DOES acclimatisation make a difference to an athlete's performance in hot weather? Can it help prevent heat illness? How much is enough - or optimal?

Writing in the latest (February 2008) edition of the Journal of Science and Medicine in Sport (JSAMS), a team of Monash University researchers led by Mr Cameron Gosling detail more evidence for the importance of acclimatisation.

The Monash team used injury data from two triathlons held as part of the 2006/2007 triathlon series. Weather conditions were virtually identical for both.

At the first, held in December, there were 15 heat-related injuries; the second, held in February, had no heat injury presentations.

Cameron Gosling puts this difference down mainly to the fact that by February, the athletes were better acclimatised to the hot weather.

"This evidence suggests that the risk of heat injury is greatest earlier in the season when athletes may be inadequately prepared and have not yet acquired natural acclimatisation to heat," Mr Gosling said.

"Another telling piece of evidence was that the first race day was markedly hotter than the preceding 10 days, making it even harder for the participants to have been acclimatised.

"For the second race, event organisers followed Sports Medicine Australia recommendations for exercising in hotter conditions and made a number of changes including an earlier start, reducing the race length, increasing drink station numbers and providing increased education to participants about heat illness.

"Event planners must be prepared to provide medical assistance for post-exercise collapse, which could include heat stroke, regardless of the environmental conditions," Mr Gosling said.

Sports Medicine Australia recommends at least five days of training in hot or humid conditions, progressing from moderate intensity and duration as acclimatisation develops.

However, event organisers, especially for events requiring sustained exertion from participants - such as triathlon - need to be aware heat illness can occur even in cool conditions and with well-hydrated participants.