HOT COMPETITIONIf you can’t stand the heat…….

Performance Impairment

Loss of fluid, as well as wider distribution throughout the body of the already depleted fluid volume means the heart has to work harder in order to continue to supply the muscles and organs with blood.

Dehydration 1-5% body mass loss due to

dehydration: 5-50% reduction in endurance

performance; 10-22% reduction in VO2max

Increases temperature due to decreased sweating and cutaneous blood flow : 3.7% decrement in 1500m pace (6s),

6-7% decrement in longer events Benefits of heat acclimatisation are

negated The risk of heat illness is increased(Armstrong et al 1985; Craig & Cummings 1966; Pinchan et al, 1988) From: Rowell L B. Human circulation. Regulation

during physical stress. OUP, 1986.

Hyperthermia & Central Fatigue There is a diminished

central drive to exercise in hyperthermic individuals

Cerebral blood flow falls due Hyperventilation Fall in CO and BP

Brain temperature increases Brain sensitive to heat Affects cerebral cortex

Nielsen & Nybo, 2003)

Heat & Performance Marathon performance

declines 1 minute for each 1 °C increase in air temperature above 15 °C (Maughan, ABC of Sports Med)

Compromised muscle and hepatic blood: earlier onset of anaerobic metabolism and blood lactate accumulation

Muscle glycogen utilisation is increased: fatigue occurs earlier during prolonged moderate exercise in the heat

Variables that affect response to heat Environmental conditions Body size (mass, skinfold

thickness) State of training / sudden

increase in tempo Degree of acclimatisation Hydration status Clothing worn State of Health : fever, viral

illness, cold, GI disturbances

Genetic profile: responsiveness to heat

Genetic disorders: malignant hyperthermia

Skin disorders - sunburn over 5% of body surface impairs thermoregulation for 21days

Use of medication - diuretics, antihistamines

Sweat gland dysfunction (e.g. prickly heat)

Salt depletion Age

Heat, Fitness & Performance: Aerobically fit individuals are

able to perform for longer in hot environments, and tolerate higher levels of hyperthermia than less fit individuals but

Abnormally high core temperatures impair exercise performance in all individuals in the heat, irrespective of fitness

Fatigue generally occurs with core temperatures between 38 - 40 °C (Hales et al, 1996 & Nielson et al 1997)

How to acclimatise Raise your body temperature to

stimulate sweating This must be done in representative

temperatures (30-35°C, 100min per day optimal)

It is important to exercise during these exposures (but the mode is unimportant and intermittent exercise is OK)

Acclimatisation is specific to the climate and activity level i.e. The best would be to train in the same conditions as you will experience on race day.

You should allow 10-14 days to acclimatise with no more than 3 days elapsing between successive exposures. 66-75% of changes occur in 4 to 6 days

Fitter individuals can acclimatise more quickly (7-10 days)

Even fit individuals need to exercise in a hot environment

On return to a temperate climate, the major benefits are retained for a week, 75% are then lost within 3 weeks

Acclimatisation Aldosterone secretion increases and

increases sodium & chloride reabsorption in sweat ducts and renal tubules. This results in lowered salt content in sweat (e.g. sweat sodium reduced from 50 to 25mmol.L-1) and increased osmotic retention of water, producing increased plasma volume

Increased sensitivity to aldosterone Less cardiovascular strain, perfusion

pressure better maintained More effective distribution of cardiac

output

Improved cutaneous blood flow Earlier onset and greater rate of

sweating & gland recruitment Lower resting deep body

temperature Lower skin and deep body

temperatures for a given level of exercise

Improved physical work capacity Increased comfort Decreased reliance on carbohydrate

metabolism

Reducing the impact of the Environment

Acclimatisation Hydration/Rehydration Cooling (Clothing, ice

baths) Cooling stations: fans,

shade, source of cold water & drinks

Maintaining comfort (e.g. In accommodation, at prestart, after the race)

Pacing strategy

ClothingShould be Lightweight Light in colour Breathable/open weave Loose Absorbent The main function of

clothing should be to assist the evaporation of sweat

WOC 2008 – The Czech RepublicThe warmest month of the year in the Czech Republic is July. On average, the summer temperatures are about 20°C higher than during winter. Especially in the last decade, temperatures above 30°C are not unusual. Summer is also characterized by rains and storms.

What is the heat stress in Czech?

July Data Average High Temperature 22.2

°C Average Low Temperature 12.2 °C Average Mean Temp 17.2 °C Average Morning Relative

Humidity 81% Average Afternoon Relative

Humidity 54% Record High 36.1 °C Record Low 5 °C

Heat Stress Index – Temperatures in CelsiusHeat Cramps

Heat ExhaustionHeat Stroke

RH (%)

21.1 23.9 26.7 29.4 32.2 35 37.8 40.6 43.3 46.1 48.9

0 17.7 20.6 22.8 25.6 28.3 30.6 32.8 35 37.2 39.4 41.710 18.5 21 23.5 26.7 29.4 32.2 35 37.8 40.6 43.9 46.720 19 21.6 24.5 27.8 30.6 33.9 37.2 40.6 44.4 48.9 54.430 19.4 22.8 25.6 28.9 32.2 35.6 40 45 50.6 57.2 64.440 20 23.3 26.1 30 33.9 38.3 43.3 50.6 58.3 66.150 20.6 23.9 27.2 31.1 35.6 41.7 48.9 57.2 65.660 21.1 24.4 27.8 32.2 37.8 45.6 55.6 6570 21.1 25 29.4 33.9 41.1 51.1 62.280 21.7 25.6 30 36.1 45 57.890 21.7 26.1 31.1 38.9 50100 22.2 2.7 32.8 42.2