TRAINING AND RACING IN HEAT AND HUMIDITY

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TRAINING AND RACING IN HEAT AND HUMIDITY

• Michael Turnbull
• 8th October 2005

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INTRODUCTION

• Physiology in the heat
• Performance in the heat
• Heat acclimatization
• Adaptations
• Gender and age differences
• Dehydration
• Heat injuries
• Loss of acclimatization
• Summary
• Questions and Answers

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PHYSIOLOGY IN THE HEAT

• Exercise in Asia poses a particular stressful
  challenge to the maintenance of normal body
  temperature and fluid homeostasis
• Heat and humidity reduce the bodys ability to
  lose heat resulting in a greater core temperature
  and a higher sweat rate compared to the same
  exercise in a moderate environment.

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PERFORMANCE IN THE HEAT

• Triathlon performance is impaired in hot and
  humid environments
• Contributory factors include
• Hyperthermia Impairs Central Nervous System.
• Muscle blood flow changes Muscle blood flow is
  reduced due to competition between the working
  muscles and the skin.
• Metabolism Muscle glycogen usage is increased
  and lactate production is elevated
• Leads to an increased risk of heat injury

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HEAT ACCLIMATIZATION

• Acclimatization by repeated exercise in the heat
  (either strenuous interval training or continuous
  exercise above 50 VO2 max) promotes higher core
  temperatures.
• This results in physiological adaptations that
  increase heat tolerance
• Increased plasma volume
• Earlier onset of sweating
• Higher sweat rate
• Reduced sodium chloride loss in sweat
• Reduced skin blood flow

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HEAT ACCLIMATIZATION

• After acclimatization, the increased sweat rates
  improve the ability to control body core
  temperature, leading to an improved performance
  capacity.

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GENDER DIFFERENCES

• Most women appear to be less heat tolerant than
  men.
• Contributory factors include
• Lower sweat rates
• Generally higher percentage of body fat
• However, when men and women are matched for the
  same acclimatization and similar body
  compositions gender differences in the
  physiological responses to thermal stress are
  small.

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AGE DIFFERENCES

• Does ageing impair your ability to thermoregulate
  and exercise in the heat?
• Previously controversial in earlier studies
• More recent studies have shown that heat
  tolerance does not appear to be compromised by
  age in healthy and physically active older
  subjects
• Physical deconditioning and a lack of heat
  acclimatization are more likely causes of a
  decline in performance

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DEHYDRATION

• An earlier onset of sweating at a higher rate can
  lead to potential dehydration
• Sweat loss can reach up to 3 litres per hour in
  some athletes
• A 5 loss in body weight through dehydration can
  lead to a 30 loss in exercise capacity
• Even if hydration techniques are correct, it has
  been reported that some marathon runners can lose
  8 of their body weight in one race

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HYDRATION RECOMMENDATIONS

• Dehydration can be avoided through correct
  hydration techniques
• Be adequately hydrated prior to the exercise (400
  800ml of fluid 2 3 hours before)
• During the exercise, most athletes should consume
  between 150 300ml of fluid every 15 to 20 mins
  (PRACTICE!!!)
• Following the exercise, replace what you have
  lost
• Drink cold drinks, they are absorbed by the body
  faster
• Fluid replacement during exercise reduces heart
  rate, body temperature and perceived exertion
  levels
• For triathlons, water alone is not enough
• Electrolytes lost through sweating need to be
  replaced

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HEAT INJURIES

• Symptoms include
• Nausea, dizziness, reduction in sweat rate and
  general ability to think rationally
• To prevent overheating
• A maximum surface area should be exposed for
  evaporation
• Frequent water breaks couple with rest periods to
  allow the core temperature to decline
• If the symptoms have already developed
• Stop exercising
• Drink water or a balanced electrolytic drink
• Submerge the body in cool water

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LOSS OF ACCLIMATIZATION

• The rate of decay of heat acclimatization is
  rapid
• Reductions in heat tolerance can occur within a
  few days of inactivity
• Heat tolerance can decline significantly within 7
  days of no heat exposure.
• A complete loss of heat tolerance can occur
  following 28 days of no heat exposure.
• Repeated exposure is required to maintain
  acclimatization.

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PROMOTING HEAT ACCLIMATIZATION

• Training in sweat clothing in a cool environment
  can promote heat acclimatization
• The magnitude of acclimatization is generally
  less than training in a hot and humid environment
• BUT artificial heat training appears to be better
  than attempting no heat acclimatization measures.
• Important for those of you who travel to Europe

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SUMMARY

• Heat and humidity have a negative effect on
  performance.
• Heat acclimatization can improve performance
• A side effect of acclimatization is a greater
  risk of dehydration
• Maintain hydration!
• When moving to a cooler climate for a short
  period of time, train in the heat