Australian travel insurance is limiting.
Usual insurance only covers “racing” if it is a foot race – the foot race/run has a max coverage of 42.2kms (so maximum coverage is a marathon only), thus no insurance coverage for a triathlon, adventure race, some trekking,etc.. Additionally they only provide coverage from trip end to end (i.e. months of travel, around a comparatively short event).

For general travel and racing, the dubiously named insure4less Travel Insurance is the cheapest and covers more than most:

For serious coverage, unlimited activities, unlimited altitude,etc. and specific dates, a reliable option is the aptly named Ripcord Rescue Insurance.
Emergency medical/helicopter search and rescue and evacuation (to $750k) works out to be ~$15US/day. Easy.