Friends and colleagues of an intruder who died after an altercation with a homeowner in Sydney's south-west say his actions were out of character.

Key points: Bradley Soper was hospitalised for kidney failure before his death

Bradley Soper was hospitalised for kidney failure before his death He could not be revived after a physical struggle inside a Harrington Park home

He could not be revived after a physical struggle inside a Harrington Park home Homeowner Francois Schwartz was released by police without charge

Bradley Soper, 34, entered the house on Westwood Court at Harrington Park around 7:30am on Sunday.

Police said the homeowner discovered him in the lounge room and a physical struggle ensued.

Soper lost consciousness and died at the scene, despite neighbours' efforts to revive him.

The ABC has been told Soper had spent some time in hospital for kidney failure in the weeks leading up to his death.

It is believed the body builder and personal trainer's girlfriend had recently broken up with him, he was struggling for money and was also battling a cocaine addiction.

Brad Soper competed in strongman competitions. ( Facebook )

Fellow personal trainer Peter Tsikas said he was "pretty shocked" by news of Soper's death and did not think him capable of invading a home.

"No, he's a big teddy bear," he said.

"He's big and strong but he always loved people, so that's what doesn't seem right."

Mr Tsikas said his friend's death was at odds with the way he had lived life.

"He was a kind man, he always looked after everyone else first.

"It doesn't make sense and that's why we're trying to put the pieces together, because we don't know what's happening — it just doesn't seem right."

The scene at Harrington Park. ( ABC News )

The website for Soper's personal training business, School of Strong, said he had more than 12 years' experience as a strength and conditioning coach, personal trainer and athlete.

He entered strongman competitions, coming third in the Strongman Champions League world challenge in India last year, and was the winner of Asia's strongest man in 2017.

The owner of the Harrington Park home, Francois Schwartz, 44, was questioned extensively by police on Sunday and released without charge, pending further investigations.

His wife and young child were at home at the time of the incident.

NSW Police Chief Inspector Shane Woolbank said people were entitled to use reasonable force to protect themselves and their property.