During a week of cycling in scorching South Australia, Wayne Henderson lost four kilos, trimmed 6 per cent of his body fat and every day burned 4000 calories.

The Paihia resident was among a group of five who cycled about 800km from Geelong to Adelaide to raise funds for Casa Herbalife, a charity that provides food, clothing and shelter for at-risk children around the world.

A cycling novice, he bought a bike only three months ago and with only a few days' practice, hit the road last week in searing heat of up to 49C.

Much of Victoria and South Australia was gripped by the worst heatwave in decades. With temperatures reaching the mid-40s, people rushed to shopping malls and cinemas to get some cool air.


Players at the Australian Open tennis in Melbourne also struggled in the heat and urged organisers to shift match times.

Mr Henderson said the idea to ride for charity was sparked by his 58-year-old Aussie friend, Kevin Beale, who found a mountainbike by the roadside in Brisbane.

"I bought a bike and started pushing the paddles around and with a bit of practice in Geelong, we set off on January 10 and arrived in Adelaide on the 17th (January) with three support crews in three vehicles," Mr Henderson said.

The group would do 150km on most days and the longest they rode was 195km.

When they set off, the weather was bearable but all that changed on day two of the cycling.

"The temperature shot up to 42 degrees, with a strong head wind and hills on the way, and although we were well-protected against the elements, we still needed to breathe," he said.

"It was the most difficult thing I ever had to do but equally rewarding as we raised $17,000, but figures are still coming in and we expect the collection to top $20,000, which is a good result."

Mr Henderson said he'd lived all over the world in hot and cold temperatures but had never experienced anything like the heatwave in South Australia last week.

"We needed probably two litres of fluid every 25km and stopped every 30 to 40km for food and drinks."

He said the crew heard about a resident whose cycle tyres had popped from the extreme heat.

"Even you could hear the tar popping as we rode in 49C and we actually recorded the temperature on our GPS units."

In Victoria, people were still suffering from the effects of the heatwave even though the weather had cooled substantially.

In most of the state, temperatures were back in the 20s instead of the 40s.

By Sunday last week, paramedics had dealt with almost 500 heat-exposure cases and almost 190 cardiac arrests since Monday last week.

On the last day of the heatwave, Friday, there were 77 cardiac-arrest calls - seven times the usual rate.