O'Donnell is a major contender in two of the three titles on offer over the five days of the championships _ today's time trial and Saturday's road race at Buninyong.

She is bypassing tomorrow night's criterium in Sturt St, Ballarat.

O'Donnell knows what it takes to conquer the 28-kilometre Buninyong time trial circuit.

The Victorian stood on top of the podium last time she contested the nationals two years ago.

The sports physician was not so lucky last year.

The 36-year-old, who was a late starter to the world of road cycling, was all set to defend her crown before coming down with a bout of gastro just hours before facing the starter.

O'Donnell told The Courier yesterday that she had a reaction to something she ate on the morning of the time trial.

She said she was doing a media interview about 30 minutes before the event was scheduled to start when it all become too much.

"It was so disappointing.

"And there was nothing I could do about," she said.

O'Donnell, who later this year is hoping to complete a hat-trick of Oceania time trial championships, said she was taking no chances this time, having prepared her own food.

For the first time this year, all men's and women's time trials will be ridden on the opening day.

This is owing to the addition of criterium championships to the program.

The men's under-23 (28km) with 31 entries begins at 10am; women (incorporating the under-23 division) with 48 riders at noon and men (39km) with 41 entries at 2pm.

O'Donnell is ecstatic with the size of the women's field.

"It's fantastic."

She said with past time trial champions such as Sara Carrigan and Oenone Wood having retired, there was a new wave of talent coming through.

"There's some great youngsters and they're all wanting to win."

O'Donnell will be the fifth last rider away at 12.43pm, with only Vicki Whitelaw (ACT), Amber Halliday (South Australia), Olympic gold medallist Kathy Watt (Victoria) and Alexis Rhodes (SA) to follow.

O'Donnell nominated young South Australian Carly Light as one to watch.

"She's very good," she said.