Exercising in extreme environments is known to be associated with medical complications. The American College of Sports Medicine has developed guidelines for exercising in a hot environment. These guidelines were developed to provide advice during endurance events, in particular, distance foot races. The ACSM recommended using, an on-site Wet Bulb Globe Temperature (WBGT) reading and recommended that consideration should be given to cancelling events when the WBGT was above 28.
Rugby is a team sport played by athletes of varying stature where the game is of an intermittent nature and limited to two 40 minute halves. The intermittent nature of the sport probably allows for greater access to fluid intake during competition when compared with endurance events.
Considering the significant differences between endurance foot racing and Rugby, a review of other sports Heat Guidelines, more closely aligned to Rugby was undertaken. This investigation revealed that the National Rugby League (NRL) in Australia had developed Heat Guidelines during 2000 following research undertaken by Dr John Brotherhood.
The outcome of this research revealed that “relying on the WBGT was limited as it only took into account ambient temperature, globe temperature (radiant heat) and humidity and 70% of this reading was dependent on humidity”. In addition it was identified that “the WBGT was not recorded by weather bureaus and a figure had to be estimated from the Wet Bulb Temperature”.
Dr. Brotherhood placed more weight on the Belding Hatch Stress Index (BHSI) than the WBGT. BHSI is calculated by dividing the Evaporative requirement of the player by the Maximum Evaporative capacity of the environment x 100. A figure of 100 represents an equilibrium between heat loss and heat gain.
In 2001 the NRL adopted guidelines based on the Heat Stress Index measured using a Whirling Hygrometer to assess environmental conditions. Since the introduction of these guidelines there has not been a reported incidence of heat illness during a competition game.
The recommended guidelines are based on utilizing the Heat Stress Index as measured by the Whirling Hygrometer at the site of the game.
Heat illness can range from heat exhaustion to heat stroke, with heat stroke being a
potentially fatal illness.
Heat stroke develops when the rate of heat production by the body exceeds the rate of heat loss and total body temperature rises to a level that leads to organ dysfunction and collapse.
Many factors influence the onset of heat illness and their significance should be recognised when exercise is undertaken in a hot environment. It should however be recognised that it is very difficult to identify with certainty that an individual will suffer heat stroke.
A core body temperature above 38 degrees Celsius is present when an individual experiences a heat illness. Major factors known to influence the core body temperature of an athlete are listed below.
Research has not identified a specific temperature and / or humidity when exercise is not recommended.
The following are the critical steps in minimizing heat illness during competition and training:
Players should be advised to:
Coaching, management and medical staff should:
If practical, training and playing should be scheduled when ambient temperatures, radiant heat (direct sunlight) and humidity are expected to be at acceptable levels. Utilising the Heat Stress Index, a guide to acceptable levels would be:
There is no evidence to suggest training or playing at higher temperature and humidity levels will result in a heat illness.
Historical data should be obtained from the local Bureau of Meteorology to identify times throughout a day and month when these conditions are most likely to prevail. This information can then assist with scheduling training to minimize risk.
Allowing athletes to acclimatize should also be a component of managing potential heat illness. Activity in hot humid conditions should be introduced gradually to allow athletes to acclimatize to these difficult conditions.
Acclimatisation is reported to occur following 7 – 10 days of exposure to the appropriate environment.
In extreme weather conditions an objective assessment of the environment may be required to assist in determining the safety of the prevailing conditions.
Research and experience has confirmed that the “Heat Stress Index” measured using a “Whirling Hygrometer” is both practical and reliable and it is recommended that each Rugby Ground have access to a Whirling Hygrometer to measure the weather conditions. This Index (see attached chart) takes into account Air Temperatures at various Relative Humidity. Prior studies have confirmed that if the Heat Stress Index % is below 150, the risk to players should be minimal. Experience suggests that players are able to cope with an Index as high as 250 but it is recommended that all of the Heat Illness Prevention Interventions listed below are applied if the Index is above 150.
From a practical perspective, the hygrometer needs to be whirled for 20 seconds to obtain readings. Three measurements should be undertaken and averaged.
The Whirling Hygrometer (≈ $A 175) can be obtained from Arthur Bailey Surgico Pty Ltd 55 Lilyfield Road Rozelle 2039 NSW. Ph – (02) 9555 1588.
Whilst the Heat Stress Index has been successfully utilized in Australian Rugby League the IRB recognizes that Rugby players are potentially at a higher risk of a heat illness than Rugby League players. The reasons for this opinion are listed below and have been taken into account when formulating the IRB Prevention Interventions:
The following Game Day Interventions should be implemented when the Heat Stress Index is above 150:
It should be noted that increasing access of water carriers to the field has not been recommended as it is felt that there is adequate breaks in the course of a game to allow water carrier access and player re-hydration.
The recommendations re education, scheduling and acclimatization should also apply to training sessions.
Training sessions are more easily manipulated and the following is recommended during periods of significant heat stress (Index > 150):
In addition the following are also recommended:
Each training and playing venue should have in place a crises management plan. This plan should reflect that prompt recognition and immediate total body cooling will resolve or mitigate the problems of hyperthermia.
These Heat Guidelines are intended to minimize the risk of the onset of heat illness and provide a framework for each team and venue to operate safely during periods of climatic extreme.