Canberra man's 100 kilometre mission to honour his fallen comrades

But for former Australian Defence Force member Todd Berry it is also a time to reflect on sombre memories from his career in the military.

As a distraction, Mr Berry has challenged himself to run a 100-kilometre ultramarathon to commemorate the Anzac centenary and raise money for physically and psychologically wounded veterans.

Although the ultramarathon will be a test for Mr Berry, it is no comparison to the hardships he faced in the ADF, including losing some of his closest friends.

"Five of my colleagues were killed when we were overseas and that was pretty tough," Mr Berry said.

"I recovered the bodies back to Australia, so I had to spend time with them in the morgue and witness the autopsies."

In his time in the ADF Mr Berry served in infantry and spent a short term in special operations.

He was involved in postings around Australia and overseas.

The Anzac Day Challenge is a 100km ultramarathon endurance trail where participants will run and trek through some of Sydney's remarkable scenic trails in commemoration of the Anzac centenary.

Participants run through the Ku-ring-gai Chase and Garigal national parks to both commemorate the Diggers and their sacrifices and raise money for charities including Soldier On and Mates4Mates who provide ongoing support for soldiers.

"It's a good distraction from Anzac Day for me and a great way to raise awareness and money for Soldier On and I am doing it for my mates as well," Mr Berry said.

He was posted to Canberra between 2004 and 2007, but after 18 years in the Defence Force he decided to stay in Canberra permanently because of the great clinical support network he had established in the capital.

"It will be a great challenge. As part of my recovery it has been really good to have goals. It will be a great physical achievement but also good for me mentally," he said.

Mr Berry has been preparing for more than two months with the help of an ex-commando who wrote him a training program involving strenuous running on different terrains.

"I've been doing a paleo diet for the last five to six weeks and in regards to training we mix it up with short runs, long slow runs, and a few long and short hill runs a week."

He also took part in the half Iron Man competition last November and the Canberra half marathon in April.

Mr Berry will be doing the challenge with a friend he met while posted in Borneo and said he uses the time running to reflect on lost mates.

The Anzac Day Challenge will start after the Dawn Service in Sydney. Participants have 24 hours to make it to the finish line, however Mr Berry hopes to finish the track in less than 15 hours with the support of his wife who will be going to Sydney with him.

He has already gained the support of 52 donors, raising $4300 for the Soldier On foundation with supporters leaving generous donations and comments of pledged support.