Britney Spears has to be in peak physical condition when she performs in Las Vegas, and like scores of other celebrities from David Beckham and Scarlett Johansson to Hugh Jackman, she’s crazy about HIIT, the latest fitness trend.

Britney Spears has to be in peak physical condition when she performs in Las Vegas, and like scores of other celebrities from David Beckham and Scarlett Johansson to Hugh Jackman, she’s crazy about HIIT, the latest fitness trend.