The singer - who received online abuse over her appearance while competing in the talent competition - is said to have been inseparable from the gym over the Christmas period.
A source told The Sun: "Jesy's hired a trainer back home in Essex to make sure she's in top condition for the beginning of the year.
"The group will be busy soon so Christmas was a good time to get going. She's aiming to have a session three times a week."
The X Factor tour will start at Manchester's MEN Arena on February 25 before visiting Liverpool, Nottingham, London, Belfast, Aberdeen, Birmingham and Sheffield.
Following their win in December, Little Mix revealed that they are hoping for international success with their debut album.
> 'X Factor' Tulisa Contostavlos: 'Little Mix will be huge'
Watch the music video for Little Mix's 'Cannonball' below: