Heat illness and exercise

In order to play and exercise safely in the hot summer months, it is important to understand how the body copes …

In order to play and exercise safely in the hot summer months, it is important to understand how the body copes with exercise in the heat and the guidelines you can follow to exercise safely and optimize your performance.

What is Heat Illness?


Vigorous exercise in sport places some people at risk of heat illness. The risk of illness is obviously greater in hot humid weather because:

  • During high intensity exercise in hot weather people may not be able to produce enough heat for adequate cooling
  • High humidity may prevent adequate evaporation of sweat
  • Heat illness is not a trifling matter- if untreated, it can lead to the rare but life threatening condition of heat stroke. This article will help you recognize and manage potentially dangerous situations that may arise during sport or physical activity, where exertion levels are out of the ordinary.

How do You Tell if Someone has Heat Illness?


Heat illness may occur in strenuous sports, but may also occur in prolonged moderately strenuous physical activity in hot weather. During training and competition exercisers should ‘listen to their bodies’. If they start to experience any of the following signs and symptoms they should stop exercising immediately:

  • Light headedness / dizziness
  • Nausea
  • Obvious fatigue / weakness
  • Muscle cramps
  • Fast and / or weak pulse
  • Collapse
  • Cessation of sweating
  • Ashen / pale / cool / moist skin
  • Confusion / disorientation
  • Altered consciousness
  • Aggressive or irrational behaviour
  • Obvious loss of skill / co-ordination / clumsiness

Types of Heat Illness


1. Muscle Cramps:

  • Mildest form of heat illness
  • Painful muscle cramps and / or spasms during or after intense exercise and sweating in high temperatures

2. Heat Exhaustion:

  • The more common sports related heat illness
  • Is the body’s response to dehydration
  • Participants who collapse after exercise, are likely suffering heat exhaustion, with low blood pressure (postural hypotension), but some may have heat stroke.

2.  Heat Stroke:

  • Is rare, but is a life-threatening condition
  • Those who show signs of altered mental function, loss of consciousness or collapse during exercise are likely suffering heat stroke.
  • Sports participants showing signs of confusion, loss of skill, loss of coordination or irrational behaviour should be stopped and removed from the field immediately.

Factors that Increase the Risk of Heat Illness include:

  • High exercise intensity i.e. Exercising close to personal capacity
  • Lack of fitness (due to insufficient training that includes some at competition intensity and duration)
  • Previous history of heat illness or heat intolerance
  • High air temperature
  • High humidity
  • Low air movement / no wind, following wind while performing exercise
  • Solar radiation
  • Heavy clothing and protective equipment i.e. padding
  • Lack of acclimatisation (due to lack of recent training in warm and humid conditions)
  • Dehydration (inadequate water intake before exercise and during activity longer than 60 minutes)
  • Illness and medical conditions (current or recent infectious illness, chronic health disorders)

What Steps can be taken to Minimise the Risk of Heat Illness?

  • Acquiring Adequate Fitness and Acclimatisation
    Excellent physical fitness markedly increases tolerance. Acclimatisation for sports activities requires at least 5 days of training in hot and humid conditions, progressing from moderate intensity and duration as acclimatisation develops.

  • Adjusting training and Competition Intensity to Conditions
    This should be appropriate to current fitness and weather. In conditions of increased risk athletes should be provided with opportunities to rest for at least 10 minutes per hour. Rest breaks should be maximised by resting in shade, reducing clothing, drinking cool water or sports drinks and using fans to assist in evaporative cooling.

  • Timing of Games or Activity
    Avoid the hottest part of the day between 11am and 3pm. Early morning or night games are recommended.

  • Clothing
    You should allow for easy evaporation from the skin. Key factors include light coloured, light weight, loose fitting items that provide protection from the sun. Wear well-vented broad brim hats and water soluble sunscreen for sun protection. Caps do not provide adequate sun protection.

  • Modifying Warm-Up
    In hot conditions reduce duration and intensity of warm-up, to minimise increase in body heat and temperature before competition.

  • Drinking (Hydration)
    Substantial amounts of water are lost through sweating when exercising vigorously in the heat. To minimise dehydration, drink about 500ml of water in the 2 hours before exercising. During exercise lasting 60 minutes or longer, 500-750ml of cool water / sports drink per hour, are sufficient for most sports. Water intake exceeding sweat loss, in events lasting several hours, can lead to the harmful condition of hyponatremia (low blood sodium).

  • Heat Waves, Unusually Hot Weather and Travelling
    Extra caution needs to be taken in these conditions. Athletes that lack acclimatisation are at increased risk of heart illness if they exercise in the hot weather, at their cool climate intensity.

  • Other Medical Considerations
    If you have recently experienced a high temperature, infection, diarrhoea or vomiting, you should NOT take part in strenuous exercise.

    People who suffer from a variety of medical conditions, who are taking medication or who are pregnant may experience difficulties exercising in the heat i.e. asthma, diabetes, heart conditions, overweight and obesity.

  • Treating Heat Illness

    If an athlete is exhibiting signs of heat illness take the following action:

    • Remove the athlete from the field of play
    • Lay the person down in a cool place
    • Raise legs and pelvis to improve blood pressure
    • Remove excess clothing
    • Cool by wetting skin liberally and use of vigorous fanning (for evaporative cooling)
    • Apply ice packs to groin, armpits and neck
    • Give cool water if conscious

    Athletes Suffering from Heat Exhaustion usually recover rapidly with this assistance. If the athlete remains seriously ill, confused, vomiting or shows signs of altered consciousness, call the ambulance immediately and seek medical help, as they are likely to be suffering from heat stroke.

    Ambient Temperature and Exercise

    Below is a table that will give you an easily understood guide to exercise on hot, dry days.

    Ambient Temperature (°C) Relative Humidity Risk of Thermal Injury Possible Modifying Action for Vigorous Sustained Activity
    15 – 20 Low Heat illness can occur in distance running
    21 – 25 Less than 60% Low Moderate Increased vigilance
    26 – 30 Less than 50% Moderate Moderate early pre-season training intensity. Reduce intensity & duration of play / training. Take more breaks.
    31 – 35 Less than 30% High – Very High Limit duration to < 60 min per Session.
    36 and above Less than 25% Extreme Consider postponement to a cooler time of the day or cancellation

    Treating for Heat Stroke

    • Continue cooling. If available, cool in a shallow canvas / plastic bath of iced water (5-10 minutes)
    • If necessary, cooling should continue during transport to hospital.

    For more information the Bureau of Meteorology provides detailed information about daily temperature conditions in Australia ( Information on sport safety can be attained by going to and clicking on the hot weather icon.



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