The idea of stepping into a gym used to make Jenniefer Gadsby, from Leeds, petrified.
Exercising when you are overweight can be daunting, and the fat-shaming attitudes of others do not help.
New research out this week shows people who feel discriminated against because of their weight are far less likely to exercise.
Jenniefer, aged 32, says she faced criticism about her weight.
It knocked her confidence so much that it put her off going to the gym.
"I would've rather done karaoke naked than set foot in a gym," she says.
"I was petrified. I was convinced that I would feel like the fat girl at the back of the class not knowing what I was doing and that I would get laughed out of there.
"What you need from people is encouragement, not them highlighting the problem. You know you have a weight issue. You don't need others pointing it out," she adds.
Jenniefer, who joined a Weight Watchers class, says she had always been large and by her early twenties she was unable to do up her size 24 trousers.
She wanted to make a change, but could not face exercising in public.
Instead, she began eating a healthier diet and took up walking, and the weight then started to fall off.
"One day I went past the gym and it was empty so I went in. I was still petrified, but I forced myself to go in," she explains.
She began working out with a personal trainer and has not looked back.
In her own words, she's now a "healthy size 10" and a gym convert.
She has become a qualified personal trainer and now helps other people get over their gym fears.
"You don't have to be thin to be fit. It's about encouraging people so they feel capable and, importantly, enjoy exercising, whatever their shape or size," she points out.
Dr Sarah Jackson from University College London carried out the newly published research into stigma and exercise.
She says the findings, based on interviews with more than 5,400 middle-aged men and women, shows what might work and what does not when it comes to encouraging healthy behaviours.
"Stigma may work for something like smoking cessation campaigns, where you highlight the harms of cigarettes," Dr Jackson says.
"But it's not the same for weight. Public health bodies are starting to understand that."
Sport England's National Lottery-funded This Girl Can campaign aims to celebrate women, of all shapes, sizes and levels of ability, becoming active.
The TV ad features real women and girls playing sport "in all their sweaty, jiggly glory".
A spokeswoman for the campaign said: "While lots of women worry that other people will judge them, research shows that once you begin to get active these fears lessen."
"Offering people a welcoming and supportive environment is key, and it's really important that the sports sector continues to find new ways of connecting with people who think that sport or physical activity isn't for them."
Jenniefer Gadsby says that sort of approach is great:
"A lot of gym adverts show people who are really athletic and that can be so off-putting," she says.
Gym group Fit4less recently came under criticism for some of its billboards.
One of its posters reads: "Tired of being... Fat & Ugly? Just be ugly at Fit4less from £14.99 per month".
Another, which shows an alien spaceship coming in to land, says: "They're coming... and when they arrive they'll take the FAT ones first!"
In a statement, the gym said: "Fit4less is a brand that doesn't take itself too seriously, the campaign is intended to be seen as light-hearted fun and we certainly don't mean to cause offence."
"Many health and fitness adverts feature the 'young and beautiful' in adverts. This campaign is designed to target people who do not respond to general health and fitness advertising and attract people who are not currently coming to gyms," the company explained.
It added that the general response to the campaign had been very positive.
"The vast majority of people are seeing it as a bit of light-hearted fun. This has always been our intention."