exercise in-the-heat-and-acclimatisation
TRANSCRIPT
APPLIED EXERCISE PHYSIOLOGY
-EXERCISE IN THE HEAT
Applied Exercise Physiology
On completion of this unit a learner should:1. Know how temperature and altitude affect
exercise and sports performance
2. Know about the physical differences between people of different gender and race and their affect on exercise and sports performance
3. Know the impact that the physiological effects of ageing have on exercise and sports performance
4. Know the effects and implications of using ergogenic aids for exercise and sports performance.
INTRODUCTION
EFFECT OF HIGH TEMPERATURES ON SPORT AND EXERCISE
You have evolved over millions of years to exist within a narrow range of Physiological variables
From the amount of water in your body, to the acidity in your cells and the concentration of glucose in your blood
These are regulated by physiological and hormonal responses to maintain “Optimal” conditions AKA?
Exercise and heat exsist to most adult as the biggest CHALLENGE to HOMEOSTASIS
Most sports have to compete in change of climate
This pushes bodies ability to control its internal environment, this has significant physiological consequences
Balance between preventing “hyper”thermia and maintaining an adequate fuel supply to the muscles.
This is an abnormally high core temperature, and has significant implications on performance and health.
What points where highlighted by the video? http://www.youtube.com/watch?
v=ESauS61OHFg
HYPOTHALAMUS
Temperature is regulated by the hypothalamus
Posterior hypothalamus is concerned with heat loss
Controls sweating and skin blood flow responses
Hypothalamic dysfunction?
What do you think the symptoms would be?
HEAT Exchange
Radiation Convection Conduction Evaporation
Hot dry environment 98% of cooling
Activity
With a partner think of as many acute responses to heat as possible.
There are the responses that occur immediately when exposed to the stimulus of heat
And responses that take longer to occur
ACUTE RESPONSES
Acute responses similar to exercise however exacerbated in the heat.
Increase Sweat Response (Most obvious) Increase Skin and Muscle vasodilation Increase Core Temperature
Accute responses to exercise Increase HR
BP Maintenance Takes precedence over skin blood flow
Increase Lactate production
Changes in Substrate Metabolism
CARDIOVASCULAR RESPONSE Progressive decline in Stroke Volume
Due to Sweat losses Increase in HR to compensate Attempt to maintain Cardiac Output ,
progressive loss in Cardiac Output causes a decrease in BP
Extreme Cases – BP regulation wins out over temp regulation
CARDIOVASCULAR RESPONSE....
When Hyperthermia starts to occur
Blood diverted away from the skin Maintain BP IMPLICATIONS
Hyperthermia as no evaporative sweat losses
Risk of Death
SUBSTRATE METABOLISM/ LACTATE PRODUCTION
Increase in CHO usage during exercise in the heat
Epinephrine (adrenaline) levels increase with exercise in the heat
Could result in Increase in Lactate production less ability to oxidise lactate back
to pyruvate
FLUID LOSS
As duration and intensity of exercise increases sweat reponse usually increases?
Sweating helps the body lose heat by....?
How much you sweat is determined by the temperature your training status
FLUID LOSS
2-3L per hour during exercise in the heat Hypo hydration/ Dehydration
Lack of fluid intake/sweat rate Dehydration impairs thermoregulation. Leads to…
Hyperthermia Inability to use cooling mechanisms in
extreme environments may feel dizzy, faint, nauseated, or very
thirsty. Same response to losing a lot of blood
PERFORMANCE IMPLICATIONS Decreases muscular endurance and max
aerobic power
Unsure about the effect on anaerobic performance but research suggests no impact if progressive dehydration does not occur before the event.
PERFORMANCE IMPLICATIONS
Debate over theories Less substrate availability Increased lactate production Suggested critical core temperature Muscle recruitment inhibited during exercise in
the heat Tucker (2004) showed power output began to
fall within the first 30% of maximal self-paced time trial in the heat. This suggested the decrease in performance was not associated with an altered temperature, heart rate or exercise perception.
For next week
An athlete comes to you they have been suddenly called up for a outdoor competition in India during the summer temperatures can reach over 40C, they want advice on what they’re drinking strategy should be.
How much should they drink? Before competition, during and after?
What can they do to maximise fluid retention, is just water enough?
PART 2
Last weeks question
How much should they drink? Before competition, during and after?
What can they do to maximise fluid retention, is just water enough?
Recap
The body defends itself from heat through three mechanisms: breathing, sweating, and changing the blood flow.
The first reaction is to circulate blood to the skin, which increases skin temperature and allows the body to give off some heat.
During heavy work, muscles need more blood flow, which reduces the amount of blood available to flow to the skin and release the heat.
Sweating also helps the body to cool off
humidity levels need to be low enough to allow the sweat to evaporate.
water and salts lost through sweating must be replaced to keep sweating.
Four environmental factors affect the amount of stress an athlete faces in a hot environment area:
temperature, humidity, radiant heat (such as from the sun or a
furnace) wind speed.
Great North Run 2005
Four participants died en-route to South Shields
Particular deadly set of circumstances occurred, High humidity, High temperatures and prevailing tail wind
“they had all been physically fit and well-prepared for the event.”
NUTRITIONALSTRATEGIES
Hyper hydration Chronic, with acclimatization Glucose + Water,Gastric Discomfort, urination,
Increase body mass
Water only Hydration Only replaces 30-70% of sweat losses
Rehydration Water ingested -> dilution of plasma
osmolarity (reduces the concentration of electrolytes)-> reduced thirst
This is why electrolyte and Sodium drinks such as Gatorade and PowerAde are important.
