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Australian community sport extreme heat policies: Limitations and opportunities for improvement

  • Samuel Chalmers
    Affiliations
    Sport and Exercise Science, School of Science and Health, Western Sydney University, Australia

    Thermal Ergonomics Laboratory, Exercise and Sport Science, Faculty of Health Sciences, University of Sydney, Australia
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  • Ollie Jay
    Correspondence
    Corresponding author.
    Affiliations
    Thermal Ergonomics Laboratory, Exercise and Sport Science, Faculty of Health Sciences, University of Sydney, Australia

    Charles Perkins Centre, University of Sydney, Australia
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Published:February 07, 2018DOI:https://doi.org/10.1016/j.jsams.2018.01.003
      The importance of sport in Australian culture is evidenced by 79% of the population aged ≥15 years participating in sport or physical activity one or more times per week.
      • Australian Sports Commission
      Participation data for the sport sector.
      Another defining feature of Australia however is its hot climate. Notably, 2013 was the hottest year on record in Australia and the risk of experiencing extreme heatwaves in summer has increased two-fold in the past few decades.
      • Climate Council
      Cranking Up The Intensity: Climate Change and Extreme Weather Events.
      While fatal heat-related injury during sport is mercifully rare, many cases of heat-related illness during sport and physical activity have been documented.
      • Driscoll T.R.
      • Cripps R.
      • Brotherhood J.R.
      Heat-related injuries resulting in hospitalisation in Australian sport.
      Recent examples include reports of heat exhaustion in nine children during the 2016 Triathlon Championships in Penrith (NSW).

      Australian Broadcasting Corporation. Nine people suffer heat exhaustion at Penrith sports event. Available at: http://www.abc.net.au/news/2016-03-02/nine-people-suffer-heat-exhaustion-at-sydney-sports-event/7215354. Accessed 27 August 2017.

      Moreover, the incidence rate of heat-related health problems at sporting events is likely underreported due to confounding coding and diagnostic issues, especially in the hospital setting.
      • Driscoll T.R.
      • Cripps R.
      • Brotherhood J.R.
      Heat-related injuries resulting in hospitalisation in Australian sport.
      In view of these concerns, many Australian sporting organisations have developed extreme heat policies that stratify the risk of heat illness based on environmental conditions and recommend procedures for cooling participants. The aims of this editorial are to summarise the Sports Medicine Australia (SMA)
      • Australia Sports Medicine
      SMA hot weather policy.
      heat policy and a representative sample of existing heat policies issued at the community level by the six most popular club sports in Australia (according to the 2016 AusPlay survey);
      • Australian Sports Commission
      Participation data for the sport sector.
      and discuss the limitations of these existing policies while highlighting opportunities for improvement through future research.

