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!