CHO Loading Daily intakes 7-10g/kg of BM
Avoid caffine and alcohol!
IMMEDIATE COMPETITION STRATEGIES TO REDUCE EFFECTS OF HEAT? Athlete or exerciser comes to you
complain of feeling to hot before and during exercise or competition what do you do?
IMMEDIATE COMPETITION STRATEGIES TO REDUCE
EFFECTS OF HEAT Pre Cooling
Ice vests Cold air
Avoiding getting hot too soon reduces physiological strain
Lower Core Temperature Delays dehydration and hyperthermia
Clothing Light weight/ little as possible/Compression
wear
Cooling vest
Compression Wear
there is evidence to suggest that compression clothing may improve exercise performance by reducing the impact of hot and/or humid conditions on the body’s thermoregulatory system
Increases in skin and core temperature and a reduction in cooling efficiency are observed when clothing interferes with the evaporation of sweat from the skin.
It has been suggested that compression clothing assists the rate of evaporation
faster transfer of sweat from the skin to the fabric.
Once there, the sweat can be dispersed more quickly and evenly over a larger area
This Allows evaporation to be maximised.
Athletes would feel cooler during exercise and perceive the activity as being less difficult.
WET BULB GLOBE TEMPERATURE(WBGT)
Estimation of heat stress. WBGT accounts for the levels of
humidity, radiation, wind movement and ambient temperature
WBGT Risk
<18 Low
18-23 Moderate
23-28 High
>28 Hazardous
WBGT Map
ACCLIMATISATION
Repeated exposures to the heat results in adaptations within the body that make the athlete less susceptible to the demands imposed by exercise in the heat.
Heat tolerance is improved
Therefore performance in the heat is improved
STRATEGIES AND DURATION Conflicting Views
Long term/ short term Recent research suggests 7-14 daysMajor adaptations plateau after 14 days
Most of adaptation undertaken 5-6 days
Acclimation Training Artificial Environment Same Intensity and duration
ADAPTATIONS Response & effect
Improved skin blood flow Dissipate heat effectively
Lower Heart Rate Work at a higher intensity
Effective distribution of CO Meet thermoregulation and metabolism demands
Reduction in sweating threshold
Evaporative cooling begins earlier
Increased distribution of active sweat glands
Maximizes evaporative cooling
Increased sweat rate Maximizes Evaporative Cooling
RESPONSERESPONSE EFFECTEFFECT
ADAPTATIONS
Reduction in loss of water and electrolytes from sweat
Preserves sodium in extra cellular fluids, promotes water retention
Better maintenance of Core Temperature
Fatigue delay, increase thermoregulatory capacities
Increasing sweating sensitivity to increasing core temp
Maximizes Evaporative cooling
Less reliant on CHO metabolism
CHO sparing, less lactate accumulation?
RESPONSERESPONSE EFFECTEFFECT
ADAPTAIONS TO MAINTAINCORE TEMP
Sawka et.al (2000)
•Core temperature does not rise as quickly
•Delays onset of dehydration and hyperthermia
•Thermoregulatory responses carried out as normal for longer
BLOOD VOLUME CHANGES
Expansion of blood volume. Large shift of blood to the peripheral
areas. I.e. decrease in plasma volume.
Stimulates increased renal sodium and water retention.
Aldosterone and Vasopressin (ADH) released to help mediate expansion.
HEART RATE
Due to increase in Blood Volume, heart rate decreases rapidly in the first four days of an acclimation program
More blood means the heart doesn't have to work as hard
The HR still increased during exercise, but at a much slower rate after acclimation.
A decrease of about 22BPM from the first day has been shown.
SWEATING
Sweating rate occurs at a lower core temperature.
Rate of sweating increases, more effective evaporative cooling in dry temperatures.
Increased distribution of active sweat glands
Higher Plasma sodium concentrations allows for greater water retention in the body.
Hue et.al (2004) Sweat Rates
HOW CAN THIS HELP??
Acclimatisation allows the body to exercise for longer at a higher intensity in the heat
Body adapts and delays dehydration and hyperthermia
Better thermoregulation Hence, delays onset of fatiguing
elements and increases performance capacity.
Heat Training practical examplesCandian Triathletes training for cancun
mexico competition.
cram 5 people into remodeled 5th wheeler complete with heaters, filters and various other apparatus
crank the heat up to 38c and 80% humidity
Canadian Triathlon Team
ride for 90min with your core temp at 39 degrees
drink as much water as you can handle
get sports "data miner" to collect the stats
Planning for next week
We are in the gym
1 person in each group will be the subject and the subject again the following week
We will weigh them before and after exercise in the same clothes
first week will be with added clothing so subjects must wear long sleeve top and training bottoms. No compression wear underneath!
The week after, either shirtless and only shorts or compression wear.
3 helpers will be on hand for the subject. 1Data collector 1 Minder, to make sure the subject feels ok and
ensures they’re drinking enough water 1 time keeper
Testers should also wear sensible clothing, no jeans
Duration will be 20 minutes moderate intensity level 4 during warm up and then 8 for bikes.
4-6 kph and then 7-9 Kph (avg jogging speed) for treadmill users
First 5 minutes will be warm up and last 2 minutes cool down
We’ll be measuring weight, measuring RPE, and measuring fluid intake
Be sure to bring electrolyte drinks for post test recovery
Pay your testing dues
If you volunteer to be a subject now it means your less likely be one for future testing
If you know what it feels like you will have a greater understand when testing others!