      1. Sports Medicine Australia heat policy

      The current SMA extreme heat policy,
      • Australia Sports Medicine
      SMA hot weather policy.
      established in 2005 and outlined in Table 1, is arguably the most influential extreme heat policy in Australia. For example, four out of the six representative sport heat policies listed in Table 2 refer to the SMA policy to either set environmental thresholds for activity or provide recommendations surrounding the prevention of heat illness. The guidelines were one of the first forms of heat protection for exercising Australians and the strength of the policy is the ease of access and interpretation for the wider community, especially within the scope of technology at the time of conception.
      Table 1The Sports Medicine Australia (SMA) extreme heat policy environmental threshold guidelines.
      Guidelines based on ambient temperature and relative humidity
      Ambient temperatureRelative humidityRisk of heat illnessRecommended management for sports activities
      15–20 °CLowHeat illness can occur in running
      Caution over-motivation
      21–25 °CExceeds 70%Low-moderateIncrease vigilance
      Caution over-motivation
      26–30 °CExceeds 60%Moderate-highModerate early pre-season training
      Reduce intensity and duration of play/training
      Take more breaks
      31–35 °CExceeds 50%High-very highUncomfortable for most people
      Limit intensity, take more breaks
      Limit duration to less than 60 min
      ≥36 °CExceeds 30%ExtremeVery stressful for most people
      Postpone to cooler conditions (or cooler part of the day) or cancel
      Guidelines based on wet bulb globe temperature (WBGT)
      WBGTRisk of heat illnessRecommended management for sports activities
      <20 °CLowHeat illness can occur in distance running
      Caution over-motivation
      21–25 °CModerate-highIncrease vigilance
      Caution over-motivation
      Moderate early pre-season training
      Take more breaks
      26–29 °CHigh-very highLimit intensity, take more breaks
      Limit duration to less than 60 min per session
      ≥30 °CExtremeConsider postponement to a cooler part of the day or cancellation (allow swimming)
      Table 2Representative sample of extreme heat policies for community-based sporting competitions in the six most popular club sports in Australia.
      SportOrganisationAdult thresholdChildren thresholdActivity changeActivity modification notes
      AFLSouth Australian Amateur Football League40 °C Tan/aCancelled
      38 °C Tan/aGame modifications-Rescheduling
      -Additional in-play cooling breaks
      Association football (soccer)Football New South Wales37 °C Ta32 °C TaCancelled or postponed
      32 °C Tan/aGame modifications-Additional in-play cooling breaks
      CricketSouth Australian Cricket Association37 °C Ta34 °C TaGame modifications or cancelled-Additional in-play cooling breaks
      -Rescheduling
      GolfGolf Australia36 °C Ta and 25%RH
      Slightly modified version of SMA guidelines.
      n/aCancelled or postponed-As per SMA recommendations
      NetballNetball New South WalesSMA guidelines using WBGTSMA guidelines using Ta and RHGame modifications, cancelled, or postponed-Reduced playing time
      -Longer break intervals
      -Provision for extra water
      -Use of a fan
      -Rescheduling
      TennisTennis Australia34 °C WBGT34 °C WBGTCancelled
      30 °C WBGT30 °C WBGTGame modifications-Reduced scoring format
      -Extra break between 2nd and 3rd sets
      38 °C Ta36 °C TaCancelled
      AFL: Australian Football League; SMA: Sports Medicine Australia; Ta: ambient temperature; RH: relative humidity; n/a: not available.
      A Slightly modified version of SMA guidelines.
      A primary opportunity for improvement of the policy is the current disparity between a linear stepwise risk stratification approach and the physiological strain typically elicited by prevailing environmental conditions. For example, according to the International Organisation for Standardisation (ISO) heat stress standard for occupational environments,

      International Standards Organization. ISO 7933:2004 – Ergonomics of the thermal environment – analytical determination and interpretation of heat stress using calculation of the predicted heat strain. Geneva, 2004.

      • Malchaire J.
      • Piette A.
      • Kampmann B.
      • et al.
      Development and validation of the predicted heat strain model.
      conditions constituting the upper boundary of the ‘moderate’ risk category in the SMA guidelines (30 °C ambient temperature [Ta] and 60% relative humidity (RH)) are similarly stressful as those determined as ‘extreme’ (≥36 °C Ta and >30%RH). The environmental heat stress imposed by a given Ta and humidity can be simply expressed using a single value, e.g. a “heat index”.
      • Steadman R.G.
      A universal scale of apparant temperature.
      Fig. 1 illustrates the various combinations of Ta and relative humidity that the heat index equivalent of the ‘extreme’ SMA threshold (36 °C, 30%RH) represents, and a large portion of the ‘high’ zone and approximately one-third of the ‘moderate’ zone of the SMA policy exceeds the same level of environmental heat stress defined as ‘extreme’.
      Fig. 1
      Fig. 1Risk of heat illness stratification according to the existing SMA policy using ambient temperature and relative humidity. Stratification headings are based upon the minimum level of risk within each category.
      Solid line indicates the various combinations of ambient temperature and relative humidity that is associated with the heat index equivalent for the threshold of “extreme risk” as defined by the existing SMA policy (36 °C with 30%RH). The line demonstrates that an identical heat index equivalent temperature can transverse multiple risk categories in the current SMA policy.
      Another limitation of the existing policy is that it does not seem to fully account for very hot (>40 °C Ta) but dry (<15%RH) conditions that often occur across a typical Australian summer. Evidence of the necessity to address this limitation include the 2017 heatwave across New South Wales, which reached conditions of 46 °C Ta in the shade with 14%RH at 4pm on the 11th of February in Penrith. Under such a scenario, the traditional SMA policy would have advised the continuation of play whereas a number of sporting organizations independently chose to cancel competition.

