Short report
The incidence of heat casualties in sprint triathlon: The tale of two Melbourne race events

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Summary

Triathlon is a popular participation sport combining swimming, cycling and running into a single event. The Triathlon Australia medical policy advocates the use of wet bulb globe temperature as the criterion for altering race distance and an ambient temperature of 35 °C as a criterion for consideration of cancellation of an event, but there is little empirical evidence detailing the effectiveness of this policy. Nor has the impact of environmental thermal stress on triathletes in shorter duration events been determined. During an injury surveillance investigation of a triathlon race series over the 2006/2007 seasons, two events with similar environmental conditions were completed. One thousand eight hundred and eighty-four participants competed in event 1 (December 2006) and 2000 competed in event 2 (February 2007). Maximum dry bulb (DBT), minimum vapour pressure (VP) and minimum relative humidity (RH) for event 1 were 37 °C DBT, 0.56 kPa VP and 9% RH measured by the Bureau of Meteorology. Fifty-three participants presented for medical aid, 15 due to heat-related collapse. The conditions measured for event 2 were 33 °C DBT, 1.16 kPa VP and 24% RH and there were no heat illness presentations despite 38 individuals presenting for medical aid. These observations suggest that the risk of heat-related collapse is greatest when high-environmental temperatures occur early in the competitive season when participants may be inadequately prepared and have not yet acquired natural acclimatisation to heat. Any Triathlon Australia policy revision could place stronger emphasis on the use of ambient temperature as a limiting criterion for race organisers.

Introduction

Triathlon combines swimming, cycling and running into a single event.1 Races range from 30 min for beginner, to 17 h for ironman, triathlons. Most triathlons are held in summer where the risk of exertional heat illness and hyperthermia is highest. Heat stress arising from hot or humid thermal environments results in high skin temperatures that impose large stresses on the circulatory system and provoke high sweat rates. Circulatory instability immediately following exercise may result in collapse due to hypotension. When the combined effects of intrinsic heat generation and the thermal environment overwhelm homeostatic thermoregulation, exertional heatstroke may occur.2

Policies to minimise the risk of exertional heat illness have been developed1, 3, 4 but little evidence for their effectiveness exists.4 The Triathlon Australia (TA) medical guidelines recommend a wet bulb globe temperature (WBGT) of 26.5° as the trigger for triathletes to exercise caution while competing, and an ambient temperature of 35 °C and WBGT over 29.1° as indicators to suspend events.1 In a recent triathlon race series in Melbourne Australia, two separate days of extreme weather conditions were experienced by competitors. The incidence of severe and non-severe heat-related collapse and injury presentation across these events was compared.

Section snippets

Method

Two events run in similar weather conditions were compared as part of a larger injury surveillance study. Event 1 was completed in December 2006 and event 2 in February 2007. Each event comprised two races; fun and sprint distance. The study was approved by the Monash University ethics committee.

Both events used the same location and comprised a saltwater bay swim, flat cycle course and a flat run course. Event 1's fun (200 m swim, 8 km cycle, 2 km run) and sprint triathlons (500 m swim, 20 km

Results

Competitors completed the event 1 fun and sprint distance races in a mean (range) time of 34:57 (23:43–52:21) minutes:seconds and 1:18:55 (56:34–2:31:57) hours:minutes:seconds, and event 2 in 34:11 (22:00–50:51) and 57:22 (41:47–1:34:05), respectively. The mean (range) duration for the swim, cycle and run in minutes for the event 1 and event 2 fun triathlons were 5:35 (1:48–9:33), 15:27 (7:26–25:09), 10:55 (7:29–17:32) and 4:38 (3:02–7:50), 15:36 (11:59–25:23), 10:48 (7:18–21:38), respectively.

Discussion

This report is an opportunistic addition to a larger injury surveillance study. It is the first to describe the incidence of heat casualties in shorter distance triathlon events held in very similar hot, dry weather conditions. The impact of hot, humid conditions on the presentation of heat illness has been documented for Ironman6, 7 and Olympic distance (temperature: 28–31 °C, humidity 84%)1 triathlons but not for shorter distance races, especially where humidity is low. Fifteen competitors

Conclusion

An ambient temperature of 35 °C and/or a WBGT of 29.1 °C are deemed the criteria for consideration of event cancellation according to TA guidelines. Our study findings suggest that the unexpectedly high incidence of heat casualties in event 1 was at least in part related to the unseasonably hot weather when participants were inadequately acclimatised for endurance exercise in hot conditions. High-environmental temperatures and relatively low humidity coinciding with decreased opportunity for

Acknowledgements

Belinda Gabbe was supported by a Population Health Career Development Award (465103) from the National Health and Medical Research Council of Australia during the preparation of this manuscript.

The authors would like to thank Simon Hood for his assistance with data collection and Super Sprint Events, in particular David Hansen, Jonathan Hocking and Chris Price for their support in completing this project. We also acknowledge the assistance of Dr. John Brotherhood in the preparation of this

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