
What does central fatigue during exercise in the heat appear to be influenced by?
NT activity of the dopaminergic system.
Define heat stress
Refers to the env exercise conditions that elevate body temp
Define heat strain
Refers to the physiological consequences of heat stress.
What is the magnitude of stress + the resulting strain dependent on the complex interaction of during exercise in the heat?
Env factors i.e ambient temp, humidity, clothing worn…
Ind biological characteristics i.e heat acclimatisation status, aerobic fitness + body size.
Exercise task i.e metabolic rate + duration
The greater the heat stress…
The greater the impaired aerobic exercise performance.
Heat acclimatisation moderates these performance impairments, dehydration accentuates them.
When will the core-to-skin temp gradient be narrower
In warm-hot env than cool-temp env.
Reductions in renal and gastrointestinal bf in combination with peripheral venonconstricition may benefit the….
Translocation of blood to the central circulation + help sustain cardiac filling during exercise-heat stress.
What may happen if gut perfusion is insufficient for a prolonged period during exercise in the heat?
It can act to impair aerobic perf by reducing water + substrate uptake from the gut + provoke endotoxin leakage.
What has endotoxin leakage been recognised to contribute to?
Heat stroke
When is impairment to aerobic exercise capacity due to increased heat stress present?
During moderate + high intensity exercise.
May emerge as lower power output or speed during TT or reduced TTE during exercise w/ a fixed workload.
What remains unclear surrounding dopamine levels and hyperthermia?
Remains unclear is low dopamine levels are involved in the central fatigue associated with hyperthermia.
What presents as a major challenge to the elite marathon runner?
Combination of high temp + high humidity.
Sweat evaporation limits the rise in core temp but dehydration will…
Impair CV function
= Fall in bf to muscle, skin + other tissues.
What is the rate of heat production in runners determined by?
Roughly proportional to running speed + body mass.
Also depends on ind running economy.
Where do faster runners perform at of their aerobic capacity?
Faster runners perform at a higher fraction of their aerobic capacity
(Maughan & Leiper, 1983)
