She says: "I was a size zero. I wanted to actually have that curvy figure and that's why I got into training."
She thinks the trend started in America on social media.
"I think for girls, lifting weights feel good.
"Now they've got empowerment - they don't need a man for money.
"It feels good to walk into that gym, to walk into a weight room and curl more than a guy"
"Some people see it as a bit of self-obsession but I'd say it's the complete opposite.
"Every bodybuilder you meet, there's always a background story of why they do it."
Brittany was speaking to Adele Roberts from BBC Radio 1 as part of her documentary Why Women Want Muscles.
"It's torture, it's really hard"
"Going without food and sugar is probably the worst bit."
Brittany puts herself through a lot for her passion.
"I work a 50 hour week as a recruitment consultant. I get up at 4am to go to the gym and then go again after work."
And she has no time for people who say they've not got the time to train.
"I think there's enough hours in the day for anyone to achieve whatever they want - and not just in fitness.
"If you set a goal, start with 30 days then move onto 60 days - your body can change a lot. It can be done if you stick to the right diet and right training.
"Lifting weights is not going to make you look like a man"
"If you train smartly then you're not going to get a big chest.
"It's a lot harder for women to build muscle than men.
"People think they have to just do cardio to work out - but actually you burn more calories if you lift weights as well.