Jessica Alba has started exercising again.

The 'Spy Kids 4' actress has begun a keep-fit regime in order to get her pre-pregnancy figure back, just two weeks after giving birth to second daughter Haven.

She tweeted: "I did my first day of wrkout since I had the baby, just cardio for 40 min. -it's a start. Anyone else starting a fitness regimen?(sic)

"my doc told me I could start after 2 wks. -im going light, stationary bike and elliptical"

Responding to tweets about returning to exercise from fans, she added: "start with walking and throw in 3 sets of lunges 20 per leg. U could do it while strolling ur baby. commit to 10 min a day for a wk then add another 10 until u get up 2 40 min a day. It's easier to ease into it.(sic)"

Jessica also revealed she doesn't stick to a healthy eating plan all of the time, allowing herself to indulge in her favourite calorific treats once a week.

She wrote: "i would keep ur diet as healthy as possible 6 days a wk and give urself 1 day to indulge.(sic)"

Before giving birth to Haven, Jessica - who also has three-year-old daughter Honor with husband Cash Warren - admitted she had been planning her workouts to get back in shape after giving birth, even though she hates exercising.

She said: "Working out every day for even just 45 minutes is good for my mental state.

"Getting dressed and actually doing it is the worst. It's hard to get motivated.

"In the gym, I have, like, five things to distract me: TV, iPod, magazines.

"Working partners are good, too, so you can chat and not just drown in your own misery. Sorry, does that sound bad? I just hate working out."