Millie Mackintosh's 'pull Up' Challenge

Millie Mackintosh can't do a pull up.

The fitness fanatic often posts pics and videos of her workouts to her 1.1. million Instagram followers and she is in incredible shape.

But despite the hours she spends in the gym there is still one exercise she can't do - the simple pull up.

She confessed: ''I can't do a pull up still. I was like, I'm going to do a pull up by Christmas. You need quite a lot of upper body strength to do it. I think weights are great to get that strong, athletic lean look. You can still be curvy but have like muscle definition in the right places.

''My workout shots get the most comments on Instagram, more than any of my other posts. And I love that most of the posts seem to be girls like tagging their friends, saying let's do this together.''

Speaking to News.com.au, Millie - who is married to rapper Professor Green - continued: ''I get really nice messages from people saying that I helped them get into fitness or made them feel good about themselves.''