Baby one more time!
The pop star, 38, is on a mission to return to the taut form she'd lost after ending her Las Vegas residency -- and her routine involves lots of lifting heavy weights.
An insider told Radar, “Britney's body went to fat after she canceled her residency but she’s finally doing something about it. She’s spending three hours a day in the gym, minimum, lifting heavy weights and running marathons on the treadmill."
According to the source, the star is getting lots of support from her beau, 26.
"Sam’s the perfect trainer, always by her side to make sure she doesn’t lag behind.
"She’s drinking protein shakes and eating bowls of pasta for energy."
The insider added, "Her dream is to take it to the next level, and maybe even do this professionally.”
As Radar recently reported, Britney celebrated turning 38 last month in a bikini in Miami with Sam along for the romantic getaway.
Britney was spotted taking a plunge in the pool at her hotel and basking in the sun without her two sons, Sean, 14, and Jayden, 13.
“So much to be grateful for over these holidays,” Spears wrote on her Instagram days before her birthday, posting a picture of two candy canes in a milk jar.
As Radar has reported, Britney's vacation came after her courtroom drama with her dad, Jamie Spears.
After managing her life for more than a decade, he temporarily stepped down as her conservator amid health issues and abuse claims.
Her care manager, Jodi Montgomery, stepped in as the temporary conservator to replace her father.
Britney has clung to her main man Sam though it all.
Last fall, he won a Daytime Beauty Award in Hollywood for Outstanding Achievement in Fitness.
Sam was honored as “an actor and world-renowned personal trainer,” whose “fitness transformation has inspired the masses,” the organizers said.
"His positive influence has impacted thousands to achieve a healthier lifestyle. Amidst helping countless followers on their weight loss journey, he also finds time to give back to sports programs for kids throughout the year.”
But Britney's boytoy hunk is devoting most of his time now to getting her into rock-hard shape, the source told Radar.