      Levy M, Hannam P, Bagshaw E. Sydney weather: Threat of blackouts on Saturday as NSW bakes in heatwave. The Sydney Morning Herald. Available at: http://www.smh.com.au/environment/weather/sydney-weather-nsw-bakes-in-heatwave-as-warnings-issued-for-pollution-power-cuts-20170210-guam0h.html. Accessed 21 November 2017.

      This decision was advisable as while sweat would evaporate freely with such low ambient humidity, skin surface heat loss would still be limited by the physiological capacity to secrete sweat.
      • Cramer M.N.
      • Jay O.
      Autonomic neuroscience: basic and clinical biophysical aspects of human thermoregulation during heat stress.
      The evidence proposed by the SMA policy regarding acclimatisation may also need reviewing in light of recent research findings. A natural heat acclimatisation is suggested to develop across the course of an Australian summer, which subsequently reduces the risk of heat illness. However, Australian household air conditioning ownership has substantially increased during the preceding decades

      Australian Bureau of Statistics. 4602.2 – Household Water, Energy Use and Conservation, Victoria, Oct 2009. Available at: http://www.abs.gov.au/ausstats/[email protected]/0/503F8B8C2AFD8744CA25774A0013BD64?opendocument. Accessed 19 October 2017.

      and therefore a significant physiological adaptation to the heat may not occur over a summer season due to an inadequate level of exposure.
      • Bain A.R.
      • Jay O.
      Does summer in a humid continental climate elicit an acclimatization of human thermoregulatory responses?.

      2. Heat policies of the six most popular club sports in Australia

      Association football (soccer), golf, Australian football, netball, tennis, and cricket are the six leading club sports in Australia by combined adult and children participation.
      • Australian Sports Commission
      Participation data for the sport sector.
      Ambient temperature and Wet Bulb Globe Temperature (WBGT) remain the two most common environmental measures for defining risk stratification among the extreme heat policies issued to community participants within these sports (Table 2). The argument for using Ta presumably relates to the ease at which it can be understood and accessed by the wider community. However, using only Ta in isolation neglects several critical environmental factors that contribute towards human heat stress; i.e. ambient humidity, solar radiation, and wind. Alternatively, WBGT, which when properly implemented also utilises direct measures of humidity and thermal radiation as well as indirect measures of wind speed, has been a popular indicator of environmental heat stress at the professional sports level and often in occupational environments. However, in order to perform at set of measures in situ to derive a valid WBGT assessment, a specific high quality device is required and can potentially cost >AUD$1,000, which likely deters many community-based clubs. Estimated WBGT is freely available based on air temperature (measured in the shade) and ambient humidity reports by the Australian Bureau of Meteorology.

      Meteorology Bureau of. Thermal comfort observations. Available at: http://www.bom.gov.au/info/thermal_stress/. Accessed 27 August 2017.

      However, it is important to recognise that this is not a true outdoor WBGT value and is calculated based on an assumed moderate sun exposure and light winds.

      Meteorology Bureau of. Thermal comfort observations. Available at: http://www.bom.gov.au/info/thermal_stress/. Accessed 27 August 2017.

