Dan Marshall was lethargic all the time and his diet was terrible.
"I used to think it was normal - I got used to feeling that way," Mr Marshall said.
"I'd come home from school, go to bed and sleep for 10 to 15 hours, get up and repeat.
"When I got to age 19, I hit a low point."
He was bedridden and forced to take time off sport and work.
"I had no energy and was paper thin," he said.
"I fell into depression and stopped going out and leaving the house as much."
After a few months of this, he was diagnosed with "low-grade coeliac disease - gluten intolerance".
This was back in 2003, before gluten-free diets became trendy. He cut out wheat and other grains.
"Almost immediately, I felt better. It was unbelievable. My energy and confidence started to come back," he said.
"I started getting back into the gym and feeling better. Through that, I became deeply curious about nutrition and exercise."
He looks back and thinks if that didn't happen, he "might not be where I am today".
It was this experience that prompted him to be part of a push-up challenge for charity this month.
People who attend his CoreFit Newcastle gym at Mayfield West have joined the challenge, which has involved doing a collective 3128 push-ups a day.
The aim was to raise awareness and funds for mental health, with proceeds going to the Men's Shed movement and Waves of Wellness.
The 3128 push-ups represent the number of people who took their own lives in 2017 in Australia.
Mr Marshall said push-ups were a great exercise because "they can be done by anybody".
"It releases those good chemicals like endorphins, dopamine and serotonin," he said.
Fitness fanatics often say squats are the best exercise, but Mr Marshall said push-ups were good, too.
"They use body weight and pretty much all the major muscles in your upper body. It also builds your core really well," he said.
Push-ups are invariably connected to punishment, the army, drill sergeants and the saying, "Get down and give me 20".
But Mr Marshall said they were better than burpees, which were "not anyone's funnest exercise".
"The push-up is a little bit more pleasant on the mind for most people," he said.
Asked how many push-ups he could do, he said: "My best is 55. After that my chest is about to explode".
"I've seen 100 straight done, which is unbelievable. That was an army guy. I'm sure he was well practiced."
Lifeline: 13 11 14
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