Jennifer Lopez begins training for a triathlon six months after having twins

The actress appeared on a US television show in her workout gear as she told how she had been trying to get fit.

She said: 'The idea came up when I was about eight months' pregnant when I was beached like a whale .

Working out: Jennifer Lopez reveals her training regime as she prepares to take part in a charity triathlon in Malibu

'I was watching TV and I saw a triathlon, and I said, "I think I could do that. That would be great for me to do. Maybe I could do that this year." And of course everybody told me I was crazy.'

During her appearance on Good Morning America, Lopez admitted that she was nervous about completing the course. And she had some advice for triathlon hopefuls.

She said: 'You've got to start slow. You have to start little by little but just work up to it.'

The star will take part in a charity triathlon in Malibu, California, on September 14.

'Everyone said I was crazy': Lopez is completing the challenge to raise money for the Children's Hospital Los Angeles

Running women: Lopez says the thought of embarrassing her family by failing to complete the event is spurring her on

She is raising money for the Children's Hospital Los Angeles.

She joked: 'If I have to crawl across that finish line, I am going to.

'I keep telling myself that when I'm training, "This is for charity. Your kids are going to know about this. Don't embarrass the family! Get it done, Lopez!"

'I feel like my stamina, I can get it up there if I work really hard.

' the swimming is a killer, I'm not a natural.

'I'm always into challenging myself and seeing what I can do. It's really tiring but it's fun. It is hard, I'm not going to lie. But when I'm done I feel great, I have more energy.'

On your bike: Lopez admits that she is nervous about completing the course

Lopez gave birth to twins Max and Emme in February.

She said: 'The babies are great, they're amazing. I hated leaving them this morning. They're sleeping through the night. We're very lucky.'

The 39-year-old appeared alongside the editor of fitness magazine Self, Lucy Danzinger, who is helping the star to train for the event.

Lopez - who is married to Latin singer Marc Anthony - revealed earlier this month that she decided to take on the challenge in order to make her children proud of her.

Family affair: Jennifer and Marc with twins Max and Emme in June

'I thought, "What can I do to make my babies proud"' I think about what they'll think about the year they were born: who I was and what I did.

'It's important to me to set examples for them. I want to lead with my life. I want to say "You should do this because I've done it, and I know it makes you a better person and it makes you feel great and sleep better and be happier."'

Triathlons involve running, cycling and swimming.