Just a day after Britney Spears showed off her bikini body on Twitter, her trainer, Tony Martinez, is revealing how she’s training to get in shape for her upcoming Las Vegas residency.

The “Toxic” singer posted pictures from set of her new music video for “Work Bitch,” and showed the results of an extreme fitness regimen.

"She's been a terror lately, working as hard as she can," Martinez told E! News. "She's using all sports right now to get ready for her 90 minute Las Vegas show."

Martinez says Spears’ 40-minute workouts are action packed, and she “loves to sweat.”

"It is intense, interval training to keep her heart rate up. In a show, she will be dancing and singing non-stop. In her training, she only has about 10 to 15 second rests between each set," he said. "She is doing Olympic-style training. This is hard-core stuff. Britney knew she needed to step up her game. She is just drilling it but she likes to! She loves to sweat and she still talks smack to me."

Martinez said he is confident in her that she is "mentally and physically 100 percent ready for Vegas.” He added, “She is working so hard. It is paying off. She is in a really good place and I'm so proud of her."

image: Wikimedia Commons