Michelle Bridges' mum was shocked when her daughter fell pregnant at 45.

Michelle Bridges’ inner mettle is evident. You can hear it in her voice when she yells at her trainees in the ‘Biggest Loser’. You can see it in the way she exercises… that determined look in her eyes as she performs lunge after lunge. And you can feel it when she talks about going back to work after giving birth to her son, Axel.

Now we know where she gets it from. Her mother.

“So hard to believe that a little girl from a very ordinary background… and nothing.. not one thing handed to her.”

Maureen Partridge – Bridges’ mother told Australian Story, which aired tonight, that their upbringing was lean.

After divorcing her husband when Michelle was around 4 years old, money became scarce and childcare difficult.

“I was cleaning houses to get some extra income but it was tricky when I had the girls sick and your boss would say you had to turn up regardless of what was going on at home,” Partridge said.

The celebrity trainer says watching her parents interact formed much of her no-nonsense attitude.

Partridge recalled an argument she had with her ex-husband.

"He upset me so much I started to cry. Michelle was in the bedroom and heard it. She got out of bed and snapped the phone off my hand and said 'Listen dad, piss off,'" she said.

Their meager resources meant that Michelle had to be innovative. She only had one school uniform. "It was a case of wash it each night, hang it on a little inside line, get up in the morning and iron it, so she had a clean uniform each day."

"I remember having my school bag completely and utterly ripped to shreds at the quadrangle, and everybody found it great sport," Bridges said.

Despite this, and constant bullying from other children who made fun of her single parent background, Michelle managed to make it as class captain at her new school.

Michelle found her solace in sport. "It was almost like I was free, like I was in my zone. I fell in love with the competition but I equally fell in love with the commitment and the discipline of the training aspect."

It was at school where she got her first sense of what she wanted to do with her life. "I could see there were kids on a Wednesday afternoon when we were playing sport that chose not to be a part of it."

"I went to my school mistress and said I can teach fitness to those kids. This was my first pitch into the business world. She gave me the green light."

Even though she had found her passion, Bridges' career took many dips and turns before landing in the fitness industry. Her first job at 18 was at a bank "I hated it."

She experimented with body-building and teaching Les Mills classes.

At 26 years old, she packed up all her possessions in a car and drove to Sydney. Her big vision was to get more Australians moving.

"I could see that my industry, the fitness industry, wasn't make a dent in the obesity epidemic that was coming."

Bridges' controversial views have landed her in hot water at times, but she's managed to take them in stride.

Her own mother was surprised when Bridges fell pregnant at 45 to her partner Steve 'Commando' Willis.

"It never entered my head that she would have a baby. It just didn't... she's a career girl" Partridge told Australian Story.

Michelle talks body changes and baby Axel with Mia Freedman for No Filter. Post continues after audio... 

"He is without a doubt, the most important thing" Bridges says of her son 4-month old son Axel.

What about the balance between work, life and family? A typical no-nonsense Bridges response:

"It'll work out. We will make it work."

Australian Story: Building Bridges can be watched on ABC iview.

Hear Michelle Bridges interview with No Filter...

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