The ACT Brumbies, Canberra Raiders and Canberra United melted in the capital's 38-degree heat on Thursday as they trained in soaring temperatures.

The Brumbies and United moved their training times to avoid the brutal conditions, and the Raiders were on the field as the temperature hit 38.8 degrees.

But Australian Institute of Sport exercise physiologist Meg Ross said exposure to the heat could benefit athletes if they prepare and recover adequately.

Athletes can lose up to two kilograms after an hour training in extreme heat. Body temperature can also rise two degrees after just 40 minutes of physical activity. Ross, who did a PhD in pre-cooling and went to the Beijing Olympics to help lower athletes' core temperatures, said prolonged activity in extreme conditions was harmful.

''You can do strategies to avoid the heat or you can play and train in it so you're used to it,'' Ross said. ''Heatstroke is rare and extreme. When the core body temperature gets to 40 degrees, that's when it can be potentially life-threatening.

''But it's not all bad. An exposure to heat is the best way to become acclimatised, but you don't want to do it to the point where you're fatiguing.

''You have to train in these sort of conditions if you want to be able to compete and cope with them in a game situation.

''If the environment is hotter than we are, and it's indoors, it becomes a heat chamber and athletes are only building heat.''

Ross said ice slushies or dunking towels in water and wrapping them around the body were the best ways to ''get bang for your buck in cooling''.

Raiders, Canberra Capitals and United doctor Wilson Lo warned athletes against increased activity in the heat. Lo suggested United move its game against Adelaide on Sunday away from its 3pm timeslot, which has been the hottest part of the day in the past week.

''When you're dehydrated … your blood pressure can drop, you can get dizzy and in extreme cases it can cause heart problems,'' Lo said. ''It's dangerous to train and, in particular, to play in the heat. If the dry heat gets to 32, that's when you have to modify things and have more drinks breaks.

''When it hits 38 degrees, the recommendation is to postpone or cancel a game. Once you're dehydrated to 1 per cent, that affects your performance.''

The Capitals and United are preparing safety back-ups for their respective WNBL and W-League matches this weekend.

Football Federation Australia denied United and Lo's request to delay the kick-off in its match against Adelaide. However, a W-League official will monitor conditions and it's likely both teams will agree to a drinks break 20 minutes into each half.

The Capitals will play in a ''tin shed'' at Tuggeranong on Saturday with no airconditioning and the temperature set to reach 40 degrees. At times, temperatures inside the stadium are up to four degrees hotter than outside.

Capitals coach Carrie Graf has investigated using ice vests and there is a Basketball Australia extreme-heat policy when the temperature is above 38 degrees.

''We've been heat conditioned in the tin shed, we trained at Tuggeranong on Tuesday and Wednesday and we've got some fans for the bench,'' Graf said.

''It happens every year, we're used to it. We've got fans set up, we looked at using ice vests but by the time players get them on and off on the bench, and they take effect, they don't really work.''

Canberra's hot week will continue on Friday and Saturday with forecasts for 39 degrees and 40 degrees respectively.

The Raiders opted against changing their schedule and set up a marquee with a sprinkler to keep players cool on Thursday.