hot competition

1
hot competition

• If you cant stand the heat.

2
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.

3
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.
4
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)

5
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

6
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

7

• 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)

8
How to acclimatise

• Raise your body temperature to stimulate sweating
• This must be done in representative temperatures
  (30-35C, 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

9
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

10
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

11
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

12
WOC 2008 The Czech Republic

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

13
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