The sporting icons will each do a 10km run and 20km cycle when they team up for the annual Monster Challenge in September.
The Highland event will be former Scotland rugby captain Hastings’ third duathlon and one he lists as a highlight in Scotland’s sporting year.
He said: “I will take on the Monster for the third time on September 11 and, as always, my aim is to get round in one piece.
“For an event of this nature to sell out year on year demonstrates just how enjoyable it is – the team spirit, the views, the organisation and the course itself are first class.
“It has become one of the highlights of my year.”
More than 1,000 competitors have signed up in teams of four to run and cycle around the shores of Loch Ness on in the 11 September race, organised by FirstGroup.
Olympic Gold Medal 400m hurdler, Sally Gunnell, said she hopes the event will raise a six-figure sum.
She said: “I’ve been training hard so hopefully I won’t let Gavin and my other two team mates down.
“The main aim of the event is to raise money for good causes and in particular First’s charity partner, Save the Children.
“More than £170,000 was raised in 2009 – I hope we can beat that total.”
The challenge has been officially accredited by the British Triathlon Foundation and consists of teams of four, with each competitor aiming to complete one 10km run and one 20km cycle.