"Even if you have to crawl towards your goals, keep going x it will be worth it," she posted along with a selfie peering into the camera in her workout gear.
"Try and give a little bit of effort each day … I know some days are frustrating as hell, you feel like giving up, you get annoyed at the lack of progress … but good things are coming your way," she wrote.
"What are your goals this year? I'll be honest with you guys – with my 'Year of Health' mission I'm trying to get to 75kg's and career wise am trying to get one of my movies into production before the end of the year! Both of these things are requiring a daily effort and there's constant set backs – but I'm working hard x," she told fans.
The post comes after the star, who turned 40 in March, vowed to cut out sugar and junk food at the beginning of the year, with fans noticing her weight loss in a beach snap shared in January.
"Okay so for me 2020 is going to be called 'The Year of Health' — so I put on the athleisure and went out for a walk, deliberately hydrating on the couch right now and trying to avoid the sugar and junk food which is going to be hard after the holidays I've just had but I'm going to do it! Who's with me in making some positive changes this year?," she wrote.
"I'm so proud of you!! You look fantastic already with your weight loss," one fan commented on the post.
"You look great, you look absolutely beautiful beforehand and still now. Such a role model," another agreed.
"You already look amazing! Killing it! Any positive changes are good changes," another fan said.
In the months since her pledge, the star's feed has been filled with snaps documenting her incredible fitness journey – including a raunchy at-home photo shoot earlier this month.
Rebel recently gave fans an insight into her fitness regimen by sharing videos of her gym workouts and revealing that she does cardio seven days a week.
In one clip shared on Instagram, Rebel can be seen doing circuit training including weight exercises, squats and lunges, before finishing off with ab exercises.
According to reports, the actress has been working with fitness guru Jono Castano Acero, and training with celebrity pal Hugh Sheridan.
"I encourage all my clients to do an extra bit of cardio during the day to keep moving," Rebel's trainer told HollywoodLife.
"A little tip is to get a watch or use your phone to count steps and aim for 10 thousand steps a day. If you're on 9000 steps at 10pm, you have to get it done."
She's also stopped counting her total calorie intake, and instead focuses on her fibre intake.
