Steve 'Commando' Willis flexes his muscles as he warms up for charity fitness challenge with Miss Universe Australia Monica Radulovic

He is perhaps best known for his tough stance regarding personal fitness.

And Steve ‘Commando’ Willis didn’t hold back on showing off his athletic credentials on Sunday as he climbed 1,504 stairs in Sydney.

The 39-year-old Biggest Loser trainer showed off his muscular physique and as he competed in the Sydney Tower Stair Challenge, alongside Miss Universe Australia 2015, Monica Radulovic, to raise money for a charity that helps children with autism.

Scroll for video 

Stepping up for the cause: Steve ‘Commando’ Willis didn’t hold back on showing off his athletic credentials on Sunday as he climbed 1,504 stairs in Sydney

Stepping up for the cause: Steve ‘Commando’ Willis didn’t hold back on showing off his athletic credentials on Sunday as he climbed 1,504 stairs in Sydney

The father of three – and soon to be four - flexed his bulging muscles and gym honed body as he warmed up before the race.

Putting himself into the zone, the fitness trainer pulled his right leg behind his body to stretch his quads.

Steve, who is usually seen in wearing army pants, black singlet and dark sunglasses, changed up his usual attire as he opted instead for a black t-shirt that read 'Get Commando Fit.’

For a good cause: The 39-year-old Biggest Loser trainer showed off his incredibly muscular physique and as he competed in the Sydney Tower Stair Challenge to raise money for a charity that helps children with autism

For a good cause: The 39-year-old Biggest Loser trainer showed off his incredibly muscular physique and as he competed in the Sydney Tower Stair Challenge to raise money for a charity that helps children with autism

The top, upon which his running number was emblazoned, was teamed with a matching pair of dark shorts. 

The fitness guru, who has participated on the Biggest Loser show for six consecutive seasons, proved why he is nicknamed ‘The Commando’ as he appeared to complete the race with ease.

Showing off the tan he picked up during a recent holiday with partner Michelle Bridges, the star made sure to check his watch as he crossed the finish line.

The No Excuses author would have no doubt used his years of experience training others to help the 800 participants make it to the top of the 100 floor building, for the event which is estimated to have raised around $130,000 for the charity.

Fitness enthusiasts: Taking on the mighty challenge alongside Steve was pageant Queen Monica Radulovic (pictured fourth from left) - the pair completed the race alongside a number of other enthusiastic participants

Fitness enthusiasts: Taking on the mighty challenge alongside Steve was pageant Queen Monica Radulovic (pictured fourth from left) - the pair completed the race alongside a number of other enthusiastic participants

Also taking on the mighty challenge alongside Steve was pageant Queen Monica Radulovic.

The 24-year-old beauty, who is of Bosnian Serb ethnicity, showed off her trim physique in a pair of fitted black exercise tights which she paired with a khaki singlet and bright orange crop top which peered out slightly from beneath.

Wearing her honey brown locks slicked back into a high pony tail, the model flexed her long lean limbs as she also made sure to warm up extensively before the race kicked off.

Natural beauty: Monica, who is of Bosnian Serb ethnicity, flexed her long lean limbs as she also made sure to warm up extensively before the race kicked off

Natural beauty: Monica, who is of Bosnian Serb ethnicity, flexed her long lean limbs as she also made sure to warm up extensively before the race kicked off

Steve and Monica happily posed together for photographs before the race alongside a number of other enthusiastic participants.

Ahead of the race, the brunette stunner – who is an honours graduate in psychology - shared an Instagram image showing her with her partner, Sydney artist Alesandro Ljubicic. 

‘Instead of sleeping in this Sunday morning, @alesandroljubicic and I took out the #SydneyTowerStairChallenge,’ she penned to her almost 30,000 followers.

‘1504 steps, 100 floors and 309 metres of vertical height climbing the Sydney Tower Eye!!! All for a fantastic cause, raising money for the Giant Steps charity for Autism research – It was much harder then it looked but we did it,’ she added.

She made it! The 24-year-old showed off her trim physique in a pair of fitted black exercise tights which she paired with a khaki singlet and bright orange crop top

She made it! The 24-year-old showed off her trim physique in a pair of fitted black exercise tights which she paired with a khaki singlet and bright orange crop top

Meanwhile Steve has recently returned to Sydney after enjoying an extended ‘babymoon’ in Tahiti with Michelle, 44.

During their stay the pair populated their respective Instagram accounts with several snaps of their adventures.

Although technically a holiday, the athletic couple didn't miss out on any workouts - also sharing snaps from training sessions they had done on the tropical island.

The couple announced they were expecting their first child together last month.

'We're so happy to announce our special news. The well wishes and love we have received already are overwhelming and beautiful. Thank you so much,' Michelle posted on social media at the time.

Babymoon! Meanwhile Steve has recently returned to Sydney after enjoying an extended holiday in Tahiti with his partner Michelle Bridges, 44

Babymoon! Meanwhile Steve has recently returned to Sydney after enjoying an extended holiday in Tahiti with his partner Michelle Bridges, 44

Keeping fit: During their stay the pair populated their respective Instagram accounts with several snaps of their adventures

Keeping fit: During their stay the pair populated their respective Instagram accounts with several snaps of their adventures

No rest for the wicked: Although technically a holiday, the athletic couple didn't miss out on any workouts - also sharing snaps from training sessions they had done on the tropical island

No rest for the wicked: Although technically a holiday, the athletic couple didn't miss out on any workouts - also sharing snaps from training sessions they had done on the tropical island

Parents-to-be: The happy couple announced they were expecting their first child together last month

Parents-to-be: The happy couple announced they were expecting their first child together last month

 

The comments below have not been moderated.

The views expressed in the contents above are those of our users and do not necessarily reflect the views of MailOnline.

We are no longer accepting comments on this article.

Who is this week's top commenter? Find out now