Personal trainer's cruel joke at obese woman's expense backfires spectacularly.

A personal trainer has used his business page on Facebook to publicly shame a woman for her size.

Charles R Poliquin who refers to himself as the “strength sensei” shared an image of an anonymous woman with a caption that compared her body to that of a melting marshmellow.

The post was shared with all 217,000 users who have liked his page.

The caption accompanying the image read:

“Must be really hot in this shopping centre. She started to melt! Or many (sic) it is epigenetics, she is expressing the marshmallow gene because of her consumption of high fructose corn syrup.”

The post was soon deleted but not before it was picked up by another health and fitness page who took a screenshot of the post and shared it with their followers.

JPS Health and Fitness called the post “bullying” and said that such acts of public humiliation do little to help the problem of obesity.

“Bullying and making fun of those who are overweight and obese is not only morally incorrect, but is of no benefit to the problem and epidemic we face,” they said.

“For someone who claims to be a ‘leader’ in the fitness industry, it is disgusting to see him, let alone anyone, put down and make a mockery of someone who is out of shape.”

The shared image is currently gaining traction as users on Facebook comment on their disappointment with the trainer.

"Rethink your career. This level of unprofessionalism isn't just distasteful it should clue you in to who you authentically are. It ain't good," one user said.

Another user thanked the health and fitness page for reminding their community that bullying others over their physicality is a shallow judgment.

"Some people can't help their weight it's in the genes it's def wrong to mock or bully ANYONE for being different ty for posting this reminder," they said.

The post has even caused ire from members of the fitness community on Twitter who have tweeted their disappointment to Poliquin directly.

News.com.au reported that Poliquin had written an apology on the offending post before it was taken down, but he has said nothing since.

The apology reportedly said he was simply "passionate".

“I am passionate about reversing obesity. And like all passionate people, I go to extremes," he said.

“I hope that we all work together to conquer this problem and help people to live to their highest potential.”

Watch as Those Two Girls take you through the six types of people you'd find at the gym.