HOT COMPETITION If 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. SweatingDehydration Cardiovascular Insufficiency VasodilatationOverheating Impaired Performance

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 °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 days to acclimatise with no more than 3 days elapsing between successive exposures % 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

Clothing Should 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 Republic The 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 Celsius Heat Cramps Heat Exhaustion Heat Stroke RH (%)