      Limitations of the WBGT index, even when measured completely in the sun, include an underestimation of the true environmental strain during times of high humidity or low air movement.
      • Budd G.M.
      Wet-bulb globe temperature (WBGT)—its history and its limitations.
      Cricket Australia presently recommends that extreme heat policies for clubs, schools, and associations be formulated through consultation with the respective state or territory chapter of SMA. For example, the South Australian Cricket Association considers ‘excessively hot weather’ to be 37 °C Ta for adults, at which point coordinators can approve additional drinks breaks or cancellation of matches. However, as of 2016 humidity levels were not included within the environmental threshold. Given that the thermal and cardiovascular strain of a given participant exercising at a fixed metabolic rate and wearing the same clothing would be markedly different between at 37 °C with 10% compared to 50% RH, the inclusion of humidity in future heat stress risk evaluations for cricket would be advisable. Tennis Australia’s nationwide community guidelines for adults (≥17 years) set cancellation thresholds using both WBGT (34 °C) or Ta (38 °C). Tennis organisations that do not have the potential to measure WBGT must rely on the guidelines for Ta, which similarly to the above case example for cricket, do not consider prevailing relative humidity.
      Two sports rely on the threshold guidelines provided by SMA. Golf Australia defer to a slightly modified version of the SMA recommendations based on Ta and RH, and the adult guidelines for Netball NSW are based directly on the SMA WBGT guidelines. Both golf and netball defer to similar guidelines in the midst of vastly different physiological demands, with golf requiring approximately 3.75 METs compared to 8 METs for court-based team ball sports.

      National Cancer Institute. Metabolic equivalent (MET) values for activities in American time use survey (ATUS). Available at: https://epi.grants.cancer.gov/atus-met/met.php. Accessed 4 September 2017.

      A number of football codes operate in Australia. Australian football (termed ‘AFL’ [Australian Football League]) and Association football (soccer) conduct in-season community competitions during the cooler months. There is a vast difference between the environmental threshold for game modifications between nationwide community AFL policies. The South Australian Amateur Football League sets a threshold of 38 °C Ta for game modifications (Table 2) whereas the Victorian Amateur Football Association prescribes a threshold of 30 °C Ta (not listed in summary table). Similar to many sports, this clearly indicates a lack of evidence-based research to inform consistent heat policies. Humidity is not acknowledged within the South Australian Amateur Football League policy nor are recommendations provided for training sessions, which is relevant for pre-season training that typically occurs during summer. In regards to Association football, the cancellation threshold for adult (≥17 years) competition set by Football New South Wales only refers to Ta (37 °C), and also omits the inclusion of humidity.
      Some policies outlined in Table 2 provide different environmental thresholds between adults and children. However, the rationale supporting the change in thresholds or heat indices in comparison to adults is unclear. Moreover, the Football New South Wales children’s heat policy potentially imposes significant restrictions in the Western Sydney region during the summer community pre-season period. For example, a total of 39 days (43%) during the 2016/17 summer (November–December) exceeded the minimum cancellation threshold (32 °C Ta) at 3 pm in Penrith, NSW. The legal ‘duty of care’ for ensuring the wellbeing of children engaging in physical activity is clear. Numerous clinical and public health organizations, including SMA, state that children have thermoregulatory impairments that render them more susceptible to heat-related illness.
      • Australia Sports Medicine
      SMA hot weather policy.
      • Bergeron M.F.
      • Devore C.
      • Rice S.G.
      Policy statement—climatic heat stress and exercising children and adolescents.
      However, recent evidence supporting an independent influence of developmental age on thermoregulatory capacity is unclear following methodological advances.
      • Cramer M.N.
      • Jay O.
      Selecting the correct exercise intensity for unbiased comparisons of thermoregulatory responses between groups of different mass and surface area.

