Britney Spears has ''self esteem problems''.

The 'Toxic' singer has been working with a fitness coach to arch her back as she believes her lack of confidence has caused her to ''slouch'' so she's doing her best to improve her posture.

She wrote on Instagram: ''Body language is everything!

''The way you speak to yourself and carry yourself can effect your mood .... I have self esteem problems so I slouch ... These poses help me everyday become stronger and it's quite fun doing them.

''I feel so different everytime I do it, cause I'm not used to the feeling of my back being out !!!!(sic)''

In the accompanying video - in which she wears a bright blue bikini - Britney balanced on her coach as he lay on the ground, holding up her upper body with his hands and supporting her butt with his feet, as she moved into different poses with her legs.

She explained: ''By hanging upside down it opens my back and it enables me to breathe better and to open up. And to feel better. So here I go.''

The 'Lucky' singer suffered a much-publicised breakdown in 2007 and it was recently claimed that she'd have died if it weren't for the efforts of her father, Jamie Spears, who took control of her affairs.

Dance studio boss Robert Baker recently said: ''I've known Britney since 1998. I saw her at the height of her fame and saw her struggling when things got tough.

''She was spiralling out of control. She was going through the worst time of her life and needed help.

''Her dad stepped in and gave her the help she needed. If he hadn't, things could have been very different. I don't think she would still be with us today.''

In recent years, Jamie has been accused of trying to exert too much influence over his daughter.

But Robert has rubbished those suggestions, insisting he did his best to protect the pop singer whilst she was placed under his guardianship after her breakdown.

Robert shared: ''All I saw was a loving, protective father who wanted to make sure she was safe.

''He's done an amazing job. Their relationship hasn't been the greatest, but he just wants what's best for her. I don't think he had any motives outside of taking care of her.''