However, two Olympians are particularly excited. Michael Shelley and Lisa Weightman​ have each competed in at least one Olympic games, as well as countless marathons all over the world. Now, they come to Sydney.

"I just love running with all of the happy runners in such big races, it is extra motivating knowing that everyone on the start line is about to achieve something amazing," said Ms Weightman, who will run the SMH Half Marathon for the first time on Sunday.

The race has so far raised over half a million dollars for more than 800 charities, with thousands of entrants already signed up to run the 21.1-kilometre course.

Mr Shelley, who won the race in 2014, said his favourite thing about the course is being surrounded by the "iconic" landmarks.

"I enjoyed the course ... you don't get many opportunities to run through the streets of Sydney and run past those iconic landmarks," he said.

Ms Weightman, who runs about 150 kilometres a week, said the key to a successful long distance run is making sure you don't feel alone. She suggested always training with a friend.

"Running is so much more enjoyable when you have someone to do it with ... as long as I am running with my husband I am happy to run anywhere!" she said, encouraging others to do the same on race day.

"Even if you don't know the person in front of you, catch up to them and run and support each other through the journey and try to peg off the next person. It is a really rewarding experience joining forces and achieving personal bests together."

As for any final advice?

"Cut your toenails before you race so you don't experience any discomfort due to your toenails cutting into other toes," said Mr Shelley.

The Sydney Morning Herald Half Marathon is on Sunday the 15th of May. Entries for the run close 5pm Saturday May 14.