      3. Common cooling strategies featured in Australian extreme heat policies

      Simple cooling methods must be considered for community-based competitions that typically occur in relatively low-resource environments. The most common strategy advocated is the provision of additional breaks. While this strategy intuitively reduces the rate of rise in core temperature due to a temporary decline in metabolic heat production, it remains possible that the prolonged overall exposure to hot and still conditions, when the temperature gradient for dry heat transfer is reversed (i.e. air temperature >35 °C) and the convective component of evaporation is restricted, the large reduction in self-generated air flow across the skin may offset any transient net cooling effect.
      • Deren T.M.
      • Coris E.E.
      • Casa D.J.
      • et al.
      Maximum heat loss potential is lower in football linemen during an NCAA summer training camp because of lower self-generated air flow.
      The additional rest period may also encourage players to compete at a higher intensity (resulting in a higher metabolic heat generation) following the resumption of play and potentially nullify any positive thermoregulatory benefits. It therefore may be beneficial in community-based sports for the additional cooling breaks to form part of the actual match time rather than extending the overall exposure to reduce the risk of exertional heat illness.
      The regular provision of fluids to reduce the risk of heat illness is advocated by all extreme heat policies listed in Table 2. The emphasis placed upon dehydration should not however distract from evidence demonstrating that a high core temperature (>39.5 °C) during exercise can still occur in the presence of only modest levels of dehydration (<1% body mass loss).
      • Périard J.D.
      • Cramer M.N.
      • Chapman P.G.
      • et al.
      Cardiovascular strain impairs prolonged self-paced exercise in the heat.
      Ultimately, dehydration can negatively influence thermoregulation,
      • Montain S.J.
      • Coyle E.F.
      Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise.
      but the level of dehydration needed for meaningful thermoregulatory impairments to occur must be considered in the appropriate context for community sports. For example, the classic study by Montain and Coyle
      • Montain S.J.
      • Coyle E.F.
      Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise.
      demonstrated that >80 min of continuous exercise at a rate of oxygen consumption of over 3 L min−1 at 33 °C, 50% relative humidity with total fluid restriction is required for a greater elevation in core (rectal) temperature to occur in comparison to partial (approximately half the fluid lost as sweat) fluid replacement. While we recommend that hydration guidelines should remain in place, a greater emphasis should perhaps be placed on advocating effective exogenous-based cooling strategies.

      4. Future opportunities for heat policy improvement through future research

      The current stepwise risk stratification format of the SMA extreme heat policy, issued in 2005, was necessary for the ease of interpretation and widespread use at the time. However, the relatively recent emergence of advanced smart technology and wireless access to freely available weather information presents opportunities for the development of a modernized heat policy that issues an assessment of heat stress risk on a continuous scale that not only estimates risk based on Ta and humidity, but also wind speed and shade. There is also the opportunity to develop heat policies that are customized to the different physical and clothing requirements across a range of sports. Further evidence is required to inform the development of extreme heat policies for children. Do children need revised policies in comparison to adults? Identifying whether any true impairments of thermoregulatory capacity exist in children is essential for developing extreme heat policies that do not unnecessarily ‘overprotect’ children, since this may ultimately result in organisations dangerously disregarding recommendations. In-play breaks appear the most feasible potential cooling method, however, research is lacking that evaluates the effectiveness, optimal duration, and timing of breaks.
      • Chalmers S.M.
      In-play cooling strategies for sport in hot and humid conditions.
      A further exploration is needed of the importance of hydration in the development of heat illness in community sports, accounting for typical duration, sweat rates, and rehydration practices at the amateur level.

      5. Conclusion

      The recent emergence of advanced smart technology and wireless access to meteorological information presents an opportunity to deliver modern heat policies directly to end-users in the community. However, it is essential that these polices are evidence-based and as such provide adequate protection for participants, but equally do not ‘overprotect’ to the extent that organisations disregard recommendations and therefore create a policy vacuum. Opportunities also exist for policies to be developed and delivered for specific sports and participants characteristics. Future work is required to better understand appropriate environmental risk stratification limits for children relative to adults, as well as the efficacy of a number commonly advocated but under researched cooling strategies.

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