HOT COMPETITION If you can’t stand the heat…….
Dec 24, 2015
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