Push-ups press the message of suicide prevention

Which is why his suicide at the age of 22 came as an unimaginable shock to his loved ones, including his older sister Annie Halloran.

"He was just one of those people where life was never too big for him," Ms Halloran told AAP.

"He would be the first to jump up at an opportunity or the first person to go: 'right, let's do something crazy today'."

Mr Halloran served in the army, based in Darwin, and had a wide reach of friends around the world, his sister says.

But no one was prepared for what happened.

"We didn't know he was struggling at all - it came as quite a shock to us," she said.

"A lot of us have had to sit with that. Everyone has thoughts of, 'what could I have done differently? What could I have done better?'

"Then the conversation turns to, 'what could we do for the next person, so that we're not having another Tom lost in the community?'"

Ms Halloran and her parents do not want to let Tom's loss be in vain and are determined to use his story to help destigmatise mental health and get more people talking openly about their struggles.

This year, Ms Halloran will be taking part in the Push-Up Challenge and attempting to do 3249 - the number of Australians who lost their lives to suicide in 2022 - across June to improve suicide awareness and raise money for mental health resources.

CEO Nick Hudson came up with the challenge eight years ago with a few mates. The four of them wanted to get fit and challenged themselves to do as many push-ups as they could in a month.

"What we didn't realise was how much this challenge we set ourselves would keep us connected," Mr Hudson said.

"Over that month, we'd check in to see how we're going with the push-ups and then the conversations would quickly evolve into something else.

"'Marty - I see you haven't done any push ups today, why's that?'

"It became this connection that gave me the inspiration to think - maybe there's something more than this."

The following year, 1000 people had joined in the challenge. Last year it was 215,000.

It was during the third year - when Mr Hudson experienced his own depression - that he realised how important those connections had become and threw everything at growing the challenge to benefit more people.

"If you want to have a chat with someone about mental health or a lot of personal things, it's great to have those chats in an incidental way," he explained, adding that the challenge was particularly popular with younger men.

"You don't necessarily sit someone down and face-to-face say 'mate, what's going on?'. It's those chats when you're walking along or you're playing sport or you're driving along together and it's not as intense - you don't have that piercing eye contact."

There is no obligation to stick to push-ups. Sit-ups, squats or lunges are OK too.

Participants have been as young as five and as old as 105.

Some people come along not really knowing it's a mental health event just to "have a bit of fun", Mr Hudson says.

"But then they get involved in the mental health dimension and that levels up their mental health literacy, which is something we're quite proud of."

Serena O'Callaghan is about to take part in her fifth Push-Up Challenge - an endeavour she says has helped her come to terms with her own grief.

It was only a few months after her first challenge, in the depths of an interminable Melbourne lockdown, that a very close girlfriend took her own life.

"The really crushing thing is we were really similar in a lot of ways," she said.

"We both openly talked about our mental health and what we had to do to maintain it. Both had spicy Asian families.

"It really changed my life, losing that friend."

Shortly afterwards Ms O'Callaghan left her job in hospitality and began working in mental health.

Two years later, her dad took his own life.

"He was the best friend a girl could ever have. We could talk underwater," she said.

"We'd call each other and say 'hey, what are you doing? Want to go and get a bowl of laksa?'

"It took a long while for me to actually admit it ... but I felt like I failed him."

Ms O'Callaghan's renewed grief spurred her into action. Later that year, she set up the Hope Floats Foundation - a bereavement and education centre for loved ones who have experienced their own loss.

"My dad spent his whole life working to improve the lives of others. He showed up to make a difference," she said.

"There's a weird baton passing that I feel."

Ms Halloran says her brother would have been the first to sign up for the challenge.

"He'd have been the one doing all the cool tricks and crazy positions for push-ups - he'd be the inspiration to get people on board," she said.

"I think he'd be having a laugh at me struggling with the daily push-ups. But aside from that, I know he's cheering me on."

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Australian Associated Press