Forget salads and crunches – a piece of string is the key to a flat stomach.

A leading physiotherapist says tying a thread around the middle can remind a person to pull in their stomach muscles, giving them washboard abs.

Sammy Margo, a chartered physiotherapist, says her simple string method can help people integrate abdominal exercise into their daily lives.

She said: 'Take a piece of string. Draw your abdominal muscles in all the way. 

'Release by 50 per cent and tie that piece of string at 50 per cent contraction.'

The pressure of the string will act as a reminder to tense the muscles.

She added: ‘Try bringing this into your day, when you’re walking, sitting, standing, working and at home.

‘Try holding this throughout the day for as much as you can.

‘This will give you a flatter stomach, work your core, improve your abdominal tone as well as improve your posture.’

Ms Margo told MailOnline the technique is a way to get people who might not carry out any exercise whatsoever to become active during the day.

She said: 'As physiotherapists, we are very concerned people are completely inactive.

'The prospect of going to the gym two or three times a week might be scary for some people so we need to find ways of integrating exercise into daily life.'

Even for those who go to the gym regularly, clenching the stomach muscles in the day will work them even harder, she added.

She said: 'If you switch on your abdominal muscles during the day, you're using them in a more functional, relevant way.

'In addition to the gym this is something you can do when you're not there - and we are all looking for convenient exercises.

'We're in the midst of a back pain and obesity epidemic, so anything to get people who may be physically inactive to engage their abdominals is going to help.'

Her advice comes as physiotherapists warn constant slouching leads to a hunched back, rounded shoulders and allow the stomach to fall forward, giving a bloated look.

Good posture, on the other hand, can make people look 10lb lighter, more confident and happier.

In fact, researchers from New Zealand found better posture leads to better mood.

They found that people who sat upright with their shoulders straight fared much better emotionally when carrying out a stressful public-speaking task than those who were hunched.

It is thought that posture affects mood because different muscle positions affect the functioning of our hormonal and nervous systems.

Another study, also from researchers in New Zealand, reiterated the importance of good posture.

Poor posture can make you depressed, angry and can even kill your libido, the study found.

People who slouch also use more negative words and become more self-conscious and self-absorbed.